Neil's Corner

by Neil Cairns

The following are a series of articles written by Neil Cairns, formerly MG Car Club Safety Fast scribe. Some of these articles will be of a general MG nature, others specific to the Y Type and / or XPAG engine.

Neil's notes

reproduced from Safety Fast - the journal of the MG Car Club

Universal Joints

Things creep up on you, often unnoticed. They accumulate. This was the case with noise and vibration on my YB. Eleven years ago (I keep the old receipts) I fitted a stainless-steel exhaust system and new universal joints (UJ) to the prop-shaft. That was about 26,000 miles ago. Recently I had noticed that reversing the direction of the car produced a loud clang from somewhere underneath. I recognised this noise as that of a worn UJ and the prop-shaft acting as a 'bell'. So I jacked up and supported the car so as to get a good view of the shaft. Grasping the shaft itself by the doff unit, and the flange of the doff in the other hand, I twisted the shaft across the UJ in opposite directions. I could feel movement; this was wear in the needle rollers inside the cups of the UJ. I had used replacement UJs of the type that are sealed for life; i.e., no grease nipple to re-charge the unit each servicing. I then checked the gearbox end in a similar fashion, but the access was not so easy. it too had slight wear. This wear led to the rear view mirror vibrating at 50mph to a blur. It also was producing the noise in the cabin making 50mph cruising uncomfortable. As this had slowly been happening over 11 years one does not notice it, one just drives a bit slower. Checking the front UJ by the gearbox also led to me getting a very close view of the silencer. it had a big crack right round theentry pipe, which was obviously blowing.

So, with NTG sending me a new silencer within 24 hours, and me having purchased two new UJs from the Octagon CC some years ago in anticipation of this day, I removed the shaft, and the exhaust from the silencer back. Using two socket spanners I pressed out the UJ cups in the time-honoured way in my big bench vice and fitted the new ones. Oh, does that not sound so easy? it did take over two hours to do and great care has to be taken to not let any needle rollers drop inside the cups as you fit them. I primed them with molygrease. Both new UJs had holes for grease nipples as well so I can now service them along with the many other bits that need regular greasing. Refitting the stainless-steel exhaust was easy, and I had been amazed at just how easy it had all come to bits after 11 years under there. No rust to seize it all up, only the rear exhaust clamp had corroded, but i fitted new ones all round anyway.

Refitting the prop shaft took no time, and back on the road apart from a little exhaust blow from one clamp (cured with silicon sealant) the car is much, much quieter. The rear view mirror no longer vibrates and there is no loud clang on reversing.

Gearbox and Rear Axle Ratios

Gearbox Specifications.

Remember, the 'ratio' given is the gearbox, but it is then multiplied by the rear axle ratio, so that is included as well. Two identical gearboxes fitted with different ratio rear axles, will appear different on paper as the overall ratio's will not be the same. ( i.e. top gear ratio will be 1 to 1 in the gearbox as it drives straight through, but the overall ratio will be 1 multiplied by the rear axle ratio, 1 x 5.125 = 5.125. Second might be 2.25 x 5.125= 11.547.) There are two different rear axles, one by Morris and the other by Nuffield. They may all look the same but their wheel-tracks differ and the later Nuffield one is very much stronger.

Oil suitable for the post was cars is SAE 90 EP, pre-war SAE 140.

The following tables have also been produced by Tony Slattery and appear in our Hints and Tips page.

Understanding (decoding) UK Licence Plates

SINGLE LETTER Registrations, by area.

First issued from 1903, but some were reused as offices ran out of numbers in the late 1950's & early 60's i.e. 'A 166'.

DOUBLE LETTER Registration by area.

Note that some letters were re-allocated in both 1974 and 1981, as busy Registration Offices ran out of the original letters. issuing in the old area then ceased as the new Office began using them, and in some cases letters have been in three different areas countrywide!  This lack of space is shown as '74 or '81.  Most were issued to their areas originally in 1903, under the "Motor Car Act 1903" i.e. 'A 166', 'AB 166', and later 'BAB166', and after 1963  'B166 BAB.

Suffix marks introduced in 1963, but not all authorities used them until late in 1964. Starting dates.

NOTE: An excellent book, now out of print, but often available from a library, is by Phillip Riden, Trace the History of Your Car, 1991.ISBN 1 873361 05 X. This goes into which authorities have kept records (many of which have not) with addresses you can write to in order to obtain a copy of your cars initial registration.

Today, with the selling of registration plates by Swansea, tracing is not so easy any more. DVLA can help with post 1974 cars, and addresses of your Local Vehicle Licensing Office can be found at the main Post Office in your town.

This document relates to registration / license plates issued in the United Kingdom only.

Buying and Running an old MG Y

The Running Gear.

So you have decided to buy a MG 'Y' series. You have read up on all the road tests available, and the excellent books 'Let there be Ys' by David Lawrence and 'MG Y-Types  Saloons and Tourers' John Lawson (both available from the MG Car Club Y Type Register website www.mgytypes.org). You sent off or downloaded the reprints of  the Practical Classics back-copy on Buying A 'Y', of November 1993, the MG Enthusiast Magazine 'Y' Type article of Feb/March 1985 and Popular Classics Magazine 'The Y Type of November 1993, (now available from Practical Classics) and you have read the reprint of the article from Practical Classics December 1984 reprinted in Brookland's book MG Y Types and Magnettes ZA/ZB (also available from the MG Car Club Y Type Register website www.mgytypes.org). You have been to a few MG shows, and have spoken to 'Y' owners. The car is what you want, and you have a good idea of its abilities, running costs, spares availability, insurance, etc. Now it is time to look at the cars for sale to find your ideal version. Always, always do your homework before you buy a car, impulse buying will only lead to tears and an overdraft.

In this article we are going to look at the running gear, this includes the engine, gearbox, rear axle, steering and suspension. The car has many grease nipples that will require attention every 1,000 miles, and oil changes at every 3,000 miles. Servicing an older car is quite an expense if you cannot do it yourself. Fail to service it properly and things will seize up and break. Service it properly and most of it will last for ages and ages, well beyond that of the equivalent sealed-for-life modern car part.

The MG 'One and a Quarter Litre' sports saloon is 'of its age". That simply means the car is not a 1990's sports hatch, and cannot hope to keep up with modern motorway traffic. Under its bonnet is an engine the origins of which date its design back to the 1920's, while at the same time having some very modern engineering inside it. it is an overhead-valve (ohv) unit of 1,250cc giving out 46 brake-horse-power. That is only 1,250cc pulling a car weighing over a tonne, so today the performance may seem very pedestrian. in 1937, when the car was conceived (to be ready for the 1940 motor show), its 70mph max speed was very good, its specification excellent, and its road holding superb. This was in comparison with other four door family saloons, of the late 1930's. Many had elderly, long stroke, asthmatic side valve engines of very low power. The little MG sports saloon was the VW Golf GTi of its day, (or even a BMW 2002 of the 60's for you older enthusiasts). Note this was the late 1930's, so to drive a YA, YT, or YB today requires very careful road Reading, as most modern motorists will not understand your cars lower performance.

If you are going to look at a restoration job, the engine is going to need a full rebuild, as is the gearbox, brakes, suspension, steering and rear axle. For the engine alone, you should budget for £1,500 plus. Gearboxes often only require new bearings and oil seals, rear axles the same, though note that the one fitted to the YB is the later hypoid type and longer available. (The YA  has the older spiral-bevel axle, whereas the YB has the later Nuffield axle.) As you will have read all about the cars, you will also know the braking system's differ, twin leading shoe on the YB, and single leading shoe on the YA/YT. While the 'Y' series look as if they come from the 1930's with their upright styling, the independent front suspension (designed by a young Alec Issigonis), rack and pinion steering, ohv engine, three synchromesh gearbox and hydraulic brakes set the standard for cars of the late 1950's. The steering and suspension were used on the TD, TV, MGA, MGB undergoing only slight modifications before finishing up on the MG RV8 1993!

If the car you are going to see is a runner, and advertised with an MOT, tax, and driveable, then you can do quite a bit to check out the running gear.

