Technical


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Extract from November's Octagon Car Club Bulletin

Questions

  • After switching off the engine of my 'M' type I find starting very difficult. This is due to an excessive amount of fuel in the body of the carburettor. I believe this is a common problem. Is there a cure?
    Alan Fleet, Blandford, Dorset.

  • I've heard a number of people say that M-type wheel nuts tend to come loose, and have found this myself. Have others had similar problems and could confirm this habit?
    Philip Bayne-Powell, Normandy, Sussex.

  • In their answers about higher ratio rear axles several correspondents have mentioned the need for a more highly tuned engine. I wonder about the effects of increased power on the clutch. Does it cope easily or is there a tendency to slip as the power is taken up? If so is it possible to fit a tougher alternative?
    Malcolm Taylor, Huddersfield, West Yorkshire.

    Answers

  • Could a member please tell me what may be wrong with my TF? The whole dash board shakes horribly from side to side when I hit a bump. The car regularly passes a strict MOT test with all the steering joints checked. (No325)

    If only a few screws could cure scuttle shake. The source of the shake can be one of the following, any combination or all of them.
    Front wheels - out of balance
    Balance
    Shock absorbers - worn
    Get them rebuilt by a reputable company who know what they are doing and have the right tools for the job.
    Front suspension - wear in the trunnions and king post
    Replace with new parts and do not face up the trunnions and crop the spacer tube to fit.
    Inner Pivot - wear in the bolts holding the pivot to the chassis.
    Fit new bolts and check for wear in the holes.
    Set screws - may have been used to attach the inner pivot to the chassis. It is possible for the pivot to fret on the threads and create a clearance and hence shake.
    Remove the set screws and fit the correct bolts checking that the holes in the chassis and pivot are true.
    Bolts - holding the inner pivot to the chassis are loose.
    Tighten
    Tyres - are incorrectly fitted i.e. the threads are not true to the rim.
    Refit or replace.

    Scrimping on repairs and maintenance of the front suspension is dangerous. Fancy loosing a front wheel from your car at 60 mph in the face of oncoming traffic?
    A good friend had a terrible scuttle shake on his MGA which has the same front suspension as the TF. He replaced the shock absorbers, rebuilt the front suspension using special aviation bolts and had the wheels balanced off the car. But still there was shake. Only when he took the car to have the wheels balanced on the car did he discover that the tread of at least one front tyre was not straight. The tyre was changed - result - no shake.

    A thought. Many older M.G.s are brought and used by people with little previous experience of them or with engineering knowledge. Many are often unaware of the design and construction of old cars. Some, in my experience have never seen a fly-off hand brake and cannot comprehend a car with a starting button separate from the ignition switch, Thus, it is possible for parts to be wrongly fitted, wrongly adjusted, endagering those who use the car, At a recent M.G. event a car was seen with the engine mountings only hand tight. Did the coroner discover what else was loose and wrong?
    Similarly with parts. At Beaulieu I was amazed to see second hand trunnions for sale, clearly worn. No doubt they were cheaper than new but how do you value your car and your life.
    The moral is don't scrimp, buy the best parts and ensure that your or Neil the fitter in his Grateful Dead T shirt has correctly fitted and adjusted each and every part.
    Robert Marshall, Bath

  • There isn't a mark for 0 revs on the PA rev counter (and perhaps others too). The first mark is for 300 revs - approx. 5mph. Where does the pointer go at rest? (No 328)
    The needle of the rev counter should in fact be pointing at 300 rpm even when the engine is switched off!

    I have recently fitted an electronic speedo/mileometer that is intended for bicycles just to check the accuracy of the original 1930s technology of the P type speedo and was amazed to find that it seems to be accurate to within 2 mph right through the range; so presumably the revs are right throughout the range too.

    Incidentally these electronic speedos (available from any cycle shop) only cost about 15, take about two hours to fit and provide great motoring entertainment when one should be driving carefully looking at the road ahead. Not only do they give speed but, at the press of a button they give a reading of elapsed time, average speed, total mileage and - most foolhardy of all challenges - highest speed attained ever! All great fun and totally anachronistic and out of character on a traditional vehicle. Quite rightly they are not acceptable on VSCC or similar events.

    But Tom 5,500 revs in third? Is it really kind? Hardly surprising that the rev counter fell to pieces - perhaps it was trying to tell you something!
    John Buckley, Denbigh, North Wales.

