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Discussion Starter #1
First off, I don't ride a bike. I have an 08 1000 in a dirt car. Running c85, tuned, APE sprockets, and air stacks. Some background into my issue. 2 years ago, I was rebuilding the motor and found 2 burned/melted pistons. They burned right around the valve recesses. Replaced them, ran great, cool. Blew that motor (unrelated issue). Got a new motor, ran it, it's been awesome. Seasons starting in couple months, checked compression, 200 on 3, 105 on 1. Leak down test shows it leaking past piston. Awesome. Ordered new piston and rings. Here's my issue. I pulled the head off tonight, and the piston looks fine. It doesn't look like the other 2 did. Now I'm hesitant to crack this case open to change the piston. I was wondering if anyone else has run into this. I can't see the rings sticking, but I guess it's possible. Any input would be appreciated. Thanks.

21X.
 

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Captain Obvious ... because obviously it’s obvious
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First off, I don't ride a bike. I have an 08 1000 in a dirt car. Running c85, tuned, APE sprockets, and air stacks. Some background into my issue. 2 years ago, I was rebuilding the motor and found 2 burned/melted pistons. They burned right around the valve recesses. Replaced them, ran great, cool. Blew that motor (unrelated issue). Got a new motor, ran it, it's been awesome. Seasons starting in couple months, checked compression, 200 on 3, 105 on 1. Leak down test shows it leaking past piston. Awesome. Ordered new piston and rings. Here's my issue. I pulled the head off tonight, and the piston looks fine. It doesn't look like the other 2 did. Now I'm hesitant to crack this case open to change the piston. I was wondering if anyone else has run into this. I can't see the rings sticking, but I guess it's possible. Any input would be appreciated. Thanks.

21X.
If your ringland is cracked, then it may look fine and not perform fine.
 

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You should listen to me. No, seriously, listen to
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How about putting some oil, the thicker the better, into the bore to slow down leaks past the rings and rechecking the compression? Unfortunately that means putting the top end back on.

Any chance that the cylinder wall is cracked? You would have been getting air bubbling into the coolant reservoir if so. Maybe some coolant seeping into the combustion chamber.
 

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I put the top end back on already just to recheck my readings (again). Same thing. Oil helped but it's still about 50% leakdown. Cylinder walls look immaculate. I'm gonna break it down tonight and see what it looks like. One way or another, I'll know something. I'll keep you updated.
 

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Discussion Starter #9
Great news! Did you have the tune checked after the previous piston damage?
I did. Especially since it was a different motor. Well, same motor, but different motor. Lol. I guess you know what I mean. I'm not sure why they stuck. I thought that kind of thing was a thing of the past but I guess not. At least I know the other ones are good. Less than 2% leak down.
 

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You should listen to me. No, seriously, listen to
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I'm grasping but I wonder if you have a cooling problem. You presumably already measure the coolant temperature. Do you have a way to measure the oil temperature?
 

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The stuck rings are from the C85 it dries the upper cylinder. I asked about the tune because C85 and E85 timing maps could be tricky to tune. I've seen cars tuned perfectly with it on the dyno only to end up with some knock or detonation on the road which could explain the cracked pistons.
 
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