• When you arrive have a long chat with its owner. An enthusiast will tell you a great deal about the car, any work done, and possibly anything that will need work. Check the engine is not hot, as you will want to see how the car starts from cold.
• Walk about the car, does it sit level, what are the door gaps like, tyre condition, how clean is the engine, battery condition, (take its cover off), what is the wiring like? You are getting a general feel for the car, its condition, how it has been kept and serviced.
• Look underneath at the kingpins (front suspension main vertical piece about which the wheel turns), is there clean grease coming out of them? Or are they dry and rusty looking?
• Take out the engine dip stick, look at the oil, is it clean or thick black muck?
• Take off the engine oil filler cap, is it clean inside or is there lots of white 'mayonnaise'? This white foamy looking stuff tells of a cold running engine, possibly with an internal water leak. Grey oil is an indication of oil mixed with water.
• Look underneath at the engine sump. if it is all dry and clean that is very suspect, as these old engines all weep at the timing cover seal, and the rear crankshaft seal after a few miles. The front seal is a bit of asbestos rope, the rear seal a reverse-scroll type (unless a new seal has been expertly fitted — ask to see the invoices for this work and the parts). These engines were being built a long time before neoprene spring loaded lip-seals.
• Look where the car is usually parked, that will tell you how much the engine/gearbox/rear axle leaks. The gearbox should not leak, but the speedometer drive may seep a little. The rear axle again should not leak. These two units have leather lip-seals.
• Check the steering rack boots for splits and leaks whilst you are underneath, (MGA ones fit). So far, you are just looking at things, we have not actually tried the engine yet.

So, now get into the drivers seat, pull out the choke if it's a cold day, turn on the ignition, and pull (or push on some very early side battery box YAs) the starter button. All 'Y's fire up instantly so long as you let the fuel pump tick away till the carburettor float chamber is full. When you started the engine, a glance in the rear view mirror would have shown you a puff of blue smoke. This will be oil that drained down the inlet valve guides.

• These engines DO USE OIL, it is quite normal, it is how much that is important. Blue smoke on starting up is nothing to worry about.
• The engine should idle over a little fast with the choke out, but look at the ammeter, it should be charging a little after the use of the starter motor.
• Glance at the oil pressure gauge which should be creeping up to about 50psi. Once the engine is hot, the oil pressure will be between 15 to 60 psi depending upon the condition of the engine, at idle rpm. But at 30mph it should be firm on 50psi when the engine is hot. People worry a lot over oil pressure, and it is one of the easiest 'pressures' to boost by adding washers to the pressure relief valve. As long as it is over 40psi at 30mph, and at least 10psi at idle, there will not be a great deal wrong.
• It is the sounds the engine makes that is important. it will 'tick' a little from under the rocker cover, as these engines are very 'tappety'. Now leave the engine running whilst you listen to it.
• Wait until the radiator cap is hot, (there is no water temperature gauge on these cars, and the system is not pressurized.) This will take a good ten minutes.

Blue smoke all the time that the engine is running though, is a hint of serious wear. To check this out we need to go for a drive. But before this, open the bonnet and look under the water pump at the front of the engine. Any water dripping from here shows the water pump is worn out.

• Look down at the engine breather, the pipe that runs down behind the distributor. There should not be any smoke coming out of this, though a small amount of oil vapour may stain the chassis. Remember, these old engines do not have enclosed breather systems as on modern cars. Many of them leave a little 'fingerprint' of their oil drips when parked, not something people with posh driveways relish. Only a new XPAG engine does not leak, or else one with an empty sump! Leakage includes that oil mist that escapes via the breathers. A very oily rocker cover may indicate the engine has worn pistons and rings, as the oil is blown out of the oil filler cap and from the vent pipe to the air silencer/filter mounted above the engine.
• Take a look at all the core plugs you can see. There are five of these on the inlet side of the engine and none of them should be weeping. Any with signs of rust may be about to burst, loosing all the coolant. Replacement is more fiddly than expensive though.
• Listen to the front of the engine. A rattle at the front of the engine may be a worn timing chain. This will require the sump to be removed to change it, not an easy task.

Now, having done all of the above, take the car for a run.

• The clutch should be firm and easy to operate. Glance down at the pedals as you push in the clutch, the brake pedal should NOT move. They run on the same shaft and if not lubricated can become very stiff and interact. This is an MoT failure point.
• The first gear will need firm engagement as it uses direct cogs, (as does reverse) and all the gears will seem to have low ratios.

• Unless you are an expert at double-de-clutching never engage first with the car moving.Drive off and change gear as required. Second, third and top will be easy as these have synchromesh. Now go back down the box, but NOT into first. Do this a few times to check the synchromesh is good. if the gears crunch a little, try double-de-clutching as this may improve the change. The gearbox should not be noisy, but sometimes the rear axle can whine. This is more noticeable as you get nearer 60mph. The gear lever may 'zzizzz' at speed, this can be bearing wear inside the box, or just the rear axle sending its whine up the propeller shaft.  There should not be any loud clonks from the transmission. If there are the propeller shaft universal joints may be worn, or the flanges may not be tightly done up to the gear box / rear axle.

• The steering should be very good and positive, the rack and pinion and independent front suspension make the car feel very modern.
• If cross ply tyres are fitted, they will scrub on fast corners, if radial ply tyres are fitted the car will run quieter but the steering will be much heavier. That is why the steering wheel is so big, - to give you the leverage.

The brakes on the YA are good, but those on the YB far better. Both cars need a very firm foot on the brake pedal, as there is no servo assistance. Basically the harder you can push, the better they are. The pedal should be firm and only go down half way. Again it should not move the clutch pedal, or hit it by sideways movement.

The car is pleasant to drive, and in its element between 20 and 55 mph. it will love secondary roads and winding lanes, but fast trunk roads will be hard work, and motorways far too fast. You must learn to use the rear view mirror often, and give plenty of time to pull out of T-junctions.

Upon returning from the run, leave the engine idling over for about ten minutes, and then blip the throttle.

• Only a small amount of blue smoke should come out of the exhaust. if there is a lot, the engine may need a rebore, and probably new valve guides. This is expensive. Ask the vendor is the engine is converted for lead-free petrol. if not, then the valve guides fault will be cured once new valves and guides are fitted. Worn pistons are another story, and will mean an expensive engine rebuild.
• On the drive there should not have been any rattling from the engine, and the oil pressure should have remained about 50psi when on the move. Now, after the run, with the hot engine idling, look at the oil pressure gauge. if there is virtually no pressure, this will confirm the engine is worn out if there is blue smoke from the exhaust pipe.
• Check the carburettor now, there should not be any fuel leaks.
• Look under the car to see if any oil has magically re-appeared where all was dry before the run. People have been known to clean the sump off with carburettor cleaner, this makes it look oil free. Small drips are not too serious and can be lived with.
• Undo the radiator cap with a cloth, (it is not pressurised) and see where the water level is. it should be at the bottom of the filler neck., if it is out of sight, where has it gone? Look underneath for drips. inspect the radiator matrix carefully, as this is expensive to rebuild. Do this with the engine stopped, or the cooling fan will take your finger off.

What is your impression? if you like the car now is the time to give other items a firm check over.

• Jack up each wheel in turn and check for worn wheel bearings and tyre condition.
• Spin the steering from lock to lock, checking for play in the king pins with a tyre lever under the wheel, lifting the lever gently from below as the MoT examiner does to see if there is play in the kingpin.
• Look at brake hose condition, there should be no cracks.
• Check brake pipes for corrosion.
• Look hard at suspension fixings and rear spring hangers for rust.
• From underneath, grasp the very rear end of the gearbox and shove it up towards the floor hard. it should not move, unless the rear eye-bolt is broken. This eye-bolt holds the gearbox down onto the cross member, and sometimes the casting cracks if the car has been 'jumped' over bridges, etc. The action of the car landing forces the prop-shaft forward, and this can hit the gearbox breaking this mounting.
• Check the universal joints on the propeller shaft, do they look dry and rusty? Grasp the shaft each side of a joint and try twisting in opposite directions. Any play is bad news.
• On the YA/YT look at the chassis to rear axle Panhard rod, are the end fixings in good condition.
• On the YB look hard at the front anti-roll-bar. This differs from the MGA/MGB fixing, and can crack at the lower spring pan mounting points

The front damper is part of the upper suspension arm. if the trunion does not get greased regularly, the bolt seizes in the trunion, and twists in the damper arms. Eventually it will break, and you crash! The guide is fine rust dust around the bolt ends, and an awful squeak when depressing the front wings.

Grasp the car at each bumper corner and bounce it up and down to see if the damper on that corner works. Any leaks from the damper mean fitting a reconditioned unit, more expense, and an MOT failure if you do not.

The Jackall system may not work, though many do but on the front end only. You can try it out, but the rear axle hose has often burst, and the rear jacks have seized up. Use ordinary motorcycle fork oil in the reservoir. Never trust the Jackall system to go under the car, without axle stands. Many MOT examiners mistake this tank for the brake master cylinder reservoir. The master cylinder is under a little steel cap under the floor of driver's seat. The floors are wooden,  so be very suspicious of cars fitted with seat belts, as they may not have sufficient anchoring strength.  Remember, if you lower the Jackall rams, you must ensure that the rams are fully retracted before moving off in the car, otherwise substantial damage will be caused to the rams.

Looking under the car again, at the back of the brake backplates, look for damp areas where brake fluid has seeped out. if there is any doubt over brake cylinder leaking, take off that wheel and brake drum to check. YA and YT will need the cylinders re-lining, though the YB uses the later TD items. Maybe just a seal kit is needed.

