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another dumb question

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new piston...fresh bore....with the piston in the cylinder, how much "slop" should there be?...fighting a smoking condition on older xr80...replaced valve seals, but i noticed the piston seems kinda sloppy in the cylinder...would a bike even run if the piston was 1 size too small? (the bike did run and seemed to have good compression with this piston in it)...thanx guys

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The only "dumb question" is the one that you don't ask :thumbsup:

new piston...fresh bore....with the piston in the cylinder, how much "slop" should there be?...fighting a smoking condition on older xr80...replaced valve seals, but i noticed the piston seems kinda sloppy in the cylinder...would a bike even run if the piston was 1 size too small? (the bike did run and seemed to have good compression with this piston in it)...thanx guys

I'm not sure I understand your question. There should be zero "slop" only a couple thousands "clearance" in the piston / bore.

Is the above quote referring to one bike with a problem or two seperate bikes?

You claim to have a "fresh bore." The machinest should have had the piston in hand and checked for proper clearances while he was boring the cylinder.

Unless you are going on someones word that the cylinder was just bored to XXXX and put a new piston/ring set that size in it without fitting the parts and checking the ring end gap, it's anyones guess what you put together.

would a bike even run if the piston was 1 size too small?

IMO if the piston and ring set was "one full size" smaller than your bore (unless the bore was so worn out that you somehow managed to stuff the next size piston and rings in it), there would be no way that you would get it running by kick starting it! Maybe if you pushed it real fast or towed it behind a car it would fire and run if you kept it wound, but in no way would it have "good compression."....Karl

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As Karl stated, most machine shops will bore, wash the cylinder, hone it, wash it again, and then they will take the piston you are going to use, and slide it through the cylinder, along with a long .002 or .003 feeler gauge. If the piston slides through somewhat easily, the piston is the correct size for the cylinder. If the piston slides through real easy, or there is slop, the piston is not the right size for the new bore.

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