pinched in piston ring by the piston

[codfish124]

OK so i did a top-end rebuild on my 96 cr125 and guess what, today in the middle of a mountain i lost all compression and the bike would not start. After towing me 8 miles with a cr250 witch is not fun and very painful if you ask me, but as my friends were off riding i took my cylinder off. I found that the piston had pinched the ring all the way in and that how the old piston was when i replaced it. So before i fork over more money to get a new piston i want to know how i can fix this so it don't happen again. It was pinched right at the exhaust port. I sanded it down and got the ring to move pretty freely in the piston and put it back together. With some help from the truck got it to start and run not to well but running nun the less any help is welcomed and thanked a lot.

[ossagp]

Yeah, the worst part of that scenario is that the CRF rider will never let you forget. I got towed in by a girl on an ATV once. Nice view during the tow in, but the abuse I took was horrible. I think that unless that is a brand new cylinder that it partially seized and the piston damage took place at the part where the cylinder was hottest, ie right on the bridge.

Does the face of your piston have a hole drilled in it that lines up with that bridge.

next thing to look for his a leak between the head and cylinder. If you are getting any coolant into the cylinder during running, it goes steamy and washes the oil off the face of the piston and you can get just what you are talking about. Something the crown of the piston will almost look sand blasted right up in the front 3/16 of an inch or so of the crown, all nice an clean and the rest is blacker or chocolate even.

[vr4king]

Dumb question but what is "pinching a ring" mean

[codfish124]

It is at the bridge and there is no hole in my piston there what do I do to pervent this in the future

[codfish124]

Originally Posted by vr4king

Dumb question but what is "pinching a ring" mean

The piston closed in on the ring pinching the ring in place

[Blitz393]

What brand piston are you running? Every Wiseco piston that I have used either had a small oil hole at the front of the piston or had instructions to drill one yourself. the bridge in the exhaust port has a much smaller surface area and volume compared to the rest of the cylinder, and therefore is more apt to getting Hot, and doing it quickly. Check inside the box the piston came in and it should have a picture of the piston and instructions on how to make your own oil holes. These holes are in place to (obviously) lubricate a normally hard-to-lubricate area, and to prevent the kind of damage that you encountered. Also check your service manual, if you have one.

another problem that kind of sucks to hear is that simply from the fact that this has happened before, it is likely that the super thin Nikasil/ceramic/electroplating (whatever it is they put on CR's... lol) may have worn off or been scraped off. not only does this create a Hotspot and therefore a weak link for the future, it's not easy to fix... [Only registered and activated users can see links. ] has decent pricing and does awesome work, i've used them before. you may be able to check your local bike shop salvage yard to simply replace the cylinder, however i wouldn't do anything until you post pics so we can see the carnage ourselves

-Rob

[codfish124]

theres what the old piston looks like and the new one looks the same i didnt see any thing on drilling a hole ill look

[codfish124]

Guess I didn't read the back side of the piston papers and didn't drill the hole

[ossagp]

How did I know that? Bikes with those skinny little bridges like that really need the holes. With the mix levels some people run it is very important.

[codfish124]

Thanks for all the help I guess the next piston should work better

[vr4king]

How many hours you get on it before it did this?

[codfish124]

Maybe 6 I don't know they were prity hard

[codfish124]

well well well the wiesco piston i put in had holes drilled in it so i guess im back to square one what elce could cause somthing like this th happen? i put a porX piston in caus that what it had befor and it lasted about a year the proX had no holes so i didnt put any in it. it started right up and ran good i think im going to realy break this one in

[ossagp]

The ProX is cast piston much like OE. I thought you had an easy answer there. Look again for coolant leaks. About a thimble full in in ten minutes could do it. That is the first place a piston will start to seize. Look for airleaks too. if you have a leaking seal, they get worse, and do it faster each time. same with a leak around anything else, though leaks on the nonmoving parts don't always get progressively worse like a seal will. Did you change mixes too?

[codfish124]

i did try a differnt oil it said to mix it way litter i didnt i did mix it a little lite but 36:1 not 60:1 like it said i also got a bottle of synthech it was really thick like sryup i dont know about this stuff i was told it was really good i think i might try it at 20:1 i dont know

the water level was full i dont think it it was leaking. the cylnender look in ok shape no big mars i hit it with some 800 grit sand papper didnt see any discolorations look like the nickel was ok


im going riding tonight so i think im going to mix it really heavy with oil the frist tank then probly stay away from synblends and stick with HP or somthing i dont know lol

[ossagp]

We used 20-1 in the 144 kitted cr125. I don't necessarily think that is your problem though. Broke all ours in on mx courses where the throttle wasn't on maybe as long as you had yours on. Check for the leaks, run it in a without the long hills. (two seconds of wide open at anytime in the first hour should be enough.) We put ours together dry for a fast seat. The bearings are really wet when we put them together.

That part of the cylinder seems to run the hottest, deforms a little from it etc. Partial seizure can be the result. maybe go up a size on the main jet to breakin if you think you may be prone to running it hard early on.

[codfish124]

well the frist 4:30 were on the mx track and let me tell you it ran like a raped ape so we went up to the mountans and the frist trail it died im headed to the track tonight after work wether permitting so i gues wish me luck

[misfit]

my old YZ 125 used to do that to me... 1st time thought maybe bad piston, 2n'd time it scarred the walls and beat metal into the dome... got it fixed up and re-nikasiled and never had a prob till i sold it.... never found out what the actual problem was, but there's a solution.....