The XPAG engine used in the 'Y' series is based on a design first fitted to the Morris Ten/4 of 1938. This engine was also fitted to the MG TA. it proved to not be very tuneable, so it was updated and had a certain amount of redesign to become the 'Short Stroke Morris Ten 'M' engine of 1,140cc in 1939. This was opened out to 1,250cc and fitted to the MG TB as the XPAG. The TC, TD and TV also used the 1,250cc engine up to 1955, as did the Wolseley 4/44 from 1952 to 1956. it is a tough unit, but suffers the common faults of early overhead valve types. That is a high wear rate of the camshaft, followers, rocker arms, rocker shaft and valve guides. The timing chain also rattles if the oil pressure gets low, as it has an oil-pressurised tensioner. The long stroke also means rpm is limited, so long runs at high speeds leads to bore and piston ring wear. it has shell bearings fitted on the crankshaft, so these can be renewed. The oil pump is an excellent one, and will be more than capable of feeding any quantity required. it has a pressure relief valve that operates all the time once 50psi is reached. This is why putting a couple of washers behind the valves spring will 'artificially' boost the oil pressure. The Morris Ten/4 series 3 and Wolseley Ten/40 used the 1,140cc engine, up to 1947. This can be bored out to 1,250cc if required. For more information is available on this engine as a free download, click here for a copy.

Other points to consider maybe:

• Where will you get the spares you need?
• How much will it cost to insure, and do you need agreed-value insurance?
• Where will you store the car?
• And more to the point what space will you need if you are to strip and rebuild it?

Owning and driving a classic car of the 'Y's vintage means a lot of Tender Loving Care is needed, constant servicing and watching for signs of faults. The MG Car Club offers lots of technical advice to Y owners via its website at www.mgytypes.org, and the 'Y' Register has people with many years of experience to help you. You only have to ask!

Does your MG smoke?

Does your MG smoke?  Has it developed a bad habit that has caused you grief on the annual Mot check? Does it drive perfectly alright, use a little oil, but failed its Mot on excessive exhaust smoke? Then you probably run a MG fitted with a well used 'A' series, a worn 'B' series, or a tired 'O' series. All these engines are related to one another, being a development of a pre-WW2 Chevrolet six cylinder lorry engine. Vauxhall used the same lorry engine, as they were owned by General Motors, who own Chevrolet. Austin copied the engine in a mirror image, (by reversing the camshaft position) and put it into their commercial vehicles, and limousines. Austin then developed a large four cylinder, and smaller four cylinder version's of the same engine. These went into the 1947 Austin A40, and the larger Austin 16, (and the Atlantic, taxi, Austin Healey, and vans). in 1952 the A40's engine was redesigned into the 'B' series, and a smaller 'A' series in 1950. This is a very great simplification of the story, but it continued into the 1980's with the now larger 'B' series becoming a single OHC unit, called the 'O' series of the Montego and Maestro; and the 'A' series becoming the 'A' plus in the Metro. (The 'O' was actually about in the early 1970's in an MGB, and the 1275cc 'A' in the Mini Cooper 'S'.)

So, the engine in your MG Metro, Montego, and Maestro is a very old design. it has been updated and modified over the years, but it is still old technology. All these Austin, BMC, BLMC, BL, Austin/Rover engines suffer the same old age problems. They all have pretty long strokes and heavy reciprocating masses inside.  The 'A' continues as an OHV unit, the 'O' had a better OHC cylinder-head head; both used what is basically a 1950's bottom end.  Now, back in the 1950's BMC engines were well known for lasting 80,000 miles, or even 100,000 if well locked after. This was when the side valve Ford engines were completely worn out by 35,000 miles, and their OHV engines at 60,000 miles. Ford has improved markedly since then, but the basic BMC engine has not. A 1275cc MG Metro will show signs of its high mileage at the 80,000 mile point, and many will be burning oil. The 'B' engine fare a bit better to the 100,000 mile point, but then it is world famous for running well even though it is a total wreck inside. The 'O' series inherited this 'longer' life, now though it is only two thirds worn in a modern car. Today Vauxhall 'Opel' based OHC engines run till 180,000 with just the camshaft needing a swap at about half that distance, Fords are similar.

Back to your MG. The much larger tolerances of the engines in the Metro, Montego, and Maestro, give much more movement to the parts inside. For instance, as the piston rises and falls, it moves sideways a little, (only a few thou', but enough). This leads eventually to the groves the piston rings run in, wearing. The piston will slide sideways on the piston ring as it changes direction. After a few million reversals of its passage in the bore, the bore itself, at the upper end, will wear. So you now have a piston with piston rings that are a loose fit. As the piston descends the bore, the rings are forced in a little, back into their grooves. As they descend they collect oil, which is forced behind the ring, into the groove past the lower face. This lower face has a gap caused by the wear mentioned above. At the bottom of the bore, the piston changed direction, and the ring is quickly collected by the lower part of its groove. The oil caught behind it is forced above the ring. The oil is passed up to the next ring on the next descent, and thence to the next ring. it may only be a tiny amount per piston stroke, but it makes a pretty efficient pumping system. At high speeds on long motorway journeys, your engine can drink the sump dry. The oil control ring will be worn, and its drain holes clogged with carbon, as well as the main and big ends being a little worn, so copious amount of oil get thrown up the bore that it cannot deal with.

So the first thing that may be wrong with your 'smokey' MG, is ring pumping. The cure is a re-bore and new pistons. A test is to leave the engine idling over for a long time, then blip the throttle. Blue smoke is a bad sign, BUT this may also be inlet valve guide wear, see following.

On the OHV MGs, but not so badly on the OHC versions, is the wear of the inlet valve stem, that in its guide, and the hardening of the stem seal with heat and age. Whilst the rings are lifting oil up the bores, the inlet valve guides are sucking it into the inlet manifold. The test for this common old-age fault is easy. Get the engine nice and warm, and then take a drive down a long hill that requires you to run most of its with your foot off the throttle, but at a good speed. This will create a very low pressure in the inlet manifold, and if the seals/guides/and stems are worn, oil will be sucked into the manifold. At the bottom of the hill give the car a good boot-full of throttle, whilst watching in your rear view mirror. if there is lots of blue smoke, get that cylinder-head seen to ASAP. The cure is new guides, valves, and seals. if yours are un-worn, then just a new set of seals will cure the fault. DO NOT fit seals the exhaust valve stems, or they will seize up.

There is a third cause of smoky exhausts. On cars with enclosed breather systems, when the engine wears a little, there will be piston-blow-by. This is the combustion gasses escaping past the rings into the crankcase. This leads to the engines venting system getting worked rather hard, and oil mist to be sucked into the inlet manifold. There should be an oil-trap to stop this, but if the engine is virtually blowing into the vent system, it will soon get overwhelmed. The reverse is also true, where the vent system has never been serviced and pipes are clogged up with carbon. This lets the crankcase pressure rise and helps shove oil up past the rings on the 'inlet' stroke. This also pressurises the crankcase and blows oil out of the various seals. Oil consumption by the vent system is easy to prove, disconnect the system and see if the smoke stops. This is not really a short cut to passing the Mot though, as with a disconnected system the engine will run richer, ( if you seal the inlet to the manifold,) and at speed you will have even higher crankcase compression. The cure is usually a re-bore.

Attempts at sticking nicotine patches on the wings have proved to fail. if you have a smoking MG, find the cause and fix it.

Ring pumping

When quite a number of issues of this booklet had been sold,I began to get some feed-back. One question that cropped up more than others, was the technical term 'ring-pumping' on page 17, under Oil Consumption. Now, grizzly old, black-finger-nailed mechanics like myself often fail to explain things fully. it is a common fault amongst all followings, and it is possible that a bank manager, quantity surveyor, criminal solicitor, head teacher, and many other non-engineering careers, have never heard of the term, before. Their reaction was probably the same as mine when my bank manager suggested to me I might think about a 'free-standing AVC' some years ago, (it is an extra pension, uses up your 'percentage' permitted by law, to the full; or did until the stock market fell to bits).

A internal-combustion-engine turns heat energy into a rotary motion. it does this by burning its fuel inside a cylinder, causing a pretty fast expansion of the gasses inside. These gasses in our MGs are air and petrol vapour and are set on fire by a spark plug. (Note it is not an explosion, but controlled burning.) in our MGs the engine works on the 'Otto Cycle', as he first designed it back in the 19^th century. it is called a four-stroke cycle, or simply SUCK, SQUEEZE, BANG, BLOW, (inlet, compression, ignition, exhaust). The item that does all this work is the piston, in the XPAG this is an aluminium alloy, oval-ground to take up expansion when heated equally, (called controlled-expansion) and is fitted with piston rings to seal the cylinder bore. The piston goes up and down, the crankshaft round and round, and this is termed a reciprocating motion, (like a knee and a foot on a bicycle). Like your knee on you cycle, at the top, and the bottom of each 'motion' up or down, it comes to a stop. in the middle of this 'motion' (or thereabouts) your knee is moving pretty fast.

