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Mr. Carts 02-10-2012 11:38 AM

1996 RM 125 Blown Head Gasket
I could use a bit of help.

I am fixing a 1996 RM 125 for a young fellow. It is his first bike.
He got it in a non running condition.

I am a long time rider starting with my first bike a Hodaka Ace 100 but my newest two stroke is a 1972 Yankee Z.
I have worked on many air cooled Two strokes but never a watercooled one.

His bike had no compression so I pulled the head.
I can see were the steam has cleaned off the carbon on the piston so I know the head lost its seal.

Thesewatercooled bikes only have two O Ring sealing the head? I did not see a copper head gasket.

How is the best way to insure that the sealing surfaces are going to reseal once I install the new O Rings?

The Cylinder is stilll showing cross hatching on the cylinder wall. Can a Nikasil cylinder be honed like a steel cylinder?

Is there a PDF online of the service manual?


pvangel 02-10-2012 01:17 PM

There are only orings to seal the head, you should check to see if the head is warped from overheating otherwise the seal should be fine.

Nikasil should not be honed but i have used one by hand to clean it up.

Google is your friend on the manual.

Good luck with it, fun bike!

gplracing 02-10-2012 02:41 PM

I'm guessing that if it is o-ringed for that age bike it is a modified head, they came with a gasket from stock but had a real odd set up with little to no squish band.

What does the piston look like? it is very common for the exhaust side of the piston to be damaged from water entering the chamber if it was running. Check the rings they maybe stuck in there grooves, and they go out of shape quick.

I o-ring a lot of heads, the o-rings tend not to fail in fact I've never had one fail. It will be a reaction to something else that will course the o-ring seal to fail.

So you may have to find the course before you can fix the problem.


pvangel 02-10-2012 05:00 PM

Most "modern" 2 strokes have the o-rings instead of the copper head gasket and this bike is one of them, I checked the parts pic and indeed there are 2 o-rings.

gplracing 02-11-2012 04:54 AM

Yep I got that wrong and indeed it is machined from the factory with o-rings. I had the one in the pic a few years ago and blindly assumed they would be the same lol.


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