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XL-erate

Cylinder honing & piston clearance?

8 posts in this topic

I'm honing out a cylinder on an ATC 110 horizontal engine, same-same as a CT90, Trail 90. What's a safe piston/cylinder clearance for utility use, not racing or that sort of thing? Piston is 53mm so what diameter bore do I want to see? Thanks!

XL-erate

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No specific knowledge of that engine, but the normal rule is .001 for each inch of bore. Using that would say .002, and a max around .003. I'm sure someone has a manual and will give the real answer.

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That's pretty close to the old general rule I usually go by. It was .001 clearance for every inch of bore on a street bike engine and .0015 on a dirt bike engine.

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I just put in a 53.5mm piston with 0.0015 clearance and it felt a little loose :) Those small diameter pistons can be pretty tight compared to large dia. pistons.

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I just put in a 53.5mm piston with 0.0015 clearance and it felt a little loose :) Those small diameter pistons can be pretty tight compared to large dia. pistons.

Thanks, Tygen! I assume that .0015 clearance number you mention is in inches, not millimeters? A measurement of .001" = .03 mm. From what I've found out a common clearance for this size bore is .06mm or .002". Apparently it depends a lot on what the engine is to be used for, what the cyliner is made of, whether it has a liner and what the piston is made of. From what I could figure out with the answers for my setup the .002"/.06mm is at least safe, if not a very slight overkill.

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The diameter of the piston was measured just above the pin, so the rest of the piston is actually slightly smaller, thus the piston felt loose with only 0.0015" clearance. Other areas of the piston had 0.0030" clearance, so it's important to know the right place to measure.

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thanks, Tygen, and still waiting on piston to get here. I'm real close on the cylinder honing but gotta hold back and mic that piston like you say before I finish it out.

Whole lot of fun honing a 52.25mm cylinder all the way out to 53.0mm with a flat stone hone hah! Pa-a-atience.

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