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Re: valve clearance problems (help) (archive)

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Posted by WH on July 11, 2000 at 19:52:30:

In Reply to: Re: valve clearance problems (help) posted by Bill R on June 29, 2000 at 08:07:03:

: : CAN ANYBODY TELL ME WHAT WOULD BE A SAFE (PISTON TOO VALVE) CLEARANCE, ON MY 3.0E3. I HAVE PLACED A 3.5L CRANK IN THE ENGINE WHICH HAS A STROKE OF 86MM AND ADDED A HIGH LIFT ALPINA SPEC CAM. THE STANDARD PIANO TOP PISTONS HAD TOO BE MACHINED FLAT. INLET VALVE IS MISSING TOP OF PISTON BY QUITE A LOT, BUT THE EXHAUST VALVES ARE WHAT I AM CONCERNED ABOUT.

: I think the original spec is .012". Korman's recommendation for my modified 3.0 (9.5 compression, 300 degree regrind cam) was .010 - .012". Hope this is of some help and good luck! Bill

If I'm not mistaken Warren was asking for the piston to valve clearance NOT the rocker to valve clearance, right?

.012 is fine for rocker/valve clearance (.010-.012 is stock for most older BMW's).

As for building an engine with piston to valve clearance of only .012"--I wouldn't, when you rev that engine to 6,000+ rpm I'd bet you make contact. A safer margin would be at least .060-.085 thousands. Put some clay on the pistons do a dry assemble w/correct head gasket and cam timing with the head torqued down. Rotate the engine a couple revolutions --pull the head, measure the thickness of the clay between where the valve contacts and the piston. That will be your piston to valve clearance.

WH


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