    Tips and Comments

    Paraffin in Petrol
    The following first appeared in The Motor of 25th March 1913 and in view of recent comments may be of interest to members. On purely engine wear basis the dangers are quite obvious and I do not think our cars should ever see the stuff!
    "It has already been explained why a large admixture of paraffin has certain disadvantages, amongst which are those of difficulty in starting up and the usual faults of incomplete combustion, such as fouled-up plugs and a smoke exhaust. There is a still more serious disadvantage of paraffin which has not been, so far, touched upon, and that is its adverse effect on the lubrication of the engine. It is safe to assume that any paraffin that fails to be consumed during the explosion stroke will condense back into the liquid state, and in so doing will more or less dissolve off the film of lubricant from the surface of the cylinder walls and piston. This is bound to cause increased friction, as anyone who has given a cylinder an over-injection of paraffin at starting will appreciate if they have had to continue turning the starting handle. The fact is that paraffin has no lubricating properties, but is on the contrary, anti-lubricating in its effect. Owing to its great mobility, any condensed paraffin is certain to leak past the piston rings and run into the crank chamber base, and it is here that the greatest risk occurs. The gradual accumulation of paraffin will thin down the lubricating oil and greatly diminish its lubricating properties. The risk of a 'seize up' of connecting rod or crankshaft bearings must, as a result, be an ever present one: in fact, instances of this have already occurred, hence the need for a timely warning on the subject."
    David Berry, Yarm, Cleveland.

    Escort TF
    Last year my wife Elma and I took part in the South African M.G. Indaba Rally, whilst I was there I was privileged to ride in the 1500cc TF owned by Stuart Cunningham from Johannesburg. Not only was the car in super concours condition, it really did motor like the clappers, thanks to an MGA crown wheel and pinnion. But its most intriguing modification was a set of close ratio gears from a Ford rear wheel drive 2 door Escort which had been fitted into the M.G. TF gearbox casing with no visible external modification, not even to the gearchange or mountings.
    I recently wrote to Stewart enquiring on how the modifications were achieved. Here is his reply:
    "You must locate a Ford Escort Sports box, this is the 1600cc two door car, not the four door saloon, as the two door sports has the close ratio gearbox. It may only have been built in South Africa (Escort `Mexico' in UK).
    The Escort box has different lay-shaft cluster centres compared to the TF box, therefore it is necessary to make plugs to blank off the original lay-shaft holes and secure these plugs in the TF box with 'C' pins, then rebore the housing for the Ford lay-gear to suit the larger centre spacing of the Ford Escort gears. The improvement I made to the TF box was to replace the gearbox rear bearing and spacer by making up a new bearing retainer and fitting a larger needle roller bearing and oil seal.
    The gear change and selectors need no alteration."
    Since the modification the TF has completed many thousands of miles including a rally to Maputo in Mozambique. It was also one of the M.G.s that raced the "Blue Train" from Johannesburg to Cape Town whilst Elma and I were feet-up and letting the Puffer take the strain.
    In his letter Stewart did not mention any modification to the clutch but I seem to recall that during conversation he mentioned a Ford clutch plate. I have not checked but I suspect that any of the rear wheel Escort gearboxes could be used the difference being the gear ratios.
    Stewart has an interesting collection of vehicles, they include a Lenham Sprite with an eight port cross-flow head, a genuine Sebring Sprite raced by his son, a 1934 Austin Nippy with a 750cc Brooklands engine and a 1930 OHC Manx Norton International, which he rides. All of them restored to perfection. If any member has a go at carrying out the modification and runs into difficulties I will be pleased to let them have Stewart's address.
    Cyril Mellor, Kings Bromley, Staffordshire.

    NDT Testing
    Having been involved in the engineering industry for many years I have access to the current NDT yearbooks which, amongst other things, list the companies which provide inspection services. I will be happy to pass on to members who care to `phone me (01332 690805), the addresses of companies in various parts of the country. Alternatively, I can arrange for testing at a nearby company but would have to pass on the charges.
    David Barnes, Chellaston, Derby.
    (David has also provided me with copies of relevant addresses. MT)

    NB Thermostat
    During a telephone conversation with William Opie who, inter alia, owns an NB we discussed the length of time it takes the engine to "warm up". William told me that he had recently fitted a thermostat and was very pleased with the result. I have now done the same to our NB and am also delighted. The thermostat is used in a Renault and fits neatly into the top hose of a NB. The one I have used is Quinton Hazel Part No QTH 144, rated at 83 degrees. Instead of taking several miles to warm up and in winter only doing so if an appropriate piece of cardboard was placed in front of the radiator, our NB now has a temperature of 83 degrees within about one and a half miles and the oil temperature also rises much more quickly (much less engine wear!).
    The thermostat will need a small hole (about 1/8") drilled to act as a bypass and is then simply pushed into the top hose at the water manifold end. It is good fit but to make sure it cannot move I have secured it with a jubilee clip, it has a convenient lip. The car has suffered no side effects, is no more prone to overheat than before and now runs with other 'MMM' cars with a similar top hose but it is worth mentioning that 'N' types have a water pump fitted and, although I can think of no problems, I have no experience of the effects of fitting to a car without a water pump.
    Peter Arnell, Dorking, Surrey.

