Apr 26, 2007
My beloved CR 125 was working well then kind of stalled on me mid way through a corner of a MX circuit. I can not move the kick start . I can change gears and roll it in neutral. Have I siezed the engin and if so does that me a complete replacement is the best action??


Apr 18, 2006
First off, this was the wrong spot to post this question. It belongs under the general repair section.

But to answer your question, yep, that is a classic seized engine symptom.

I am not sure what you consider a "complete replacement" to be. A new bike? That would be a bit drastic!

What you need to do is a "top end" rebuild. Prior to a sieze this can be as little as a light hone and a new ring. After a seize it generally means a new piston and a cylinder bore or re-plate.

The first thing that you want to do is to pull the spark plug and spray some WD-40 or some light penetrating oil into the cylinder. The objective is to get the piston to unstick from the cylinder, otherwise removing the cylinder will be a bitch. Let the oil soak for a day or so then shift into high gear and try to bump the piston free.

Once you can get the piston to move in the cylinder then it is a matter of tearing the top end off. This generally requires the removal of the gas tank, the pipe, and radiator hoses (if water cooled). On some bikes you may need to remove the carburetor and reed cage.

The linkage between the power valve and governor needs to be removed. The power valve separates and each half is withdrawn from its respective side of the engine. A few nuts on the top and the cylinder head comes off. Four nuts down lower and the cylinder comes off. Shove some rags into the hole around the rod to keep stuff from falling in (like the clip you need to remove next...).

Remove a wire clip from the side of the piston and then you can push the wrist pin out of the piston and remove it from the rod. No need to remove the rest of the engine from the bike.

Now you take the pieces to your favorite bike shop (or directly to a machine shop if you know of one) and have it fixed. Cylinder hone/bore/re-plate, new piston and ring, new gaskets, maybe a new wrist pin bearing. Figure $200 to $300 to get the bike running again.

When you know what you are doing that process would take about an hour, maybe less. For the first time, give yourself all day, take your time and be careful.

Reassembly is the reverse of the above.

Get a manual for your bike, you will need it!

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