The piston is the same, it stops at the top of the bore, and the bottom, (called Top-Dead-Centre, and Bottom-Dead-Centre, TDC and BDC.) The piston then has to accelerate down (or up) the bore to the mid-point, then decelerate as it approached the bottom, (or top) Each time the piston changes direction, it thrusts itself against one or other side of the bore, depending upon its direction. The worst wear occurs on the thrust-face on the down stroke during combustion. The 'power-stroke' thrust causes more wear. Your XPAG engine has four pistons, set in pairs, that is two are going up as the other two are going down, (i.e. 1 & 4 up, 2 & 3 down). Each piston has four piston-rings. The top two are termed compression-rings. They seal the piston in the bore, and attempt to stop the mixture escaping down into the sump. There has to be a gap in them, to permit expansion, and accommodate wear in the bore. The other two rings, one just above the gudgeon pin, the other in the piston's skirt, are oil-control rings. Very early XPAGs only had one oil-control ring. if you still only have one oil-ring, you probably have after-market pistons and will soon use oil. (Ordinary Morris and Wolseley saloons that used the XPJM and XPJW, the 1140cc version of the 1250cc XPAG, only have one oil ring, but they are a much smaller diameter so will not fit you MGs engine). MG 'X' series engines are fitted with two oil-control rings, as they are designed to operate at higher rpm figures than the cooking Morris & Wolseley versions.

The oil-control rings try to stop too much oil getting up into the combustion chamber. So the compression rings try to stop gasses getting downwards; and the oil rings try to stop oil getting upwards. Some oil MUST get upwards, or the engine would seize up, or at best the cylinder bores would wear away at a terrible rate. Some gas will escape past the rings, and cause crankcase compression, in older engines. This then causes oil leaks past seals and gaskets. Like the piston, the rings have to change direction every time they get to TDC and BDC. They also have to have room to move about in their groove in the piston, and the piston has to have room to expand and contract, and let lubrication get to the cylinder bore walls. Also, the very top of the cylinder where the top compression ring runs to, has the second highest wear rate in the engine, (first is the camshaft lobes). The XPAG has a hot water jacket to the bottom of the area the compression rings run to, in their bores. This is good design, and keeps wear low.

Now that you hopefully understand all this, you need to speed it all up in your minds eye. imagine the pistons going up and down as you drive your MG at 50 mph. The engine will be rotating at about 3,400 rpm. As a petrol engine is really quite a feeble machine, it can only get its power by rotating very fast. Brake Horse Power, (bhp) figures rise in line with rpm, so 3,400 rpm is not high today, but it was pretty fast in the days of your car. The XPAG was a sports engine and one of the most powerful of its size for its day, for a production 1250cc engine. Now, if the crankshaft is spinning 3,400 times every minute, those pistons are going up 3,400 times, and down 3,400 times. Now really blow your mind and work out just how many times they did this on your last 20 mile run out. Now try working out how many times they alternated their direction in those bores, since the engine was assembled, or re-bored! As the top of the bore wears a little, not only do the rings go up and down with the piston, they begin to move in and out of their grooves a little to take up the wear. The 'movement' is because the top wears more than the bottom. This movement in the grooves will begin to wear away the edges and the piston ring sides. The ring becomes sloppy, and oil can get around it.

As the XPAG is a relatively long-stroke engine, (90mm, but the TA was 105mm) and long stroke engines are usually good at giving high-torque, (torque- a turning power) and most often engines of the XPAG's type give their highest torque figures at about their mid-range rpm (YA gives 58lb/ft at 2,400rpm, the TD gives 63; the TV 65lf/ft at 3000rpm). This indicates that the car will be most happy between 40-55 mph in top gear. But the longer the stroke, the faster that piston has got to travel to get from the top to the bottom every time. The pistons speed can get very, very high, and at 2,500 rpm this is 65 ft per second. This would be true of any engine with a 90mm bore, such as the MGA - MGB's BMC 'B' series engine.

So at about 45 miles per hour in top gear, you engine is at its most efficient, and those pistons and rings are belting up and down each of the four cylinder bores, and starting and stopping at every TDC and BTC. No wonder the thing vibrates a bit! As they stop and start the piston has to collect the rings, who might be a few thousandths of an inch, (termed 'thou') behind each piston. As the bores wears, so to do the grooves the rings live in. And as the engine ages and the ring's grooves wear, the rings themselves wear, and the cylinder bore slowly become very slightly conical, and upside-down cone shape. Where the top rings run to will wear more at the top of the bore, than the well oil soaked bottom end. Eventually, the cylinder will need re-boring and new pistons fitting, and/or re-sleeving. You may have seen this bore-wear as a ridge about a quarter of an inch down, with the cylinder head removed. You can feel it with your finger nail. it is quite normal wear, but when it gets too much, then a rebore is the cure.

Now, you have to imagine the engine is buzzing away, you are driving along at 45mph, and the engine is worn but otherwise good. There is about 45-50,000 miles on the engine, and occasionally you get a puff of blue smoke upon starting the engine, (showing the inlet valve guides are worn) and manage about 400 miles per pint on a normal run. As the piston goes up and down the bore, and there is now a good five-thou' wear in the top of the bore, (giving a 0.0025" ridge) the piston rings will have to expand and contract that tiny five thou. 0.005" is five thou', but this is a diameter, as a circumference it is more like 0.015", and that is how much the piston ring gap will have to open and close as they rise and fall. At your normal cruising speed, this will not be too much of a problem. in a new engine the rings do not open or close at all, but they are made to be sprung into the bore to accommodate this eventual problem of wear. On all the 'strokes' of the piston but one, there is a pressure above the piston that assists oil not getting upwards. But on the 'inlet' stroke there is almost a negative pressure as the piston is pulled down by the crankshaft, sucking in the air and petrol mixture. This pressure is below that of the crankcase, and will assist oil to get up past the rings into the combustion chamber.

Now, at  45mph this might be acceptable, but one day you go for a good fast run up a motorway, and keep at 55-60mph for a couple of hours. Then you pull into a café for a break, and being a good driver of an old MG you check the engine's oil level. That is when you discover just what ring-pumping can do, as either you need a longer dip-stick, or some more oil very quickly. Being an experienced driver, you carry spare oil in the boot, so you top up the sump with two pints, and then realise you have been doing just 55 miles to the pint. You continue your journey, at a more sedate 45 mph, and upon arrival after another 100 miles, you check the dip-stick. it has hardly moved, you might have used a quarter of a pint. Why the difference?

At the 45mph figure, then engine can still cope with the amount of oil being thrown around in the sump, the oil rings are working at their limit, but even so some oil gets past the rings. A new engine might use just a pint every 1,500 miles, so your engine's consumption at 400 miles per pint shows it is worn. When you increased the speed, you also increased the oil temperature making it much thinner, and the oil flow. The poor rings became swamped. As the rings now have to slide into and out of their grooves to cope with the slight taper in the bore, and they are also a bit sloppy in the groove, oil can get behind the rings. This is alright for oil rings as they dump their oil through holes in the skirt, but bad news for compression rings. Normally the oil-control rings keep the oil down to a level that is sufficient for lubrication of the two top compression rings, and the piston's skirt. But if the oil gets hot and very thin, and there are masses of oil about, the worn oil rings will be unable to cope, and oil will get to the compression rings in a much larger quantity. The fact the oil gets behind them, and they slide in and out a few thou as they rise and fall in the cylinder, this actually helps to 'pump' the oil up to the combustion chamber. Now this is a tiny amount each time, but as you now know, those pistons go up and down an awful lot of times. Ring-pumping is a result of a worn bore, worn rings, worn ring grooves, and hot thin oil.

Quite a large number of drivers are unaware their engine is thus worn, and that it is quite a normal thing. Side-valve Ford engines of the 1940's and 50's suffered this fault very badly, and after just 30,000 miles required a rebore. The cast iron the blocks were made of, was poor quality, and like all mass-produced engines of those days, the cylinders are bored directly into the cast iron, Fords, Morris, MG, Austin, etc. So your XPAG engine perhaps needing a rebore at 80,000-90,000 miles is actually quite good, (providing you have changed your oil and filter regularly). As engines age, you have to be prepared to accept a slowly increasing oil consumption.

