Broken Piston Ring

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Broken Piston Ring

Postby Druck1 » Tue Aug 10, 2010 9:09 am

I installed a brand new YT60 piston/cylinder set-up on my QT50. Stock head, cone type air filter and stock jetting, Boysen reeds, 32:1 premix.
I ran it for only about 5 miles and it died and would not re-start. Trouble shooting from the carb on in revealed that both piston rings broke off about 1/2 inch from the ends. Plug is showing a lean burn. Any ideas on cause? I don't want a repeat!
Thanks
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re: Broken Piston Ring

Postby John » Tue Aug 10, 2010 12:02 pm

What was the rings end clearance when installed? Expansion is a killer if not sized right! Google "ring end clearance specs".
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re: Broken Piston Ring

Postby mopedlar » Tue Aug 10, 2010 12:43 pm

I'd take a very close look at the bore of the jug, specifically, the spot where the rings snapped. Any kinda gouge, pit, casting defect, etc. in the bore can cause a ring to snap.
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re: Broken Piston Ring

Postby Druck1 » Thu Aug 12, 2010 8:39 am

Thanks for the replies and help. I think the rings expanded and somehow caught the edge of the intake ports which caused the break.
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re: Broken Piston Ring

Postby John » Thu Aug 12, 2010 5:00 pm

That is why you need to fit them with the proper clearance. There are charts on the interweb giving you what you need to relieve the ends by. Out of the box doesn't do it!
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re: Broken Piston Ring

Postby pete in pa » Wed Mar 21, 2012 6:35 am

I know it's 2 years old but for future reference I just did the 60 upgrade. Even with a new cylinder straight from Yamaha I thought the port edges were too sharp. I smoothed them with a file.
The cylinder had a nice crosshatch to it though.

Rings must be checked for end gap mine were fine.
rings must be indexed to the pins in the groves correctly.
The piston has an arrow on the top, this points to the exhaust.
1981 Yamaha QT50: Yamaha 60cc hop up, PW gears, stock pilot, 75 main, red Uni filter, BP7HS plug.
2006 Honda ST1300
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re: Broken Piston Ring

Postby xrongor » Wed Mar 21, 2012 6:16 pm

the times i have seen this it has been because the piston and rings were not coated with oil.
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