My RM125 is in Trouble! (Legal Karma)

[NodnarbRS]

So I was riding my 1997 RM125 on my usual trails and I got a little bored so I hopped on the road to go somewhere else (the bike is NOT street legal) All was fine on the twisty little back roads but I found myself on a strait stretch that was posted 55 mph. I took the little guy up to 69-70 a couple of times (iphone speedometer app) and then it just died. I pulled off the road and into the brush a little ways. The kickstarter was a bit stiff but it soon turned over ok, but it was lacking in the compression department. It wouldn't start so hid it and came back with a truck. I went to put a new spark plug in and found the existing plug a little loose and it had no gap. I stuck a new plug in and with much trouble it started a couple of times. I let it idle for a few minutes but when I gave it some gas it would just die or backfire and die. It sounded different too. So did I have a partial seizure? Do you think a top end rebuild is all I need? Can you deduce anything? This is my first twostroke and I've never worked on one before. Advice is appreciated!

This what I get for riding on the road!

[rideon123]

No compression equals piston ring. Check piston with micrometer. Usually get away with 2 rings per 125ccured piston. I believe a westco piston comes with 2 ring and 1 piston even though 125 only needs 1 compared to 250ccured which requires 2 and a head gasket. Can reuse o ring seals in top of cylinder hesd cover if not degraded. Also look for cylinder bore defects. Rings dont last forever. Especially if u ride it like u stole it

[rideon123]

To do it right. Micrometer is $15 ring and gasket probably like $30.U need book for torque specs. And would be nice to have an in. Lb torque wrench. If your gonna work on your first top end, couldnt be starting with a better engine, other then a suped up lawnmower. watch a youtube video on top end for 2 stroke for a nice visual starter.

[JFortner5]

Yep sounds like top end time. You'll probably want a new ring and piston especially if you don't know when it was changed last.

[Derfboy]

If the spark plug had no gap when it came out but it had a gap when you put it in and it was backfiring I suspect you cooked your wrist pin bearing along with the top end. When you take it apart and you take the wrist pin out of the piston put rags over the crank so none of the needle bearings fall into the crank. This would explain this because if the wrist pin bearing goes out then the piston has extra room to move up and down on the wrist pin so it could have came up and smashed your spark plug. My Yz did this with the same Symptoms.

[handreasen]

just replace the valve stem cap, will run like new! Remember it is a 2T they never need any work, run for ever!

[Qqqqqqqqqqqq]

It wasn't the Road Riding .. Ringing its Neck did the damage

Edited July 28, 2014 by ITS CHOOKEN

[Beau 88]

just replace the valve stem cap, will run like new! Remember it is a 2T they never need any work, run for ever!

?  I looked at that like Wtf ! Then seen it was you  ? good chuckle .