Technical


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Extract from April's Octagon Car Club Bulletin

QA Technical Torque

A question in the January issue has produced a most interesting response from one of our regular contributors, Bjarne Bergengren. Theoretically, it should be possible to fit a catalyst to most petrol engines and Neil Cairns warned us in his article in Bulletin No328 (p18) that we are likely to have to adjust to the idea, but I suspect that there will be other members who, like me having spent a long time trying to adjust their carbs and then found that the tail pipe is still an even black, have decided that it is an impractical exercise with the usual XPAG and SUs. Well, Bjarne has been running his TC with a catalyst for 2 years! He has of course, been using Unleaded fuel but without additives or a modified head! (Bjarne's letter arrived the week after I had taken my cylinder head to have insets fitted!) I had come to the conclusion that this was the best way of dealing with the approaching problem despite the fact that David Locke from Broquet keeps sending me anecdotal evidence that the fitting of his product is a much cheaper solution. I have also received via Harry, advertising information on another 'fuel catalyst' product which makes similar claims about improved combustion and economy. It appears to be cheaper that its rival and details can be obtained form EcoTIN (01579 344751).

You may remember that many months ago I floated the idea of a comprehensive index of M.G. technical articles to supplement the annual Bulletin index produced by Bob Snowden. I know that Bob intends to produce a combined index from recent Bulletins but the idea of the comprehensive index was to include reference to articles appearing in other magazines which are readily available to M.G. enthusiasts. Despite some initial preparatory work by Lyn Harcombe the idea has not progressed very far, largely due to lack of time and lethargy on my part. In the meantime however, Keith Maywhort and Ernie Evans have been beavering away producing their own indexes of Bulletin articles on computer and Colin Mulford, Roger Clements and Jonathan Taylor have volunteered to help in the magazine search. The calling of the EGM allowed Ernie, Keith, Jonathan and I to get together over a snack and a drink to decide how best to proceed. We made significant progress in a short time and I am pleased to be able to tell you that Ernie has agreed to act as co-ordinator for the project. If there are any further offers of help Ernie can be contacted at: Llwyn Uchaf, Derwen, Corwen, Denbighshire. LL21 9SH (Tel/Fax 01824 750677).

Questions

  • Having yet again bled the brakes I wonder if anyone has had experience of, or can advise on, converting a TF to rod or cable operated brakes. A triple M owner tells me that they are much easier to maintain and provide very good braking without all the hassle of hydraulics.
    A Buffone, Bath.

  • The wire on the fuel gauge tank sender unit of my TC is loose. Is this correct? The number on the engine block is 24142. According to Sherrell it should be 24146. Any explanations? Under the front wing there are two holes for the bolts which hold on the side lamp. To which one should the wing stay be attached? What is the resistance of the ignition warning lamp?
    Keith Maywhort, Nottingham.

  • My speedo cable leaks oil in a really big way but its better to leak then pump it into the speedo head. Does anyone know how to route the speedo cable so that it is not so near to the ground. I keep expecting it to catch on something.
    Paul Edwards, Newbury.

    Answers

  • Does anyone have experience of using Colourtune plugs as an aid to turning the likes of the XPAG engine? Do they have any merit? Should they be used as per instructions, or would other conditions produce the best results? Out of interest, what overall MPG do people usually get from their TCs? (I'm only getting around 20mpg at the moment, it has been nearer 30mpg in the past.) (No332)

    I must confess that I have for years tried to become friends with my Colourtune, with no success at all. But as tuning TC caburettors the S.U. way gives no problems (well, you have to do it properly, and if I do, the result will be about 32 mpg.), I have given up "Colourtuning" for good.
    Bjarne Bergengren, Helsingborg, Sweden.

  • The collets on my windscreen wipers are tightened as far as they will go, but the wipers still slip on the spindles. Is there any (reversible!) way to get them to grip better? (No 332)

    For your wipers, have you tried wrapping some very thin plate brass (0.1 - 0.2 mm) around the spindle?
    Bjarne Bergengren, Helsingborg, Sweden.

  • 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? (No330)

    First ensure that the inside of the float chamber is connected to the atmosphere. This is done by using an internally notched fibre washer to secure the top. Using a plain washer will result in pressurisation (by fuel vapour) of the float chamber leading to excessive flooding. Assuming that the float chamber is connected to the atmosphere the probable cause of poor hot starting is an overheated carburettor. This can be cured by inserting an insulating block between the inlet manifold and the carburettor; use stainless steel screws if you can as they are poorer heat conductors than mild steel. If you cannot obtain insulating blocks of the correct pattern they can be made from nylon 66 sheet which is obtainable from Radiospares (RS). A heat shield may also be used to prevent radiating heat from heating the float chamber, although I have found this much less effective than an insulating block which I consider essential. An added bonus is that you will find the carburettors much easier to tune; you will also achieve much lower CO levels. My TC reaches the emission standards of the last cars built without catalytic converters even though it has the same set of pistons that it had when I brought the car in 1971!
    Richard Brown, Heathfield, East Sussex.