There was a time you could purchase piston ring kits that were laminated. Whilst the top compression ring was solid cast iron, with a groove cut in it to clear the ridge at the top of the bore, the other compression ring was actually three sprung-steel coils, that not only expanded to grip the groove, there were three segments rubbing the bore. The oil rings were two segments with a wavy, corrugated spring holding them apart. This permitted much more oil to be scraped off the bore and passed through the holes in the skirt. One firm that sold these kits was 'Cord Piston Rings'. They were only a temporary cure, but did reduce oil consumption. Today, many engines have these segmented oil-control rings fitted from new.

Worry and Stress

'I have recently brought a 'T' series, why is its XPAG engine so noisy? It performs well and uses a little oil and has the usual oil leaks."

That question is a compound of one of the most common I get, usually by email. it often comes from some one returning to the 'older car scene' after years of driving modern cars. The answer is that the modern car has spoilt the questioner with its good door seals and steeply raked windscreen getting rid of nearly all wind noises. The sealing of the hull and its design along with good soundproofing also masks any mechanical noises. To help along with this, many modern engines use over-head camshafts running with hydraulic tappets, all driven by a rubber covered steel belt. So straight away there is no tappet clatter or chain noise; because it is the valve gear of the XPAG that causes most noise. it is a very proud over-head valve train and it lets everyone know it is there. Your modern cars hydraulic tappets are expanded by the engines oil pressure to take up virtually all the clearances, so it runs without any gaps for sloppy push-rods and cam followers to bang about in.

So the XPAG is noisy, like all the other OHV engines of its day. The side-valve engines had fewer gaps between its camshaft and valve, and it was all buried down the side of the engine, so little 918cc Morris Eights sounded like sewing machines. The XPAG coming from the Morris family of engines, had a thin pressed steel rocker cover that can almost act as a sounding board, and it did not prevent noise from getting out. The simple fact that a OHV engine changes the direction of its actions through 180 degrees from the cam lobe to the valve stem does not help.

The noise is far worse in the MG saloon cars, any YA or YB has its noise trapped in its cabin, where as the T series and the YT with their open cock-pits are much quieter until wind noise becomes a problem. A T series with its hood up and side screens fitted is quite a bit noisier than when open.

There is only a wooden floor between you and the road, and a single steel sheet between the cab and the engine bay. So as that valve gear wears, the noise level rises. Adjusting the tappet clearances helps, but do not be tempted to close them up below the .019" or .012" depending on your camshaft type. The gap is part of the design: it permits oil to get between the various ends of push rods and rocker ends, as well as under the most highly stressed bit of the engine, the thin line of contact between the camshaft lobe and the base of the cam-follower, (called a 'tappet'). The later '12-thou' camshaft has 'silencing-ramps' built into the lobe. (See earlier article.).

Wear will cause the tip of the case-hardened camshaft lobe to wear, and this eats away the underside of the tappet, eventually causing it to concave and break up. The tappet also gets a lot of thrust in the direction of rotation of the cam, so it wears its hole oval, (you can get oversized +.010" tappets, many Gold Seal engine have them already). The oval hole with its sloppy tappet is a major cause of clatter, and no amount of adjusting the gap will cure it. it is very like piston-slap, but at half-engine speed. The ends of the push rods work loose, and cause more noise. But the item that is easy to change and will remove lots of excess noise, is the rocker shaft. it gets very badly worn on its under-side with the action of the valves and camshaft shoving upwards twice each cycle. it is also the last place to get any oil on starting up a cold engine.

Worn pads on the rockers, worn shaft bushes giving lots of side play, and the tiny camshaft bearing surface all contribute to the noises. The rocker pad has to be stoned to the correct 'arc' so it runs on the tip of the valve stem accurately. Get this wrong and you will cause the pad to shove the stem about sideways, and then wear out the valve guides. The guides can also cause some noise is they are worn, but heavy oil consumption on the over-run and high crankcase pressures on accelerating blowing out oil will indicate this problem. Worn pistons and bores lead to very high oil consumption at speed, (see earlier article on ring-pumping).

There are lots of other culprits under the bonnet that cause noise, a very powerful one is any carburettors that have no air-filters fitted. Pancake air-filters do little silencing of the intake-air, and that is why the Y saloons have a large intake 'silencer' above their single carburettor. The fan will roar away at speed, it very inefficient flat-spade like paddles bashing the air stupid as it pulls it through the radiator. Worn and cold engines will display piston-slap if run at too low an rpm in gear. This will mostly disappear once everything warms up to its running temperature. A badly worn camshaft lobe will make a sound like a diesel engine idling, and has fooled some into thinking a big end is on the way out. A worn timing-chain will clatter about at idle. The vibrations of the propeller shaft spinning away inches to your left ( or right on LHD cars) cause drumming. This can get quite bad if a universal joint is worn causing the shaft to spin out of true. Follow a few T types about, and you will soon see those with out of true wheels, or poorly fitted tyres that can cause vibrations.

Though whilst gearboxes and axles can cause noises, it is by far the faults of the valve gear that produces the most common racket your ears perceive. Having enjoyed the silence and reliability of a modern mechanical clone, going back fifty or more years to a very individual old MG can cause one to re-examine life. Suddenly there is something to worry about, is that oil pressure OK, what was that noise, is that vibration a fault, how much will it cost to fix? And so on and on. When you go out in the MG you are probably driving your partner to distraction with your worry. There is no need to, as all old MGs have an infallible system fitted that helps you source faults. it is the rear view mirror: look into it after each odd noise, if nothing fell off, keep going.

Oh yes, and a XPAG that has no oil leaks has an empty sump. Like many animals, old MGs mark their territories with scent, they use old black engine oil.

XPAG Oil System

(You will need the Workshop Manual  diagrams for this article.)

The Basics.

Of all the subjects I get requests to answer, there is one that regularly raises its head. it is one that bemuses me as the actual system it refers to is very basic, but seems also so capable of offering a multitude of differing symptoms. There also seems to be a lack of understanding of the basic physics of the rules this system has to comply to. The question I refer to is that old hoary subject of oil pressure. No doubt I am going to repeat myself in this mini-article, but I think it is worth it to give some sort of reference for others to use.

The basic physics I refer to is that of the resistance of the oil to go round the engines oil system. The designer will work out the correct running clearances of the relevant bearings, the amount of oil they need individually, the amount of oil needed for splash-lubrication, and what areas need an oil flow just to cool an item. The oil pump will be designed to give a flow well in excess of this, and the gear-type pump fitted to the XPAG engine can shift about 30 gallons an minute at 1000 rpm. From this you will gather the pump could empty the 8 or 10 pints from the sump in a few seconds. This will not happen as the oil system has its own built in controls as we will see. The reason the oil works at a pressure is simply because it has to be forced to flow through the engine, and the resistance of the small running clearances in the bearings create the pressure. The designer selects a suitable pressure that will mean all parts of the engine will get fed sufficient oil for its needs. On the XPAG this is 50psi, but this is displayed on the gauge only as an indication and is a measurement of the oil gallery pressure only.

Now we will take three engines and compare them. The first will be a brand new engine with all running clearances correct. The second will be a well looked after unit but with 60,000 miles use. The third will be a run down 100,000 mile unit, well worn and in desperate need of reconditioning.

1) A New Engine.

The first engine will run when at its normal running temperature with oil pressure of 50 to 70psi, as that is what the 'system pressure relief valve' is set to. This is a ½ inch ball bearing held against its seating by a spring, and lives in the end casting of the pump. it dumps excess oil directly back into the sump. This engine will have at least 50psi at idle rpm, and 50psi at 30mph in top gear.  The 30mph test at 50psi with the engine at its proper working temperature is the one to worry about, as irrespective of any other pressure Readings, this is the one that indicates the general condition of the engine. Because this 'new' engine has no worn parts, the 'system pressure relief valve' in the pump's end cover is in control. it will be relieving oil back to the sump all the time, simply because the oil pump is producing so much flow. in other words, quite a lot of the oil the pump moves goes straight back into the sump, only a percentage goes into the oil galleries. The reason for this is in the next paragraph.

2) The Well Looked After Older Engine.

The second engine will have wear, there will be quite a lot of wide gaps in places like rocker bushes, slightly oval main and big end bearing journals, worn camshaft bearings, and the pump itself will have wear. Oil pumps have to use unfiltered oil. When the engine was new, it had no problem maintaining the 50psi at 30mph engine hot running test. As this engine has been well looked after, it too can still give a 50psi Reading on the oil pressure gauge at 30mph in top. But the difference is, now very little oil is relieved back into the sump, as the spring under the ball bearing senses the need for more oil to compensate for the wider gaps everywhere. its function is to maintain a running pressure of at least 50psi, so it diverts more oil into the gallery to compensate for the worn, wider clearances. So the oil pressure gauge makes the engine appear as in as good a condition as the new engine. On this older engine, the oil flow is considerably higher than on the new engine. This has other side effects, as the piston rings, now also worn, have to try to stop the higher flow of oil from bearings spinning around in the sump, getting past them into the combustion chamber. So this engine uses more oil that the new one. Valve guides will also be worn, as well as the rocker bushes. More oil will get up into the head and valve gear, so again oil has more chance to be sucked down inlet valve guides, increasing oil consumption. it will be very noticeable how oil consumption will increase markedly as the car is run at high cruising speeds, simply because so much of the oil is going round the system. People following such a car will be impressed with the blue smoke from its exhaust on the over-run.

