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Powervalve-piston collision- why did it happen and how to fix it?

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I've got a 2001 YZ125. The left side power valve hit the piston ring and caused a nasty gouge in the cylinder wall. I'm not sure on how to adjust the power valve depth. What's the trick to that?

This top end had maybe 30-40 hours on it before this happened. Ran great up until it sputtered and died out on the trails.

Is a new jug (5MV-11311-00-00) the best way to get the motor back together?

Any advice appreciated.

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it certainly looks ugly, but IMO the companies dealing with replating also repair cylinders.

Have a look around Milenium, USchrome, Powerseal among others all repair them.

On the other hand, are you sure the powervalve hit the piston? It doesn't even looked touched.

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The piston "rocked" and the ring cought the edge of the port. (Too much wear)

I see this ALOT!

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Also looks to me that the ring caught the port, not the powervalve. I've seen that damage many times.

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Looks like you might have dropped a seed or 2 in there...

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Check your ports for a good chamfer. Sharp edges are bad.

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Thanks for all the advice guys! I guess my maintenance intervals weren't frequent enough... and I'm wrenching more than anyone else I know. 30 hours really doesn't seem like much to me, but that includes 2 races and a lot of WFO throttle.

Perhaps every 2 oil changes (20 hours) I should toss in a new top end? It seems a bit excessive.

The gouges in the cylinder wall are very deep, almost deep as the last time this happened. I just found a good place to have 2 stroke cylinders re-plated. I'll see if I can get it re-plated and keep it on the cheap.

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Thanks for all the advice guys! I guess my maintenance intervals weren't frequent enough... and I'm wrenching more than anyone else I know. 30 hours really doesn't seem like much to me, but that includes 2 races and a lot of WFO throttle.

Perhaps every 2 oil changes (20 hours) I should toss in a new top end? It seems a bit excessive.

The gouges in the cylinder wall are very deep, almost deep as the last time this happened. I just found a good place to have 2 stroke cylinders re-plated. I'll see if I can get it re-plated and keep it on the cheap.

Hours wise is always subjective which you know. It doesn't look like the powervalve to me either however, on my sons KX 85 it was an 01 on the PV was so loose it was touching the piston.

I took a dremel and trimmed it a tiny bit so that when it actuated it didn't come out as far.

This may be a little unorthadox but it has done the trick so far.

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Looks like you might have dropped a seed or 2 in there...

I didnt get this until further down the thread where I saw his username. Epic.

To the OP: I had the same thing happen to me, ring caught the port, and luckily, just smushed it into the piston.

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Don't be too quick to assume.....it is also a town in ca.

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Something got in there-Reed Screw ?-Filter/Airbox seal.Backward pistion ?-How is the end-play on your Crank/Rod ? YZ known for ring hitting skirt.

cylinder wear on Exhaust side

MyYZ025.jpg

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