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Discussion Starter · #1 ·
In the process of rebuilding a 94 polaris xlt 580 from the crank up, just got my pistons in for a 40 over bore. and one piston is measuring up .10 under spec and the guy from the parts store said it will be fine to put those in. just give me some feedback . All the pistons are measuring in at about 35 thou. over bore. and one at 25. over bore.
 

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IMO, that's way too big of a gap. 10/1000 of a inch is 1/100 of a inch which is pretty big in something as important as pistons. Someone may have something else to say but that's my opinion.
 

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Discussion Starter · #5 ·
well i will be getting each cylinder bored to match the piston that will be going in that cylinder. i just didnt know if one being 10. thou. under the rest if that would make a difference in how it runs and reliablity
 

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Not sure about that one. 10/1000ths of a inch wouldn't be much weight but by the time it gets to 8000 RPMs it will be pretty significant.
 

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Agree with the others, get the correct size. Even if it's only say 5 grams difference, you just threw your whole engine out of balance. If you're out of balance, you are going to tear up bearings, and maybe the crank too.
 

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Who did you get the pistons from? They'd be getting a heated phone call from me! They probably should all be balenced together, just look at the inside of the pistons, most reputable places balence them all together as a matched set. However, they are usually matched bore size together also! Sounds like it was someones last day at the piston manufacturer!
 
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