3) The Old Worn Out Engine.

The third engine will display all those old age problems. The pump will now be struggling to get sufficient oil out into the galleries. Due to few oil changes during its life the gears of the pump will be badly scored, permitting oil to escape backwards inside itself. The delivery flow into the oil gallery will still be very high, as there will be little resistance by the worn areas. With this engine at its running temperature just ticking over, the worn oil pump will not be able to get sufficient oil flow to build up any great resistance in the worn bearings. So the oil gauge will more than likely hardly not read any pressure at all. But note that oil is still flowing. The system pressure relief valve will be nearly closed. Sometimes it cannot fully closed as the seating will be pitted, the ball bearing itself grooved through use, and the spring coils worn thin by rubbing on the walls of its cage. The worn spring will make the system control itself at a lower pressure as the spring is weaker. This makes things worse as it is like having a leaking valve in your heart, the valve will let oil back into the sump by not seating properly. At the 30mph in top test, the oil pressure gauge may get up to around 30psi. This is where the bodger gets to work, and puts a washer behind the spring to increase its working pressure. A new ball bearing tapped onto its seat will reduce the leakage rate. There is now a chance that at 30mph in top that oil gauge will read 50psi. masking any wear.  This can be accomplished as the oil pump has such a huge capacity to shift oil. This old engine has become almost awash with oil inside, with it gushing out everywhere. The unsuspecting buyer of this car will only become aware of its poor engine when they check the oil consumption, and the general clatter. if they are foolish enough to drive it at any speed for any length of time, the crankshaft will run a bearing simply because the oil will escape via another easier gap in another bearing, starving others.

System Relief Valve.

This lives in the end casting of the oil pump, behind a big brass hexagonal plug. it is simply a ball bearing held by a spring against a seating sleeve, in a mazak guide. it is set to operate between 50 and 70psi when new. Whilst the gears in the oil pump will produce masses of oil, this ball valve will control the delivery pressure into the system. When new a lot of the oil gets sent back to the sump all the time, but this excess oil diminishes as the engine wears and gaps get larger. When the oil is cold the pressure will be a lot higher, but will drop down to its normal running pressure once hot. That is why the handbook says, '50psi at 30mph in top gear".  With a good engine, but a worn one, at idle rpm, on a hot day after a fast run, with a really hot engine and oil, you are NOT going to get 50psi. More likely 20-25psi, but as long as it rises to about 50psi at 30mph in top, there is not much to worry about. My own car with 64,000 miles, and a 1963 Gold Seal engine with about 40,000 miles on it, I get 45psi hot on long runs at 30mph. it never alters. A much newer engine might give 60psi under the same circumstances.

The spring behind the ball bearing often gets a bit of assistance from an extra washer, from people selling cars, to mask engine wear.

Oil Pressure & Oil types.

The oil pressure is also very dependant upon its temperature and viscosity. The XPAG engine is designed to run on SAE20 (thin) in winter and (thick) SAE30 in summer. Today this is equivalent to a 20/50 multigrade that is for all year round use. Running the older worn engine on thin modern 10/30 or 10/40 will seriously affect oil pressure on both the 60,000 mile engine and the worn out unit. it is highly likely that at idle rpm with a hot engine there will not be any Reading at all on the oil pressure gauge. The simple reason for this is there is virtually no resistance to the oil flow from the pump, when using such thin low viscosity oil. Conversely putting thick oil into the sump will certainly boost a flagging oil pressure, but may well cause damage internally. But even this was though of by the designer. The methods of manufacture and the then current engineering practices, as well as the metals used dictate the type of oil suitable. To put a modern, semi-synthetic low viscosity oil into an engine designed in 1937-38 is utter folly. That which does not leak out will be burnt by getting past the rings and valve guides.

The 'Pump By-pass Valve' (The Emergency Feed.)

Hidden inside the oil pump itself there is a 'safety valve'. This 'pump by-pass valve' discharges any excessive pressure direct into the main oil gallery. Note the 'system pressure relief valve' controls the running oil pressure, and is working all the time; but the 'pump by-pass valve' will probably only work a few times in the lifetime of the engine. its pressure is set at just 7psi, and is simply there to protect the engine if the oil filter blocks. it also relieves excessive oil pressure inside the pump. Gears meshing together on very cold thick oil can be broken.  For instance on a very cold morning with the oil very thick, it is possible to get very, very high pressure between the gears in the pump itself. This can break off a gear tooth, not an ideal thing to happen. So the pump by-pass valve will let the high pressure get away safely. True, it is a belt-and-braces affair. 7psi seems a low pressure, but the oil filter has about a 3 to 5 psi pressure drop across its element. This is normal, but as the element blocks up with sludge the oil flow suffers. So the 7psi is the difference between the oil feed to the filter, and the feed from the filter into the main oil gallery. Few people seem to know this valve exists, and it can only be seen with the pump removed. The main oil gallery is the internal passageway cast into the engine that runs the full length of the block, alongside the camshaft.  The reason the valve relieves into the gallery is simple, it by-passes the oil filter so at least oil will get to the bearings albeit unfiltered. Again, I stress this valve very rarely works unless you never change the oil filter. it is an emergency valve. On later SC2 engines this valve's location changes it usage and the by-pass filter is inside the filter housing. if any dirt gets onto this valves seating, it will be indicated by very high pressures because the pump can leak directly into the oil gallery (a high pressure with the engine hot, not the usual high pressure on starting with cold, thick oil). Very high oil pressures will damage white metal coated bearings by literally scouring the metal away.

The by-pass valve has already been mentioned. its main function is to sense when the oil filter element is blocked, and to then open to feed unfiltered oil directly into the main oil gallery from the pump. it is set at 7psi, this being the designated pressure difference across the filter element as being too high, suggesting the filter is blocked. A sign of this happening is a rise of oil pressure on the gauge, when hot, for no apparent reason. it is an emergency valve and on good engines has probably never worked unless the pump gears have had very high cold-oil pressures, where it again will open to protect the pump.

On the SC2 engines with the integral oil filter, the pumps by-pass valve hole into the main oil gallery is used for the main oil feed from the oil filter. The whole oil filter element is the by-pass valve now, as it sits on its own spring. The spring holds it against the oil feed end from the pump. if the element becomes blocked, the pump pressure will force the filter element back off its seating, and oil will flow around it. Again the spring is set at about 7psi, so if the oil pressure AFTER the filter drops more that 7psi below the pressure BEFORE the filter, it will lift off its seating.

The Oil Pump.

The oil pump is driven from the camshaft, itself driven at half speed from the crankshaft by a chain from the front of the engine. Assuming the sump is filled to the correct level with the correct type of oil, when the starter motor, (or when the starting handle is used) turns the engine, the oil pump will work. it has a pair of long meshing gears, and the oil is drawn around the outside of these two gears, not between them, as oil is incompressible. As long as the internals of the oil pump are wetted with oil, (a 'dry' pump will not 'lift' anything) the action of the rotating gears will 'lift' the oil from the sump. There will be no 'pressure' until the pump is full, the oil filter is full, and all the oil-ways are full. As the pump turns, it 'sucks' the oil up through the sump's mesh filter, up the internal oil-way in the sump, to the pump. Normally once the pump is full, and the system is full, it will not drain down again, so the next time you start the engine oil pressure will be instant, or as instant as the gauge will permit. The physics of the suction side of the oil pump should have already shown you there can be problems. For instance it is far easier to suck air than oil. So there must not be any leakage paths between gasket surfaces in the sump, or the sump to block face. Also, mesh sump filters can become blocked with sludge, as can the actual oil-way to the pump. This is one reason for regularly changing your oil, and only using good quality oils.

 As the pump is about six inches above the sump oil level, there can be problems priming a newly fitted pump. Priming means getting the oil up to the pump and filling the galleries. An old trick is to assemble the pump full of Vaseline, working on the principle that as the Vaseline is moved out of the pump the oil will move in. Any air spaces left will cause problems, as air can be compressed. This is an excellent reason to always turn a rebuilt engine over by hand with the starting handle and the pump to filter exit pipe undone, until oil comes out. Or if you have the later oil pump with the integral filter body as part of it, till oil comes out of the banjo-bolt that feeds the rockers. You have then 'primed' the engine. A good few minutes of further spinning the cold engine over by hand will ensure oil has got through to everywhere. I always assemble engines using STP, and fill all oil-ways after cleaning them out, with fresh oil. Late engines have a priming plug fitted on the pump body. All you need to do here is spin the engine over until oil comes out. if it does not, then fill the pump with clean oil via this plug, and try again. NEVER run a rebuilt engine until you know oil is being delivered to the vital parts, and to check look at the rockers. Once oil is up in them, all other areas will be well soaked.

