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Discussion Starter · #1 ·
I have a 03 mountain cat 570.Last year on the magneto side,the piston ring pin broke which turned the rings and eventually hit the exhaust port scoring the cylinder and wrecking the piston.That was 600 miles ago.Last weekend I put 125 miles on and encountered problems starting it up.After sending it to the local dealer they discovered the same thing happened,but on the clutch side.Does anyone have a reason or idea why the pins are breaking?
 

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I believe this was a common problem with the older 550's. I heard they needed new pistons every 3000 miles. I didn't know it was a problem with any other engines though. How many miles do you have on the sled??
 

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Well, firstly, I don't know anything about rings turning, but I siezed mine a coupla years ago midrange lean. But the '02's were leaner midrange than the '03's, so I added the '03 needles. It's still lean in the midrange, but better. Anyway, after first sieze, on the mag side (and not very badly siezed even), I put it back together and the crank was out of time. Don't know if that will make a diff. or not. Other thing on mine was the case halves fretting, and had chunks of alluminum on the crank outer races that had come off the crank saddles...this means the case halves are not holding the crank still in the bores... I don't know if this will cause your rings to turn... Last, who did your jugs? The jug I got from millenium was far superior in workmanship than the new stocker from AC.

I would say, send the jugs to Millenium, get the crank looked at, and put it together and watch the jetting and oiling. I put mine together with locktite on the crank saddles because of the fretting. I also located ARP case studs that will work, but didn't take time to get them and don't have those numbers handy. PM me if you want them.

Good luck,
John
 

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Yea this happens to a lot of Fan Cooled motors, What was the temp you were running that thing? I dunno
 

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Discussion Starter · #6 ·
The day it happened it was -15c,but that's not saying the pins didn't break a couple hundred miles before then at a warmer temp.
 
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