Interesting point, Bill. I reached the same conclusion about ten years ago when
researching my twin cam. Also was able to confirm by talking to some guys who
raced'em when new. I found one who reported having solved the problem by using
a
float bowl arrngement different from stock. Said the car was so rare he was
never
caught by the tech guys. And as a result we have a bunch of neutered twinkies
with 8 to 1 compression. John
WSpohn4@aol.com wrote:
> Thanks for the Twinkie stuff, Neil.
>
> One comment - the reason that Twincams burned pistons was not apparent to it's
> contemporaries, and the material quoted by you appears to be older factory
> stuff.
>
> The real reason that the Twincam engine had warranty problems was an
> undiagnosed fuel frothing problem that leaned the engine out and caused the
> piston burning problem for which it became notorious. This condition occurred
> at two specific engine resonant frequencies that coincided with (I am going
> from memory here as I am too lazy to dig out my files) around 2500 and 5500
> rpm. The earlier one would normally be passed pretty quickly, but it was in
> the cards for the engine to be held for some time at the latter rpm on the
> highway and duriing competition. Apparently the vibration had a tendency to
> jam the fuel float on the centre pin resulting in starvation at those rpm.
>
> Obviously it wouldn't happen every time and would have been infuriatingly
> difficult to diagnose. One of the first tips that made the lights go on for
> the brighter lights that were trying to figure this out was that ALL of the
> cars that had problems had SU carbs, and NONE of the competition Weber
> carburetted cars had these problems, often despite more rigorous use.
>
> The solution is easy - use Webers, or have your original manifold grooved for
> 'O' rings. If you don't want to bother with the machine work necassary for
> this, you can use the special Weber gaskets that are essentially an O ring
> attached to a carb gasket. As it happens, the ones from a 45 DCOE also fit the
> H6 SU bolt pattern when turned diagonally. You also need double wound
> 'Lawrence' washers as if you just reef the nuts tight it is as bad as having
> no rubber in the setup - they need to be able to flex.
>
> Have a look at Lotus or Alfa engines for similar applications. Too bad they
> didn't figure it out sooner!
>
> By the way, a Twincam in good tune will make the sub 10 second 0-60 time - the
> others given to the magazines were off colour and for some reason badly tuned
> and prepared. Hope they fired the guy responsible.
>
> Having said all that, you are quite right that the engines rev so easily that
> many were broken simply by indiscriminate use of a heavy right foot. It is
> basically a totally different creature than a pushrod engine, and for anyone
> that experiences one it is hard to go back!
> What they clearly should have done in retrospect was to fit a rev limiting
> rotor, as Lotus did in the Lotus Cortina (these will in fact work in the
> Twincam and are calibrated for 6500 rpm). I don't know if these were available
> in 58 but it would have prevented half of the warranty claims, and proper de-
> bugging before production might have solved the fule problem.
>
> Ironically, the problem never showed on the test bed as they used a different
> fuel system than stock. If they had detected it early enough, I would be
> willing to bet that we would have had 120 bhp Twincams in 1800 size for the
> Bs, at least as an option. Sad, no?
>
> Bill S.
> (Real MGs have 2 Cams!)
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