139QMB Big Bore upgrade - Rings failed after only 600 miles.

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NCHippy
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Joined: Fri May 27, 2016 4:58 pm

139QMB Big Bore upgrade - Rings failed after only 600 miles.

Postby NCHippy » Fri May 27, 2016 5:29 pm

So my scooter left me stranded this week. It's a brand new TaoTao with the ever-present QMB139 engine and I put a Russo 80cc big bore kit on it a few days after I bought it. Ran great right up until the day it didn't ;)

After a couple of days fussing with the carb and deciding nothing was wrong with it and not having a compression gauge I pulled the valve cover off to be sure the tappers hadn't come loose and while turning the flywheel I noticed I could hear air escaping when on the compression stroke. So I pulled the whole head off and the piston rings were broken. Still in their slots but broken and a little stuck to one side also. cylinder wall seems fine, piston seems fine, just the rings are broken.

Can anyone suggest a reason why they would fail after such a short time?

New rings ordered hopefully I'm back on the road soon.

NCHippy
Posts: 2
Joined: Fri May 27, 2016 4:58 pm

Re: 139QMB Big Bore upgrade - Rings failed after only 600 miles.

Postby NCHippy » Wed Jun 01, 2016 8:39 pm

Well, new rings came and it runs great now.

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Areomyst
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Re: 139QMB Big Bore upgrade - Rings failed after only 600 miles.

Postby Areomyst » Thu Jun 02, 2016 10:33 am

There are several reasons that rings can fail - most have to do with lubrication. That said, with many of the off-brand kits, I see premature failures that simply seem to boil down to poor quality manufacturing. I would make sure that your engine shroud is installed and that the fan is doing it's job for sure... Use a good oil, etc...

~Josh
"The more a man learns, the more he realizes how little he knows."


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