    NA Starter Problem
    Whilst the Allingham NA was at the VSCC Brooklands Driving test I experienced a strange problem which at first puzzled me. The starter suddenly packed up so I had to keep the engine running or push start it. I at first blamed the starter but having changed to a spare, overhauled starter, found no improvement. I then checked the wiring and earth strap from the starter which were OK, so I looked at the starter button on the bulkhead. This was taken apart, cleaned up and replaced with no signs of any problems but still the starter would not work. I then shorted the leads across the starter button and it did work - so obviously the fault was in the starter button. This came off again and inside there is a double cup made of copper which is pushed into contact with a cast cooper cone. The cup had splayed out over the years and was not contacting the cone, the starter button could not be pushed far enough to engage the two because of the return spring and the bulkhead. I closed up the cup with judicious leverage and on refitting found that everything was working again.
    Philip Bayne-Powell, Normandy, Sussex.

    XPJM - The Undiscovered Treasure
    Treasure? undiscovered? Everybody knows about the XPJM. It was the Morris 10 engine, the ancestor of the XPAG, wasn't it? 1140cc not at all suitable for T-types, although some poor souls in the past, faced with blown up XPAGs, have put them into their TBs, Tcs and TDs in desperation. And then done their best to keep quiet about it. If the TB or TC owner is reluctant to open the left hand side of the bonnet you have reason to suspect that he a secret XPJM convert because he doesn't want you to see the shameful fact there is NO MG LOGO cast into his block!
    TD owners can be much more sanguine about the problem because the later TD blocks did not have the logo anyway, and TFs did not have it at all.
    Well, what's so good about this underpowered lump with its weedy con rods and spindly push rods? The good thing, oh scornful ones, is that it is almost exactly like an XPAG in all its major items, and as the XPAG becomes increasingly difficult to find and consequently more expensive, the humble XPJM can provide a very practical alternative.
    The XPJM can be bored out from its normal 63.5mm to 66.5mm, which, you will no doubt have spotted, is the bore size of the standard XPAG, pushing the capacity from 1140 to 1250cc. This is the first step in converting the XPJM into a credible T-type engine.
    The next thing is to dispose of the con rods and obtain a set of XPAG rods which are much beefier, though no doubt many engines which are not driven hard still retain the originals. The big end caps can be fitted to XPAG rods but the big end bolts cannot be re-used as they are too short. The crank and main bearing caps appear identical.
    The push rods on some XPJMs are rather like knitting needles and XPAG pushrods should replace them. The standard camshaft should be consigned to the bin and a TC camshaft substituted. XPJM sumps are various shapes, with bits sticking out at the side on some. They will suffice, but look rather odd on a T-type and I suspect that the oil capacity is less even than the early XPAG sumps.

    Once bored out then, the XPJM block is identical to a standard XPAG (except for the logo, and we'll come to that in a minute).
    The engine type number, cast below the front edge of the tappet chest, is usually 24144, compared with the early XPAG number 24146. I have also seen very early XPJMs with the number 22500, possibly pre-war?

    Early XPJM heads carry the number 22812, they differ from XPAG heads only in that the top edges are parallel, whereas the left hand edge of the XPAG is curved (anyone know why?) and there is no oil return hole in the centre of the head. Later XPJMs had the same head as early T-types, ie: the one with elongated water holes, number 22952.

    So it can be seen that the much-scorned Morris 10 engine can be readily converted to a perfectly serviceable replacement for an expired XPAG, and currently it is much, much less expensive to buy. In fact I do not know why T-type owner does not have one put by, just in case. Could it be the lack of the ubiquitous MG logo?

    Well for those who do not have the artistic MIG welding skills of our Swedish colleague Bjarne Bergengren (Bulletin No309, February 1996), all will now be revealed.

    Examples of that fine MG saloon the ZA Magnette have gone to the scrapyard by the thousand, many via the dubious 'sport' of classic banger racing. However, Possibly because an extremely attractive alloy casting, the air inlet manifold with its MG logo seems to have survived in considerable numbers and can be found at autojumbles for very little money. (I wouldn't pay more than a 'fiver').
    It is the logo which is of interest to us here, as in size and definition it is almost identical to the logo cast into the XPAG blocks. Get the drift?
    A few minutes careful work with hacksaw along the edges of the octagon will produce an MG badge that is not only similar in size to the desired object, but whose contours fit the block almost exactly! Strange but true. A quick dab of Araldite will secure it to the block when any gaps can be filled with Isopon or similar. Once your handiwork is rubbed down and painted only close scrutiny by an expert could reveal that your XPJM is not indeed its more sporty cousin. So there you are, an XPAG look-alike for peanuts. Don't delay, buy and XPJM today, before they get as scarce as XPAGs, or hen's teeth.
    Jake Wilson, Paignton, Devon.

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