The Oil Gauge.

The oil pressure gauge is a simple device using a bourbon tube that opens out as pressure increases. The tube has a little gear rack on it, and this engages with a gear to which a needle is mounted. The needle then wipes a face with the relevant pressure Reading on it. it is fed by a thin copper tube from the lower banjo-bolt on the rocker feed pipe. if you foolishly connect it to the top banjo bolt you will get a lower Reading, as the rocker feeder pipe acts as a pressure-reducing part, restricting oil flow to the rockers. it does this along with the small holes in the banjo bolts, on later engines made even smaller. When the engine starts, the oil pressure is pretty instant. But the gauge takes time to react, and it is only an indication of the pressure at the rear end of the main oil gallery, where the rocker oil feed is taken from. Oil pressure up inside the rocker shaft is only about 15-20psi, when that inside the oil filter may be 50-55psi. The gauge will read 50psi, as that is what the designer worked out. Now, you should have spotted an anomaly, as I told you the 'system relief valve' worked at 50psi. Well, to give a Reading of 50psi to the oil pressure gauge the valve actually works at about 55-60psi, as the oil filter has quite a pressure-drop across the element. This represents the work required to 'filter' the oil, and every item in the system that has an oil flow after the pump will cause a pressure drop. Hence the reason for not measuring the oil pressure from the wrong end of the rocker feed pipe. You cannot have failed to notice that on a cold day, the oil pressure gauge can take quite some time to read. This is because the oil is cold and the narrow pipe to it takes time to build up its internal pressure. But once the engine is hot, the gauge will react to pressure changes very quickly, like the worn engine at idle rpm with no Reading; blipping the throttle will have the needle jumping up the dial quickly.

The oil pressure set by the factory when the engine was new also covered up another problem. That is one of production tolerances, where one engine may be built tight, another at 'blue-print' clearances, and yet another very loose. All will be within the production limits, but if the system pressure relief valve was not adjustable, all would give different oil pressures. This is one reason why the workshop manual will quote a hot oil pressure of between 40 to 55 psi in some cases. At Morris Engines where the XPAG was assembled, there would be a selection of springs of various compression strengths. The engine would be spun over on a machine and the oil pressure noted: if found too low, a stronger spring may be fitted, or a slightly different length seating sleeve.

If the 'Y' was fitted with an oil light that only came on at 10psi as in modern cars, and no oil pressure gauge, what would you find to worry about?

Engine internals.

The oil is fed from the oil filter into the main oil gallery, and then via drillings to the rotating assemblies of the crankshaft and camshaft. The camshaft gets each of three bearings lubricated, where as the crankshaft gets the bigger slice of oil. This needs the extra as not only do the three main bearings get pressure fed, the crankshaft has internal drillings to feed the big-ends. The big end also spray oil up the cylinder bores to both lubricate and cool the pistons. Some oil is bled off the front camshaft bearing to the Reynolds timing chain tensioner, to help its spring and to lubricate the chain and sprockets. The rockers get a limited feed through a drilling inside the shaft, and some gets sprayed out of the rockers to cool and lubricate the valves. The rocker oil then runs down the push-rod holes to lubricate the camshaft followers. The oil thrown out by the big-ends splash-lubricates the camshaft lobes and the follower lower faces.

It is not unknown for amateur engine assemblers to fit a reground crankshaft that is 0.020 thou undersize, with shell bearings that are only 0.010 thou undersize. The running clearance is then increased from 0.0005 + or – 0.001 thou to 0.010 thou. (i.e. ten times the correct clearance.) This results in a very noisy engine and no oil pressure. invariably the crankshaft is ruined by the hammering it gets.

Old Age Problems.

Most of the 'Y' types fitted with the XPAG are now over 50 years old. Few will have their original engine fitted, un-rebuilt. There is also the problem of various differing oil pumps and oil filter arrangements. On the SC2 engines the pump by-pass is omitted, and opened out for the oil filter to feed direct into the oil gallery. This is the oil pump with the filter case cast integral that has the by-pass valve inside the filter.

From what I have already mentioned, the majority of faults can be traced. One that often crops up is low oil pressure on a re-built engine. As I cannot see the engine, and do not know what work has been done, it is impossible to diagnose the fault. I can only advise. So here follows a list, starting with the basics.

NO OIL PRESSURE.

• No oil in the sump
• Gauge pipe not connected.
• Gauge needle stuck.
• Pump assembled dry.
• System relief valve spring broken.
• System relief valve ball stuck open.
• System relief valve assemble incorrectly.
• Pipe to gauge broken.
• Rubber hose in the gauge pipe blocked.
• Pump needs priming.
• Air leak in the suction side in the sump.
• Blocked sump gauze filter.
• System relief valve seating sleeve missing.

LOW OIL PRESSURE.

• Worn engine bearings.
• System relief valve spring weak.
• System relief valve ball bearing pitted.
• System relief valve seating worn.
• Too much end-play in the oil pump gears.
• Worn oil pump gear faces.
• Oil too thin, wrong type.
• Wrong bearing shells fitted, too big.
• System relief valve seat re-cut, shims required for the spring to correct its length.
• System relief valve spring coils worn, weakening the spring.
• System relief valve seating sleeve missing.
• Partially blocked suction pipe-ways.

FLUCTUATING OIL PRESSURE.

• Dirt on the system relief valve seat.
• Air leak on the suction side.
• Oil filter element about to block, By-pass valve operating intermittently.

HIGH OIL PRESSURE.

• Oil filter element blocked, by-pass valve open direct into the oil gallery.
• Oil of too thick viscosity.
• Bearing clearances too-tight, ( they will soon seize up or run.)

My Oil Pressure is Low on my Newly Rebuilt Engine.

You should have found your problem whilst reading all the above, but to recap here are a few hints. Oil pressure is the resistance to the oil getting through the narrow running clearances of the engines bearings. If the pressure is low, somewhere has too big a gap, OR there is a leak. Double check the crankshaft has the correct shells fitted for its re-ground diameter. Checks the camshaft bearing are in good condition, as well as its bearing surfaces. Use a micrometer to do these checks, or plastigauge. Checks the oil pump is all there and correctly assembled, and that the various springs are not worn or weak. The most common item to get lost is the seating sleeve inside the system relief valve. This sleeve and its ball bearing must be PERFECT, no grooves or nicks. Check the end float of the gears inside the oil pump, about 2 to 3 thou is sufficient. if it is above this, you have two choices, either lap-in the end of the oil pump casting to make the whole body that bit shorter, to give you the 2-3 thou; or buy two new gears. if the gear teeth are scored, buy new anyway.

If all the above proves to be in order, and you still have low oil pressure, do as the factory did. Fit a stronger system relief valve spring.

Save The planet. (Reduce Oil Consumption.)

When 'international' motoring legislation started to target the pollution the car engine produces, it was not all bad news. One thing that very quickly became apparent was that well sealed and properly vented engines did not leak oil. For years the British motor industry used very basic venting systems, and left the poor owner to cope with an engine that was destined to leak and consume oil after a few tens-of-thousands of miles. Today, there are tidy, little all-aluminium, multi-valve, over-head-camshaft engines with sealed breathing systems that run over 100,000 miles, without leaking one drop of and hardly consuming any oil. The sealing of the cylinder bores, and the valve guides, makes the oil seem unnaturally clean for considerable periods. Where as a well used XPAG's dip stick will tell you of the huge amount of carbon the oil is carrying after a couple of thousand miles, by its thick and very black constituency, today's plastic dip-stick end will appear almost  clean. So how is it done and can we 'transfer' any of this modern engineering to our rather elderly engine?

Well, not much can be used, as the tolerances and seals used are for modern metals and materials. Our XPAG is basically a Morris saloon car engine, with the cylinder bores of grey-cast-iron bored direct into the casting. The rope seal at the front can be updated to the TV/Wolseley 4/44 neoprene sprung-lip-seal, and the rear scroll seal fitted with a rather expensive after-market sealing system. The way the modern engines keep their oil in is to keep the crankcase pressure below ambient, that is, below the normal outside air pressure. This means any leak in theory will be into the engines crankcase, not out. This is done by using the inlet manifold and a controlling system to 'consume' any excess gasses. Again this is not practicable on our engines: he venting system is too crude. But, one of the methods of reducing oil consumption, and stopping burnt oil getting into the exhaust system hence reducing the pollution produced, is to improve the valve stem sealing. On modern cars catalytic converters are fitted, either two-way on older carburettor cars, or three-way on fuel injected cars. Burning oil can coat these internally with carbon, and so reduce their efficiency.

