Technical


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Extract from January's Octagon Car Club Bulletin

QA Technical Torque


In last month's column there was an article by Phil Marino on T-type stub axles during which he advised ensuring that the car is on the ground before using the wheel hammer. This conflicts with the advice given by Rudge Whitworth in the cards referred to by John Young in Tips and Comments. Perhaps the manufacturers were not expecting their wheels to be in use on axles which were over 50 years old. My money is on Phil, provided that the nuts have been hand-tightened whilst jacked-up, but the cards are well worth a close inspection. Unfortunately they are not in perfect condition having slipped down between the ash frame and a metal sheet in the door sometimes before 1941 when the car was laid up and having remained there until 1996. They are vintage in origin probably referring to beaded edge wheels rather than the later type fitted to most M.Gs. Nevertheless, the principles remain valid and it is interesting to read of the lengths to which owners would go to compensate for wear before 'planned obsolescence' became a feature of our society. John is not a club member but kindly sent the material at the suggestion of Bruce Brown.

If anyone has any further information on these wheels please let me know and I will pass it to John who expresses an interest in more information.

Editor's Note: I am afraid that the photocopy of the cards sent by John Young was not of the required clarity for reproduction in 'The Bulletin'. However, Malcolm has copied the text of the wheel changing card.

Questions

  • Does anyone have experience of using Colourtune plugs as an aid to tuning 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 30 mpg in the past.)
    Dave Norris, Aberdeen.

    Slack Wipers

  • 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?
    Dave Norris, Aberdeen.

    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.
    Russell Waite, Ulverston, Cumbria.

    Carburettor Fuel Bowl Fixing Repair (TC XPAG)

  • 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 getting 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? Can someone confirm that the original banjos are 7/16" BSF (that is what the bush is tapped to)? Carburettor and spares supplier literature show the banjo bolt having three washers below the bowl, comprising a thin brass one between two fibres ones; why, as opposed to just a single fibre one?
    Les Meer, Worcester.

    Carburettor Flange Distortion (TC XPAG)

  • The alloy car 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 idle speed running. 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 alloys 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 replacements carbs! Has anyone experienced this or got ideas for a suitable fix? I did think of putting in 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.
    Les Meer, Worcester.

    Cylinder Head Pushrod Tube Oil Leaks (XPAG)

  • Oil slowly collects on the head in the recesses around the spark plugs. I believe, following careful wiping, that it is from where the pushrod tubes enter the upper part of the head, rather than from the more expected sources of rocker cover gasket leak or cooling fan blowing on oil droplets from other leaks. Has anybody experienced this?
    Les Meer, Worcester.

    Speedo Drive Oil Leak TC

  • Gearbox oil drips from the speedo cable at the bottom of its "dip" under the gearbox (no it's not engine oil from the crankshaft rear seal!). Presumably the bush/scroll in the speedo drive in the gearbox is worn, although I gave it a good clean-up when overhauling the gearbox. Is this a common fault and is there a cure?
    Les Meer, Worcester.

    Oil Filter Construction Causes Reduction of Oil Pressure (XPAG)

  • Some time ago I brought from Octagon a replacement oil filter element (TJ FP3312) 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 cannister 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 cannister 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?
    Les Meer, Worcester.

    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 from 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 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?
    Les Meer, Worcester.

    Answers

  • 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? (330)
    The standard TC 7 1/4" Job is next to useless with anything over a mildly tuned engine. One used to be able to buy a competition version of this in the 1960's but now?

    I have not used these for years, preferring the 8" TD2/TF flywheel and clutch, with the added benefit of small, solenoid operated starter motor. The standard TF clutch works perfectly well for a long time with power outputs up to about 75bhp at the flywheel, and an MGA twim cam one ought to cope with well over 110bhp, for obvious reasons! The MGA clutches are interchangeable on TF flywheels.
    It has been well repeated previously over the years that a TC bellhousing needs relieving a bit to allow proper operation. My road going TB, with something between 75 & 80bhp works perfectly happily with a TF clutch. We T-racers use a 7 1/2" Ford Escort (Mk 1&2) diaphragm clutch, on specially lightened flywheels, but that is another story!
    Paddy Willmer, Potton, Sandy, Beds.

