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shouldabeen

rings stuck

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06 yz 125 all fresh 2hrs run time w/fresh air filter. yes mix correct and filter dry what would make the ring stick??

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rings stick, as in the piston siezed up?

no piston moves freely had no compression took the pipe off to look int cylinder and look like the ring is stuck with a very small scuff at the ring groove on the piston in the exhaust side looking in have not pulled head yet to see how the rest looks. I just wonder if the power valve hit the ring?

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look for signs of detination around the piston edge ,, or the PV hit it like you said

what or how would the power valve be allowed to do this? ok what if it was detination that mite be a bad ignition system?

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mine did the same exact thing, new cylinder, head and PV and it still did this, its like the ring was pressed into the cylinder and has no compression. i have 3 pistons like this, it happens between 6 and 12 hours of run time. same exact marks on pistons, can it be a bad rod or something?

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ring was pressed into the cylinder and has no compression. No mine the ring was stuffed into the piston ring groove on the piston.I am sure the crank and bearings are good.

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Did you check the ring end gas before installed the top end? did you check for the clearance for the ring in the groove of the piston? any tight spots should have been filed down very lightly. could have been out of spec and when it got warm it jammed up on the exhaust side because that is the hot side...

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Carbon build up on the exhaust side might cause the rings to stick.

nope like I said all fresh all cleaned pro level even power valves clean and exhaust cleaned inside also and even had the cylinder replated and put back to standard bore size.

After two machine shops the only conclusion we can come up with is the pin inside the ring groove was pressed to far into the piston not leaving the pin out far enough to stop the ring from rotating in the ring groove, I am trying to get Vertex to give me the specs so I can confirm to this theory.

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Did you check the ring end gas before installed the top end? did you check for the clearance for the ring in the groove of the piston? any tight spots should have been filed down very lightly. could have been out of spec and when it got warm it jammed up on the exhaust side because that is the hot side...

Vertex piston I think was out of tolerance but yes piston OD checked and cylinder ID checked 2 thous of clearance and thats about how much it will expand so should of been good. ring gap also good. as stated waiting on Vertex specs to check the pin depth inside the ring groove to insure it was not pressed into the inside of the piston to far. thus allowing the ring to spin around and that would make one side a couple thous to large and blam its gona catch a port some where.

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nope like I said all fresh all cleaned pro level even power valves clean and exhaust cleaned inside also and even had the cylinder replated and put back to standard bore size.

After two machine shops the only conclusion we can come up with is the pin inside the ring groove was pressed to far into the piston not leaving the pin out far enough to stop the ring from rotating in the ring groove, I am trying to get Vertex to give me the specs so I can confirm to this theory.

My bad.

A very odd situation though. I was at my local shop yesterday and I was shown a brand new Wiseco that looked like it had a valve cut away in it for a 4T. It was for a yammi 2T. They are waiting for a rep to come and check it out, but they think one of the machining tools caught it and it was overlooked by the QC people.

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My bad.

A very odd situation though. I was at my local shop yesterday and I was shown a brand new Wiseco that looked like it had a valve cut away in it for a 4T. It was for a yammi 2T. They are waiting for a rep to come and check it out, but they think one of the machining tools caught it and it was overlooked by the QC people.

Maybe its a piston for the new DI two strokes! :p

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i got an answer for my bike today from a yamaha tech i know.

maybe the same for you, the bridge in the cylinder expands and sometimes new cylinders or recoated ones they dont shave down the bridge like 1-2 thousandths of an inch. so when its gets hot enough it will nick or press the ring into the cylinder. That is what i was told and it makes since. hopefully me typing it makes since lol

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i got an answer for my bike today from a yamaha tech i know.

maybe the same for you, the bridge in the cylinder expands and sometimes new cylinders or recoated ones they dont shave down the bridge like 1-2 thousandths of an inch. so when its gets hot enough it will nick or press the ring into the cylinder. That is what i was told and it makes since. hopefully me typing it makes since lol

HONING IT SHOULD TAKE THAT MUCH OUT AND I DID THAT WITH A FULL LENGTH HONEING TOOL B-4 RE-INSTALLING THE NEW PISTON AND FEELER GAUGES USED TO CHECK CLEARANCE,RING GAP ECT ALL MEASURED AND PISTON CHECKED ALSO. SO FAR 2 MOTOS AND 20 PRACTICE LAPS STILL GOOD. I THINK IT WAS STILL THE PISTON. BUT I AGREE IF THAT WAS THE CASE WOULD DEFINALTLY CATCH THE RING.

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HONING IT SHOULD TAKE THAT MUCH OUT AND I DID THAT WITH A FULL LENGTH HONEING TOOL B-4 RE-INSTALLING THE NEW PISTON AND FEELER GAUGES USED TO CHECK CLEARANCE,RING GAP ECT ALL MEASURED AND PISTON CHECKED ALSO. SO FAR 2 MOTOS AND 20 PRACTICE LAPS STILL GOOD. I THINK IT WAS STILL THE PISTON. BUT I AGREE IF THAT WAS THE CASE WOULD DEFINALTLY CATCH THE RING.

What tdb is saying is that the exhaust bridge needs a few thousands MORE clearnace than the rest of the cylinder. If it were honed full length to the same bore diameter, then that just caused your problem. Hit up the Honda 2 stroke forum and look around, this is a very common battle with the CR125.

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We had a brand new honda cr 80 cylinder that did this. The bridge would eventually cut a section of the piston away. It was never properly relieved from the factory.

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why would it not catch on the intake ports? If its all the same on the ID then all ports should grab the ring not just one? A full length honing tool would or should leave it all the same so I cant see why the exhaust port can grab the ring and the intake side wich would be the same not catch it also. I wanted couple thousandths clearanc on the whole cylinder not just at the exhaust port, as the piston was to tight to begin with but for now the new piston did have the pin inside the ring groove that was extruded more than the one that was in it.

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