It is not only the mechanical engineering that has improved. The oil one buys today is a far cry from that sold in the 1950's. The straight SAE 20 or SAE 30 oils of those days soon broke down. Multi-grade 20/50 is the best to use in an XPAG today. This oil in itself is a very advanced bit of engineering, but be warned that the thinner semi-synthetic oils meant for modern engines will not suit. Oil is so good today that even the cheap-reclaimed oils from supermarkets is far better quality than that used originally in our 'dirty' engines, changing the oil and its filter is required very regularly, the oil possibly as often as every 3,000 miles., (unless you have a filter system that uses a modern element).

Oil also reduces the octane rating of petrol, so if your engine uses and burns oil, you are more likely to suffer 'pinking' if you have raised the compression ratio. if it is still the standard 7.3 to 1 ratio, designed for post-WW2 pool-petrol of about 80 Octane, oil burning will not make much difference.

On our engines, the oil is stopped from getting into the inlet manifold by a shroud around the valve stem, and a tiny 'O' ring seal under the valve cap, (see diagram). The 'O' ring seals, the cap, the valve stem, and the collets as one. This turns the cap into a 'table and no oil can run down the stem and into the guide, instead it runs off the 'edge of the table'. But as the inlet valves wear their guides, and there is a fair drop in pressure in the inlet manifold, oil inevitably gets sucked down the guides as oil-mist. A bit of crankcase-compression caused by worn rings letting combustion gasses past will assist the escaping oil. The exhaust valves do not suffer this, as there is no where near the same 'depression' in that manifold. If anything the exhaust can blow 'up' these guides if badly worn. A study of a more modern engine will reveal that inlet valve guides are fitted with seals, not the stem and cap. The seal affixes to the top of the guide, and the stem runs inside it. This is very effective, in fact so effective if fitted to a XPAG exhaust guide the exhaust valve will soon seize-up through lack of oil. So do not fit such seals to the exhaust valve guides. How ever, fitting them to the inlet valve guides is very effective, and will make a noticeable reduction in oil consumption.

So which seals do you need? Those intended for the EARLY version of the 1275cc BMC engine fit nicely. These are simple flexible neoprene caps, (see sketch). Later seals have a steel outer-case and this will not let the seal slide over our guides. Seals will be found in Mini 1275cc, MG Midget 1275cc, Morris Marina 1.3, and Metro 1.3 gasket sets. They can be purchased separately at some motor factors.

So we can apply a little of today's technology to the XPAG engine. it may not be ground-breaking technology, but it will do its bit to reduce pollution, and save your oil.

Y Type Reliability

I have now been on quite a few runs with others in Y Types, and have been dragged into diagnosing the various faults that the cars have developed on that run. So after a few runs you can get quite a wide perspective of the most common things that go wrong. Be well aware that when your car was built, the company only expected it to last about 5 to 10 years, at the most. So here we are running about in ancient vehicles, many well over 60 years old. is it any wonder that some of them will break down? Your car is a bit like a woman, they like lots of attention. ignore them and they play up.

Ignition.

By far the most common fault will be with the ignition. The things that seem to go wrong are wires coming lose on the coil, or inside the distributor. This gives a hard to find misfire. Plug leads that are well past their sell by date also soon play up once they get really hot, the large amounts of oil around will cause enough dirt to stick to things so the spark will go everywhere but to the plug. Plugs may well oil up if it is a hot day and the oil very thin. More oil will get past rings and down valve guides. A set of clean plugs carried as spares helps to speed up a cure. Wires that sit on oil pipes, or other metal items, can chaff through and short out, the most common one being that from the coil to the distributor. An odd one was once the corrosion that grew under the fuse that supplied the ignition switch. As soon as any heavy current was drawn, the engine stopped. Cleaning the fuse box clips cured it, but it took some finding! Loose wire connections on the back of the ignition switch caused one very intermittent engine misfire. Overheated condensers will stop working and earth themselves. This stops the points working. But when it all cools down the condenser will work again. This fault has also often occurred on Y Type runs, and questioning the car's owner soon shows up that the condenser is often a very old one. Once I had to change ignition points that were so burnt away I could not see how they ever worked. The owner just shrugged his shoulders and seemed ignorant they even existed.

Oil.

Oil leaks is the second most common fault. At the head of this list is the oil pipe that feeds the oil pressure gauge. if you are lucky it will leak at the instrument end, giving you a hot, wet and sticky left knee. If it leaks behind the battery box some oil might drip inside the car to warn you, usually over your partners new shoes. But the biggest danger is it breaking due to age hardening between the engine and the bulkhead. Here you slowly let the engine bleed to its death. A very good reason to glance at the pressure gauge often. The second leak is at the rear bearing housing area. All XPAG's leak here if they still have the scroll-seal arrangement. Many drivers seem to worry too much over this leak, but it can be a pain if it lets oil onto the clutch; the sign of this is clutch judder and a smell of burning oil, followed after a while by clutch slip. A quick temporary cure is to squirt a CTC fire extinguisher into the clutch, with the plate held open. Oil will be blown out of the breather pipe and out of the filler cap once the bores wear a bit. This is more annoying than dodgy. There has been a case of an oil pipe on the oil pump fracturing, this can only be through old age-age hardening-and stressing the pipe during fitting. Oil seal on the later engines where the filter bolts to the oil pump casting, the seal that the canister seats on can be blown out if not gripped properly. Again this may be because the old seal was rock hard and the owner assumed there was none fitted, so fitted another over the top of it. A leak here is a very fast way to wreck the engine, as well as to leave a very obvious oil trail on the road. Fast running on motorways for long runs (over 55mph) will cause oil to be 'ring-pumped' up into the combustion chambers, and a worn engine can consume its entire sump in a very short time. The cure is a recovery truck and a new engine.

Water.

Water can also leak out. Age will mean at least one core plug will be very thin, usually the one you cannot see at the rear of the engine, well below the battery box. Look out for rusty looking water runs from them all. Old heater pipes may crack open and leak, rubber hoses only last about five years before they begin to rot. The most common radiator hose to go is the huge top one. This pipe is shared with the big pre-war M.G.S. saloons, and millions of Morris cars, so finding a spares to carry should be easy. They get very brittle after a while, and with the engine moving about the hose cracks, most often just above the lower hose clip. The water runs down the engine to drip off the water pump. You assume it is the water pump seal that has gone, so you fit a new pump, only to find it was the ( much cheaper) hose. Old radiators can leak, again the tell-tale sign is a rusty water stain from the leaking areas. Holts Radweld will often act as a temporary cure, so carry a bottle. if you are really stuck the white of an egg dropped into the radiator may block the leak, but not if the system is a pressurised one. (The Y Types is not pressurised.) Again, carry water in case of any leaks.

Electrical.

Electrical faults are few, usually lighting problems if you have to drive at night. if you do a long over-night trip with all lights on, do not be surprised if the battery is pretty flat the next day. Many people are using 55/65 headlamp bulbs and bigger, when the dynamo can only just cope with 45/55. if the heater and wipers are used the dynamo cannot hope to cope. it is obvious you need to carry spare bulbs, and check them all often. Most electrical faults will be due to corrosion inside the little connectors all over the car, (i.e. slow trafficators.)

Brakes.

A few tales of sticking brakes have been told in the past. Again, most often this is because the system has been filled with silicon fluid but the old seals left in situ. But even normal hydraulic brakes can appear to stick on, usually on the rear axle. The fault will be inside the rear brake cylinder, where the 'second' piston that the handbrake uses, is corroded and sticking in its hole holding 'on' the shoes. A sign is a very hot rear wheel centre, this can be enough to blister the paint!

Clutch.

The clutch cable is out if sight so out of mind. it needs greasing often, and keeping in adjustment. it will always break at a busy cross road with traffic lights, in the pouring rain. Carry a spare or fit a rod from a TD/TV. For clutch slip see 'Oil' above.

Petrol.

Springs on carburettor linkages often break, a few elastic bands will get you home. Less often but more serious is a broken throttle cable. Carry a spare, you can make one from a bicycle brake cable in thirty minutes. Keep the points in the SU fuel pump clean, or buy a Burlen's solid-stare one. There are still Y Types out there with no insulation between the inlet manifold and carburettor, and a heat shield. Very hot summer days sitting in a traffic queue will soon 'boil' unleaded petrol. Once the carburettor and pipes are full of just vapour you will never re-start the engine. A temporary cure is to douse the carburettor in cold water, this might condense the fuel enough to get going. Again, you will be the centre of attention as you hold up hundreds of commuters with your Y Type blocking the road.

Many people are saved by other Y owners who offer oil, or plugs, or Radweld. Always offer to pay them for their item and thank them.

Safe motoring.