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Question about XL600R Piston Clearance- Need Expert Advice

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I have a 1985 Xl600R, in the process of doing a complete engine rebuild. I am using a first over (.25) OEM cast piston. Honda service manual gives specs of .0004" to .0016" for piston clearance (thats four ten-thousandths!). Just about every other engine I've done seems to have a spec of .002" to .003". I dropped the jug/piston off at the machine shop yesterday and talked with the owner about it. He and I both seem to think that the OE specs are too tight. I don't want to risk piston seizure and have to pull this thing apart again. I also don't want it to burn oil and wear out too quickly. OE spec for maximum piston clearance is .004". Does anoe have experience building these motors? What would you recommend for piston clearance? I was thinking .002".

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Honda's spec for the 650L(same bore size and cylinder type as the XL600) is similar: 0.0008-0.0020" as standard and 0.005" for the service limit. I think aiming for 0.002" would be alright.

Cast pistons typically have a higher silicon content and don't expand as much as forged pistons and 0.002-0.003" is more in line with forged piston clearance.

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Honda's spec for the 650L(same bore size and cylinder type as the XL600) is similar: 0.0008-0.0020" as standard and 0.005" for the service limit. I think aiming for 0.002" would be alright.

Cast pistons typically have a higher silicon content and don't expand as much as forged pistons and 0.002-0.003" is more in line with forged piston clearance.

+1.... J.E. specs the clearance at .003 for the piston i used...

I`m thinkin you guys are right at 2 thou....0.0008 is really snug...

B

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You really don't want to much clearance on a cast piston, I would use the Honda specs.

As we all know forged pistons expand two times as much as cast or a fuzz more depending on the silicon content.

To much clearance on a cast piston will cause skirt and bore issues. OEM pistons have the highest silicon. They have the tightest installed clearances of all and least noise in a cold start.

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