  • Both carb bodies have damaged threads where the banjo fixes the fuel bowl to the bodies. One has had a bush insert which is slightly loose, the other tapped to 1/2" Whit and a crude banjo made up to suit. Both wobble somewhat and leak slightly, so I'm trying to engineer better solutions, maybe an interference fit bush loctited and/or doweled in place in the alloy bodies. Does anyone have a proven and simple repair suggestion? (No331)

    The thread for the banjo bolt could of course be repaired, if you know what you are doing, with a 5/8"-7/16" BSF bush, (don't forget to clear the fuel channel), but to repair the rear, old type alloy flanges would be more difficult. The brass washer and the second fibre washer, by the way are there to prevent the bold head from mashing a single fibre gasket.
    Bjarne Bergengren, Helsingborg, Sweden.

    I have repaired the threads on many carburettors using helicoils.
    Tony Brier; Ellerton, York.

    TF Emissions

  • Could any member please advise as to the best means of minimising the amount of Carbon Monoxide emitted from my 1954 TF 1250? I am not personally aware of this being a serious problem but my beloved, who is slightly asthmatic, swears that unless I solve the problem, she is not willing to go out in it again with the hood down. As a very last resort I could put up the hood but that defeats the whole point of enjoying open air motoring!

    The carbs have recently been overhauled with new jets, needles (standard), seals etc. The present level is around 6% CO on tickover which I am told is pretty good for an old timer. There do not appear to be any leaks in the exhaust and I wondered whether re-routing the exhaust to the driver's side or using a weaker needle may be options. It would be interesting to learn from other members what their CO emission levels are. (No332)

    I agree, 6% CO is intended normal for an XPAG, tuned after the S.U. book. If you take care , you could come down to 4,5%, but any lower, and the tickover will be impaired. If your partner happens to be one of those endearing women, who have twinkling eyes, and thus there is no question of exchanging her, your solution is a catalytic converter. Yes, I mean it! The whole thing started as a joke, of course. Why not try to keep the environment freaks happy?

    So I put a cat on my TC, and Bingo!, the tickover CO was down to 0%. Well, not all that simple, you have to have your carbs really on their toes, and the adjustment is a question of one 12th of a turn up or down on the jet adjusting nut, but I have run the car like this for a couple of years, and it runs beautifully, the figure for unburned fuel is only slightly higher than that of a modern cat car. Leadfree fuel, of course, but I haven't converted the cylinder head to leadfree, I run the car about 5-6000 miles a year, with no problems as yet.

    I picked up a used Golf cat from my friends at the junkyard and adapted it to the front exhaust tube about where the clutch hosing tapers off to the gearbox, the Golf cat having inlet and outlet off centre, so it can easily be turned into the most favourable position. (The flange and gasket, by the way, is the same as the TC one below the manifold, so it will look the part, and you can make it exchangeable if you want to.)

    There could be some trouble due to the TFs bigger carbs, (I think they were put there just to impress the Americans), but I think they will only alter the figures slightly. you must be prepared, however, to retune the carburettors as the jets and needles are worn down by the fuel. Good Luck! And give my best to the Young Lady!
    Bjarne Bergengren, Helsingborg, Sweden.

    I have reduced the levels on my TC to less than 2.5% by using insulators between the carburettors and the inlet manifold, running with the ignition set to 8o BTDC and electronic ignition. The latter was fitted to eliminate the requirement for periodic (and frequent) adjustment and is not essential. The engine has a 9.3:1 compression ratio. I was using Champion L86C plugs or near equivalents and have recently found some much more suitable Bosch plugs (W5AC) which should allow me to reduce the CO level further. Using a weaker needle will not help as the problem is caused by the float chamber being too hot.
    Richard Brown, Heathfield, East Sussex.

    Carbon Monoxide is only one of the by-products of the combustion process and is itself odourless, as many a poor soul has found out to his cost. Seeking to reduce the CO level from an already admirable figure is therefore not going to help Mrs Waite's problem. What is needed is to make sure that the fumes are ejected sufficiently clear of the rear of the car not to be sucked forward by the back-draft. Russell could check that the exhaust pipe projects at least two inches beyond the rear bumper and perhaps consider fitting an exhaust trim, such as those supplied by The Classic Collection, 143 Cannon Hill Lane, Raynes Park, SW20 9BZ (Tel. 0181 5430551). These chrome trims are either straight, to lengthen the exhaust pipe, or a shrouded fan shape to deflect the gases downwards. Failing that, I believe that gas masks are still available......
    Jake Wilson, Paignton, Devon.

