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Old 01-28-2015, 03:45 PM
J-Mech J-Mech is offline
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Join Date: Apr 2013
Location: Oblong, Illinois
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My book shows .007-.010, so not sure where you got those numbers. They're close, so NBD, but it always amazes me when you find differences.

If the piston manufacturer lists a spec with the piston (instructions in the box) then go with it. Otherwise, the book spec is correct. It's an air cooled engine, so they run a wider clearance spec than a water cooled engine because of expansion. I'm not sure how many air cooled engines your machinist has bored, but if he knows anything he should know that that is normal. As far as what works and how do you know if it's ok even if it's out of spec..... well, if the machine shop goofs, then it's their job to correct it. If it's too tight, then they didn't finish their job. If it's too loose, they goofed the finish. I like to see numbers in the middle of the range with exceptions made on special builds. If you find that a bore is too loose.... well that's your call. They'll run, just not as long of life as it starts out basically "wore".
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