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Discussion Starter · #1 ·
My son just bought a '09 Renegade 80R with a blown top end for short money.
We tore it down and found a blown piston on the PTO side.
I'm preparing to replace the cylinders and pistons wit MCB components.
I'd like to get some opinions on the failure from you guys who may have some experience.

The Piston has a section of the ring broken out and it looks like there is a small area where the aluminum melted from the ring groove to the deck (see pictures)
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The cylinder doesn't look too bad, there are a couple nicks where is looks like the the broken ring exited the exhaust.
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There is also some discoloration on the tops of the conn rods and the wrist pins where exposed.
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I hoping you guys can tell me if this is typical or if I have something else going on ( air leak, overheat, ect)
I sure don't what to rebuild the top end and have this recur.
BTW - the mag and PTO crank sides will get new grease and seal.
Thanks for any input.
 

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I agree with smurfy it looks like the pin that locates the ring failed and allowed the ring to turn until it got into the exhaust port and caught. It’s one of those things that happens with age. Detonation or overheat can cause it prematurely. Looks to me like the rings had a serious amount of blow by. That can lead to increased piston crown temps, and detonation at the locating pin area. You may be able to re use the cylinder. The rods look typical and aren’t a concern to me. But a thorough inspection of the crank would be wise.
 

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The 500ss motors are known to somehow push the locator pin in and allow the ring to walk and catch the exhaust port. Happened twice on the same motor to me. I was told it was detonation. Even though the engine is made to run on 87, the quality of it is bad. After I did the top end I started running higher grade and it felt like it ran crisper. So I would alternate gas grades. Us 87 one fill up and higher for the next
 

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Discussion Starter · #6 ·
Thanks for the great input.
The locator pins on both pistons were recessed, good observation.
It has the stock jetting 480 main, 17.5 pilot, maybe the prior owner didn't use premium.
I did clean them before reinstalling them.
Anything else I should look for?

Thank you all
 

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I would probably get a very fine half-round file and blend out that nick in the exhaust port. Just remove the raised metal and make it smooth again. Having said this, I have no experience with this particular engine, so others here might give better advice. Just saying what I would do if it was mine.
 
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