    Tips and Comments

    Rudge - Whitworth Detachable Wire Wheels
    I recall discussions some time ago about the correct manner of fitting these wheels. There were those who argued it was not necessary to hammer the wheel nuts tight and those who declared the wheels would not stay put if the bearings were greased or oiled.
    When I brought my 18/55 Talbot I took out the leather upholstery on the doors. The bottom half of these doors is strenghtened with sheet metal. On removing this metal I was delighted to find three pieces of card.
    The first two items were cards produced by Rudge-Whitworth describing exactly how to fit their wheels. In addition, reference is made to the need to oil the mating surfaces of the hubs and the wheel nuts. The biggest surprise was a chart specifying the tools necessary to assess wear. I have never seen the plugs and rings described in this section either in motoring literature or at autojumbles. Clearly there is more to a decent set of hubs, nuts and wheels than meets the eye.

    The last card was a lovely social document recording the fact that my 18/55. FR7295, had been parked in Orchard Street, Westminster at 4.30pm on 10.5.32 and must leave the parking space by 6.35pm; the penalty being 5 for a first offence and 10 for a second or subsequent offence. 5 seems an a enormous amount of money for the time, equivalent to a skilled man's weekly wage, testifying to the fact that London has always been crowded, if the penalty for adding to the congestion is anything to go by.
    (I have copied the text of the wheel changing card. I hope that it will be possible for the printer to copy the others. - MT) It wasn't! - Ed.

    "To Change a Wheel - Undo the locknut by tuning it in the direction in which the wheel revolves when the car goes forwards.
    Pull off the wheel, see that the inside of the spare wheel hub and the outside of the permanent hub are clean and well oiled; push the wheel right home on the inner hub, fill the groove in the lock nut with oil and screw up the lock nut, hammering it tight while the car is jacked up.
    It is often found after a change of wheel and a run of 20 or 30 miles a slackness has developed between the nut, wheel and hub, either by the bedding down of the parts or by the grinding away of some dirt that has got there by accident. (This slackness is something wrongly attributed to the locknut unscrewing, a thing which never happens). Therefore after a run of 20 or 30 miles the wheel should be checked for slackness by rocking, that is to say, pushing backwards and forwards on the tyre, and should there be any movement between the nut and the hub the lock nut should be tightened up with a hammer while the car is jacked up. Slackness seldom develops after this second tightening, but it is desirable from the time to examine for slackness by rocking the wheels. The spare wheel should always be carried on a dummy hub, or fitted with a dirt excluder.'

    John Young, Harrogate, North Yorks.

    30 M.P.H. Warning Lamp

    The question posed by Mr. Gordon Royal for an explanation of the operation of the 30 m.p.h. warning lamp ('thirtilite') raises a companion list of other applications for this switch mechanism. The electric switch in the TC speedometer that turns on the 'thirtilite' is a rotary switch that closes at a particular pointer position. This switch consists of a long finger that contacts a silver plated (?) radial arm attached to the deadband (stabilizator) wheel. The silver plated arm is adjustable and rest against an insulating disc of what appears to be a paper reinforced phenolic resin. Since this arm can be rotated to any angle, the switch can be adjusted to close at any desired pointer position (m.p.h.).

    If you want a 65 m.p.h. warning lamp rather than a 30 m.p.h. warning lamp, simply rotate the arm. To rest the arm hold the dead band wheel still with one finger and then rotate the arm to its new position by pushing it with a small screwdriver. In fact, there is no impediment to transferring the switch mechanism from the speedometer to the tachometer and thus employing it as an engine r.p.m. warning lamp. Set it to any r.p.m. you choose. These switches, which were included in the later speedometers, can be reset or transferred to activate lights, whistles and bells that comes on at any road speed or engine r.p.m.

    Purchase a few of these wonderful old chronometric mechanisms with their warning switches and you will have enough parts to do anything you want. Interchange end plates, the dead band wheel, the transfer (recorder) wheel, the switch bits and you will have constructed the Jaeger Tachometer that before existed. Chronometric mechanisms are symphonies of mechanical parts that incorporate many wonderful mechanical subtleties. They are beautifully made, have interchangeable parts, and with proper tooling are a joy to work on.
    Carl N Cederstrand, Brea, California.cederstrand@earthlink.net

    I hope you have enjoyed the first edition for 1998. Please keep writing to me Malcolm Taylor, Whisket Green, 56 Daisy Lea Lane, Huddersfield, HD3 3LL.

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