    Carburettor Flange Distortion (TC XPAG)

  • The alloy carb flanges that mate with the inlet manifold are again bowed, even though I flattened them by sweatily emery papering against glass about a year ago. The bowing causes a slight air leak at the manifolds which results in erratic idling. If I flatten the flanges again, presumably the same thing will reoccur - until I've ground the flanges to nothing! Presumably it's the differential expansion between the cast inlet manifold and the alloy flanges, tightened up but only separated by a thin gasket, that causes this when everything gets to 80 degrees. Sherrel mentions this nasty alloy, but I'm not about to pay out hundreds of quid for replacement carbs! Has anyone experienced this or got ideas for a suitable fix? I did think of putting in a thicker gasket such as the MGB/midget plastic spacer that has been advocated to help with fuel vaporisation problems, but for some reason the alloy air intake already almost touches the inside of the bonnet, so any thicker gasket/spacer will push it out even further, so doesn't seem practicable. (No332)

    I would in the first place recommend a couple of new or undamaged carburettor bodies. Used original TC ones are getting harder to find, but there are a couple of similar ones, perhaps more easily found, that you can use, with or without alteration. To repair the rear, old type alloy, flanges would be difficult.
    Bjarne Bergengren, Helsingborg, Sweden.

    When, in the sixties, I was running my TC as my first and only car I also fought a losing battle with the leak from the float chamber fixing banjo. It seems to me that the braided petrol pipes are always conspiring to move the float chambers and loosen off the connections, Eventually I stripped the thread in one body and drilled a bolt (7/16 BSF?) to act as a longer banjo bolt and reach the threads the standard bolt couldn't. At the same time I ground off the shoulder of the other banjo bolt and used the top-hat shaped neoprene washers used on the MGA. That solved the problem. In the mid-eighties when I was getting the TC back together I took the dreadful old bodies complete with distorted flanges and worn-out bushes to a well known SU supplier. They told me that the only answer was new bodies and that they cost about 57 a pair complete with new spindles and butterflies. I'm sure that it was money well spent because the butterflies close properly and I was able to get the idling speed down to a sensible level and the flanges did not leak so I could set the mixture. I again used neoprene washers. Before we get into the originality discussion my rule of thumb is that if I could have done it when I first had the car then it's OK. Anyway, you cannot really see the neoprene washers. So, my answers to Les are:

    a. it is worth getting bodies onto which the rest of the carbs can be assembled.
    b. a collection of washers was used because neoprene hadn't been invented.

    I have telephoned the SU suppliers and they are a bit cagey about supplying bodies; they might need talking to about that, but the neoprene grommets (AUC 1530) are 1.04 a pair and the holding-up bolts to go with then (eg AUC 1335) are available in various lengths at 4 to 5 a bolt - and well worth it.

    If I could be contentious on the more general subject of time and money: even though these cars are a hobby our time is still worth something. Is it really sensible to waste it on grinding those dreadful old bodies when we know they will distort again - more quickly because they are thinner? Then we have to fiddle about fixing those stripped threads and presumably rebushing the spindle bosses. Why not fork out and fix the problems for good?
    Paul Edwards, Newbury.

  • Some time ago I brought from Octagon a replacement oil filter element (TJFP3312) to fit the existing vertical conversion with removable filter. The previous element was a zig-zag paper concertina type with thin wire spiral wrapped round to retain shape. The replacement is different, having a paper band with holes in around the element, but presumably under this covering is a similar concertina construction. Although the element fits the canister as the length and metal ends are the same diameter as the original, the diameter over the paper is larger than the original, thus reducing the space between canister wall and element, presumably making it harder for the oil to squeeze past, to use the technical parlance. "So what?", you might all groan! Well, this results in 5 psi lower oil pressure (giving 40 psi running), which is a cause of slight concern. I even put the old element back in to prove the point before someone asks!. Any comments? (No332)

    Talking of oil filters, You must of course use one that lets through enough oil, but having said that, the trick is to use a modern oil of premium quality, marked, say, 15W-50, and no nostalgic nonsense with "Classic" oil, like shoe polish when cold and like water when hot. If this does not help, check the steel ball of the bypass valve for roundness, and put in a new one if necessary. As a last resort stretching the bypass spring a little, might help.
    Bjarne Bergengren, Helsingborg, Sweden.

    Distributor Types - TC

  • The distributor fitted to this late TC with standard XPAG is type 40162. I believe the correct sort should be 40048, but there doesn't appear to be much difference from the various curves I have seen published - unless anyone advises otherwise! However I do have a spare distributor part number 40058A, which has a shorter stem than 40162. It seems that it would fit perfectly if the micrometer adjustment is omitted, because this normally clamps on the stem just above where it protrudes from the engine block. So my surmise is that 40058 is identical to 40048 except for the stem; can anyone confirm this or advise what engine 40058 comes from?

