Lotus Elan and Lotus Elan Plus 2 Forums

My workshop manual quotes two exhaust valve clearances for the exhaust side, before and after engine 9951. Trouble is, I can't find the engine number to relate this to. It's a 1970 S4. Does anyone have any clues?

Regards

Peter Burgess

I have always assumed the difference was due a change in the exhaust valve material affecting its thermal expansion. What your current exhaust valves are made of are anyones guess and thus what clearance to use is hard to estimated. I have always used the later clearances setting the exhaust at 10 thou, assuming Lotus change to a similar stainless material as I currently use with its higher coefficient of thermal expansion in 1970.

Valve clearances are not so critical from a performance perspective on the exhaust side and larger is safer as well so erring on side the larger clearances of the later engines cannot really hurt also.


Rohan

The engine number on my 1969 S4 is G20099: roughly twice the break-point between the two valve clearance specifications. A quick look at Jim Boone's registry shows similar engine numbers for other S4s. You can safely assume that you should use the later specification on your 1970 S4.

Rich Boyd