Any ideas

[dirtgod 81]

I am having a problem with an 89 Trx250r.

Ok we have rebuilt the top end, and about 1 hour after riding, the top end locks up!!!! What happens is the front side of the piston and the cylinder lock up. The piston gets so hot, the rings melt to the piston. What we are thinking is that the rod is bent. We have rebiult the top end 2 times and same result both times. Any ideas would be great!!!!!

cooling problems?? :rolleyes: :confused:

[A A R O N]

If you have an aftermarket cylinder thats a powervalve, it could be partially stuck open....thats what happened to a friend's yz125. It melted one side of the piston, but the other side was fine. If that's not the case....replace the crank bearings/rod like you said.

[250r4life]

the powervavle being stuck open will not cause the piston to seize... it will just work like a non-pv engine

[A A R O N]

Originally posted by 250r4life
the powervavle being stuck open will not cause the piston to seize... it will just work like a non-pv engine



Aaahhhh, but i beg to differ. I don't know what else would influence my decision that it would other than a real life experience where it did:chinese: There may have been other factors involved, and i assume his semi-low oil-fuel mix ratio had something to do with it, but after the pv was fixed and a new piston was put it and he ran the same ratio as before in it and didn't change a thing, it ran fine. I could be wrong though.....theres never ever a case where a problem with a bike defies what usually happens:rolleyes:

[Scott-300ex]

Wut kind of gas ar you running?

Just run 93 with your oil and STA-BIL (I suggest)

I've seen Alcohol and straight race gas do this before.

It makes it run REAL hot. You don't even need that cuz it won't help anyway.

[250r4life]

Originally posted by A A R O N
Aaahhhh, but i beg to differ. I don't know what else would influence my decision that it would other than a real life experience where it did:chinese: There may have been other factors involved, and i assume his semi-low oil-fuel mix ratio had something to do with it, but after the pv was fixed and a new piston was put it and he ran the same ratio as before in it and didn't change a thing, it ran fine. I could be wrong though.....theres never ever a case where a problem with a bike defies what usually happens:rolleyes:

how in the world would a stuck pv cause it to seize?

[A A R O N]

Don't ask me, I don't know how it did it, it just did:confused:

[250r4life]

Originally posted by A A R O N
Don't ask me, I don't know how it did it, it just did:confused:

think again buddy...

[LT250RMan]

If the power valve was stuck open it just would lose some bottom end power thats it,, It would'nt melt the piston

[250r4life]

ive already tried to tell him

[WareRacing]

Originally posted by Scott-300ex
Wut kind of gas ar you running?

Just run 93 with your oil and STA-BIL (I suggest)

I've seen Alcohol and straight race gas do this before.

It makes it run REAL hot. You don't even need that cuz it won't help anyway.


actually, ALKY makes the motors run cool. thats why the carb drip water...is cooler than the outside air. you can actually make a ALKY motor run cooler my adding more fuel to it.

[bananas]

A couple Questions.

When you rebuilt, did you use a new piston?
Did you get the clyinder bored out at the same time?
Did you give the piston and the clyinder to the guy that did the bore job?

If you answered is NO to any of theses questions, you can now see your problem.

The clyinder is not round or bored out to far..


One more for you. Are you 100% sure you have a 89 bottom end?

[zedicus00]

what kind of break in did you do? 1 hour after what type of riding?