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914World.com _ The Paddock _ Race engine piston to cyclinder clearance

Posted by: Driver174 Jun 17 2018, 11:07 AM

914-4 2.0L approx. 10.5:1, JE forged 2618 Aluminum pistons, Web 163/86b cam

JE clearance guidlines say to set clearance to .0035" along with a note "some applications may require more clearance".

I had cyclinders bored 0.75 mm oversize with piston clearance of 0.0035", but am having second thoughts; maybe should of increased clearance to .0045.

Engine will see road racing conditions, so will get run hard for 20-30 minutes or more during each race. Should I increase the piston clearance? I'm assembling the engine now so it's not too late to address.

Thanks,
Jim

Posted by: Driver174 Jun 19 2018, 12:19 PM

Any thoughts before I assemble this engine? I checked the clearance of each piston/bore, and am going to put largest of .0038” in # 3 position.

Thanks again,

Posted by: Racer Chris Jun 20 2018, 06:39 AM

Probably not too many engine builders looking in this forum on a regular basis, Jim.
I bet you would get some opinions if you posted the same topic in the Garage.

Posted by: wndsrfr Jun 20 2018, 07:57 AM

Len Hoffman...(HAM inc.)...advised me when I put JE's in my 2316....I advise you to PM him before you increase that clearance.....as I recall he said not to exceed .0025", so you're maybe past that already....

Posted by: Krieger Jun 20 2018, 11:23 PM

FWIW, I just finished building a 911 six. I used Wayne Dempsey's engine build book a he recommends 1.5mm clearance for intake and 2.0mm for exhaust.