Lotus Elan

hot cylinder after rebuild of twin cam motor

PostPost by: Rich » Fri May 17, 2019 3:28 am

I recently rebuilt my twin cam motor and now number 4 cylinder is 200 degree hotter than the other 3 which measure 300 degrees at the exhaust manifold after running the motor in an engine stand for 5 to 10 minutes. I have an after market 4 into 2 into 1 ceramic metalic coated headers so its easy to read each exhaust tempature. I switched the front carb with the rear and number 4 is still hotter than the others. I can't find any air leaks in the intake and all the jetting across the carbs is the same. The timing is right on and the leak down and compression in number 4 is the second best of all the cylinders. Any suggestion as to a solution will be appreciated.
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PostPost by: nmauduit » Fri May 17, 2019 7:44 am

is it a Stromberg head ? if so at what rpm did you have the engine run before measuring the header temperature ? I suspect that at idle the flow could be easier to imbalance (inlet differences, ) than at say 3000 or 3500...
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PostPost by: Grizzly » Fri May 17, 2019 12:25 pm

How well does the vacuum balance up across the carbs? I had issues with my rear carb too that turned out to be a mixture of the Inlet manifold flange being slightly warped, new o-rings being too hard and a leaky servo (+2). One of my symptoms was much higher temps on the no four branch of the exhaust manifold on progression also a very lean colour to the plug.

I think i may also have had a bad valve guide too as they were replaced at the same time (it was a bit smoky on cold start up) but just like you i did a compression test, Leakage test etc and all appeared well.
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PostPost by: Donels » Fri May 17, 2019 1:56 pm

Maybe there is some blockage in that exhaust pipe causing a higher back pressure?
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PostPost by: mbell » Fri May 17, 2019 11:24 pm

Have you checked valve clearances since fastening the head down?
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PostPost by: Chrispy » Fri May 17, 2019 11:32 pm

Hows your valve clearances?
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