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Big Bore Failure

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TS 250's a 2-stroke. Backwards piston probably caught a ring end in a port.

Yup that's what happened with mine , a first lesson as a kid and internal motor work . The cost pain goes away once the motor is done and you can enjoy it , you never forget it though so it's something not messed up again.

Edited by jjktmrider
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I think I timed the cams with the chain loose... Jesus...

I can't even remember.

Live and learn, nothing you can do about it so don't harp on it. Don't beat yourself up over it.
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Live and learn, nothing you can do about it so don't harp on it. Don't beat yourself up over it.

Thanks man. I'm looking at engines on ebay now. I might put the hotcams in whatever engine I get but I'll prob skip the big Bore for a while.

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Incorrect valve timing would explain the damage, certainly not much room for error and she lets you know pretty fast if everything isn't spot on.

Bloody shame, but thanks for passing this along and reminding everyone here to exercise extra care with cam timing.

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I've thought about the possibility of buying a new engine from eBay and decided that, if the worst happened, I'd probably get mine rebuild. At the least then you can choose your own parts, will have a legit straight new engine and aren't potentially buying someone else's headache

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I've thought about the possibility of buying a new engine from eBay and decided that, if the worst happened, I'd probably get mine rebuild. At the least then you can choose your own parts, will have a legit straight new engine and aren't potentially buying someone else's headache

That is true. I think in this case he should really think hard about a new motor. When things fail like they did for him it tends to be hard to rebuild. If the inside of the case gets damaged there's not really much repair you can do.

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Since both exhaust valve heads broke obviously the exhaust cam was not timed properly. Don't beat yourself up too much anyone that works on their own bike is going to make a mistake someday. That is how you get smarter.

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That is true. I think in this case he should really think hard about a new motor. When things fail like they did for him it tends to be hard to rebuild. If the inside of the case gets damaged there's not really much repair you can do.

I may have someone interested in the bad motor... Just gonna find one on eBay or something and get it back on the road. I obviously can't do the big Bore right so I'm not about to split cases myself... And by the time I pay someone to do it all I might as well have bought one anyway.

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I've taken my head off my bike twice now. To verify I get the timing 100% correct I mark the timing chain and teeth in cams with a sharpie so I get the timing 100%. Gotta remember to keep tension on the chain and you should be good

I've taken my head off my bike twice now. To verify I get the timing 100% correct I mark the timing chain and teeth in cams with a sharpie so I get the timing 100%. Gotta remember to keep tension on the chain and you should be good

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