    If I rebush any of these distributors with an off the shelf bush from one of the T type suppliers, will it need reaming or is it a push in and ready to use item? This obviously requires removal of the pinion, so is the retaining pin reusable or does one fit a new one, and should it be peened over? (No332)

    The distributors you mention are all virtually the same. The 40048 was used for the TC 1946-49, the 40162 for the TD 1950-52 and the 40058A for the Morris 10, 1937-47, the only difference being another set of springs in the latter one giving it a curve that's a little less hot. There could also be some difference in the adjustment mechanism, which would account for the difference in length.
    Bjarne Bergengren, Helsingborg, Sweden.

    Distributor 40048 was fitted to the TC. Distributor 40058 was fitted to the 1953 M.G. 1.25 litre saloon and the '38 to '48 Morris 10. Distributor 40162 was fitted to the early TD. The only difference between 40048 and 40058 was that the former was fitted with a micro adjuster which necessitated a different clamping plate 405903 against 404422. Also the weight of spring set was different. 40598 against 405583 which gave rise to different ECM curve, NO 279 against No 267. Both had a range of 14 to 16 degrees. 40162 was closer to 40048, having the same spring set and ECM curve. The only difference being the microadjuster. 40162 uses the same clamping plate 40422 as the 40048 distributor.
    Don Spurr, Portishead, Bristol.

    Further to Neil Cairns interesting article on engine threads, in the September Bulletin, are taps and dies available which correspond to the French metric threads in the XPAG? (No 333)

    The only size that is different from the standard ISO metric threads is the 8mm x 1.0. This is available from several suppliers as "Metric Fine". Namric, Hove, 01273 779864, Taps - 7.50, Dies - 10,00 The Tap and Die Co., 0181 888 1865 Any branch of Buck and Hickman (But at astronomical prices). The other sizes, 6mm x 1.0 and 10mm x 1.5 are best brought from a local tool supplier as they will be cheaper there. Incidentally I have a thread insert kit form the 8mm x 1.0 thread which I would be willing to lend to any member as long as they paid for their own inserts.
    Bev Archer, Neath, West Glamorgan.

    Roger Furneaux of "Mad Metrics" (01932 243534) stocks everything to do with such threads.
    Neil Cairns, Leighton Buzzard, Beds.

    Tips and Comments

    TD cams
    In Bulletin No329 p19 Allen Howell stated that he fitted a standard cam AAA3309 to his 1953TD. According to my records the early TD was fitted with an AAA5776 cam and the late TD with an AAA3096 cam.
    Don Spurr, Portishead, Bristol.

    Old tyres
    I must disagree with Dave Whitfield's over cautious answer (No325) to the question in No323 about tyres which have stood for some years. Of course you will never be wrong if you decide not to risk old tyres by buying new ones, but this denies the experience of myself and, I believe, others who find these old tyres to be as tough as old boots. The sidewalls are so strong that they will almost stand up without any air pressure. Personally I am still using two tyres which I put on my TC in the 1970s. In spite of not always being kept on blocks (or even properly inflated) for around 15 years "awaiting restoration" they are still going strong without any flat spots. So I suppose my answer must be that it depends on how good the tyres are. Trust your knowledge and experience. Inspect them carefully and, if all is well, fit them and keep an eye on them and if there are no problems - carry on.
    Ian Thomson, Newark, Notts.

    Overrun Backfiring
    I had "popping" in the exhaust of my YB on overrun which was actually quite a nice sound - very period. It turned out to be caused by a hole in the silencer which was too small to see or hear. Apparently air is drawn in and ignites the unburned fuel.
    Ian Thomson, Newark, Notts.

    Stage 2 misfiring
    If anyone is having ignition problems with a Stage 2 XPAG (CR 9.3:1) they could try some Bosch W5AC plugs which have completely cured a long standing mis-fire which usually occurred when accelerating with a hot engine.
    Richard Brown, Heathfield, East Sussex.

    Unusual tools
    I'd be interested to know what unusual tool (ie. not screwdrivers, spanners, pliers) members have found very useful in the garage. For me it is 'bend-a-light' - the torch which has along thin stem ending in a tiny, high powered bulb. This tool has allowed me to see into the most unlikely places in ways in which the ordinary torch could never manage. Checking battery fluid levels (especially in the J2 when an acrobatic training is required), checking the presence of oil seals in half shafts, examining the inside of the petrol tank and checking threads on tapped holes such as cylinder bolt holds in the block, are all examples of recent use of my bend-a-light. Round the corner behind the water jacket plates to discover piles of sludge and rust flakes and also the dash wiring connections have been brought into view by this useful tool.
    There must be other tools which Octagon members have found useful. So how about sharing your experience with the rest of us?
    Bob Snowden, Exeter, Devon.

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