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Andyru

Honda XR200 Piston to head clearance?

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Doing a rebuild on 1990 Honda XR200. With gasket and cylinder block together, if I rotate piston the outer edge of the piston potrudes slightly beyond the cylinder deck and even more so in the center of the piston. Any advise on what to do? I was think of a thicker gasket? Also, what should the piston to cylider deck clearance be? What's the best way to measure? Thanks!

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Its normal for the piston dome to be above the cyl.  There is plenty of room in the combustion chamber of the head for it.  Keep in mind that the head gasket basically adds cyl height.  I am not sure how to measure "slightly", but don't panic yet.

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I haven't got a measurement yet. I did some resurfacing and when I put the block in with gasket I noticed the outside edge of piston potrudes beyond block a little. However, with head gasket on it wouldnt hit the head. I have a thicker gasket I could put on to get the piston probably flush with the block. Im just not sure where it supposed to sit. Are there any clearance specs I should check for or is it not as critical for this kind of bike?

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The critical clearance is between the periphery of the piston and the cylinder head, the squish area.  There is some debate on best clearance because a small clearance creates more turbulence that helps combustion, but too small and the piston could hit the head at high rpm.  I assemble the cylinder/head/piston using old gaskets, no timing chain, cam lobes down (valve closed). Then insert a piece of soldier thru the plug hole so it reaches into the squish area, turn the engine thru one rev. Remove the soldier and measure its thickness.  Anything greater than 0.030" should be safe, I usually get 0.040". 
Do this again on final assembly to verify the new gaskets crushed the same as the old ones. 
If you use a Honda piston and gaskets you shouldn't need to do the check. But you said you planned the cylinder which made it non stock.

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Thanks for the help.  So I put in a gasket and got .0332 in. squish clearance and then I thought that with time and the vibration of the bike, the clearance would decrease over time as things settled. So I put in a slightly thicker gasket and got .0408 in. clearance. Then I thought I would check the valve to piston clearance out of curiosity.  I got a much bigger reading then I thought I would get.  I got .1775 in. clearance for the exhaust and .2256 in. for the intake side.  What are your thoughts?  Perhaps I did something wrong checking valve to piston clearance?  I used clay and did one full rotation of the cam sprocket.

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