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Hi folks

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Hi folks

Post  meditek on Tue Dec 15, 2009 4:43 pm

Hi,

I signed up here to try and get an answer to something that has been puzzling me for 40 years!

Back in 1968 I bought a +2 kit. When it worked the car was fantastic. Unfortunately the engine wasn't. It blew valves every 600-700 miles. I admit to driving it hard but it did have a rev limiter! The local dealer replaced the valves twice. I even had to have them done at at Italian garage when down in Italy. Finally, I went down to the Lotus factory who did something and handed me back the car with the carbs so out of balance that the engine ran like a nail. The valves blew again after 500 miles. I finally sold the car to Rob Walker's at a 200 profit!

My question is whether valve problems were a feature of the twin cam engine and, if so, was the cause eventually found? At the time everyone involved appeared not to have a clue.

I recently drove a race prepared Elise at a supercar day. It didn't feel like a car that Chapman would have designed.

Thanks

meditek

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Re: Hi folks

Post  GrumpyBodger on Tue Dec 15, 2009 8:49 pm

Hi Meditek,

Well you certainly had some bad luck with that Twincam.
I assume that it was always an exhaust valve that "burned out"?
Twincams are renowned for burning quite bit of Oil.
One reason for this is due to the lack of Valve Stem Seals.
However the Oil leakage via the Valve guides would need to be high to cause the problem your Engine had.
Generally speaking burned out Exhaust valves are mostly caused by Oil entering the Combustion chamber via the intake Manifold, that Oil being introduced due to a fault in the Crankcase ventilation system, which int the case of the Twincam breathes into the Carburettor Air Box.
A film or more than that of Oil in the intake tract would be a good indication that this was the problem.
There is also a possibility that a lean mixture could have caused the problem but I would have expected Spark Plug problems to occur before a Valve burned out.

All of this written from a distance & a load of assumption.
At the time an experienced Motor Mechanic should have been able to diagnose & cure the problem.

Cheers
John
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Re: Hi folks

Post  TimS on Wed Dec 16, 2009 3:03 pm

Good reply John, I knew I should keep quiet as you would do a much better sufficient reply than I ever could.
Great to see your knowledge and wealth of experience used.
Cheers,
Tim.
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Re: Hi folks

Post  GrumpyBodger on Wed Dec 16, 2009 8:22 pm

Thanks Tim,

I'm still nervously awaiting someone pointing out the errors in my hypothesis

Cheers
John
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Re:

Post  Trigger on Wed Dec 16, 2009 8:35 pm

GrumpyBodger wrote:Thanks Tim,
I'm still nervously awaiting someone pointing out the errors in my hypothesis
Cheers
John
Well rest assured it won't be Tim or myself Razz

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Re: Hi folks

Post  meditek on Thu Dec 17, 2009 5:08 am

Thanks for the info grumpy. The engine was new and the exhaust valves burned out the seats. Mixture was fine as far as I remember. Hardly used any oil either. Had the guys up at Yarm baffled and presumably baffled the factory too. I suppose that it will forever remain a mystery.

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Re: Hi folks

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