YZ250F Miscellaneous top end questions

This weekend I'm going to be putting my 2006 YZ250F top end back together, and have a few questions.

1) I bought a piston kit for an '08 YZ250F. It has an arrow on top of the piston. Can someone verify for me which direction the arrow should point?

2) Valve shims - I'm curious, do valve shims just sit "loose" inside of the buckets? When I pull a shim from a bucket, and then reinstall it, do I just set the shim back in the center of the bucket?

3) Cleaning parts - I was told to use a scotchbright pad and bathroom cleaner to clean all of the parts before assembly. Just doing the top end (not doing valves), which parts should a clean and what should I not clean? Is bathroom cleaner ok?

4) Grease - the manual talks about putting some kind of grease on certain bolts? It looks like the head bolts, etc. What type of grease is this? Is it necessary?


Well usually the arrow points to the exhaust(at least on a 2-stroke), but just look at the piston and find which side has 3 divits on it and thats the intake side.

The valve shims should be put on top of the valve spring and not in the bucket. place the shim on top the spring(like where the retainer is) and make sure its nice and snug in there, then place the bucket on top.

As far as cleaning parts usually use gasoline or just wipe them off with a rag.

And as far as grease goes I dont know. I never use any and if I did it would probably just be the same grease I use to grease my linkage

MX called it.

I use lint free shop rags and brake cleaner, scotch brite pads, sometimes a 1/4" angle air tool with a scotch brite on it to clean up a gasket surface or remove grunge. I don't recommend gasoline since its so highly flamable. has unpleasant odor and carsonogenics in it, and will leave an oily residue.

I use anti sieze on bolts to keep them from gauling, its cheap insurance at the next teardown.

Remember, go together "clean" so you don't have oil or fluid leaks. Take time, do not rush the job. When will you have time to re-do it?

Make absolutely sure your mating surfaces are clean from any leftover gasket residue.

Everything as stated above but you should use the scotchbrite pad to deglaze the inside of your cylinder, it is likely that it has a shiny surface by now and this isn't going to help oil retention on the surface of the cylinder.

The cylinder is easiest deglazed with a cylinder hone (Brush style is best but stone style will also work) but you have to be VERY careful with the stone type since it can remove a lot of material quite quickly and you do not want that to happen, so most recommend using a green scotchbrite pad to avoid removing too much material. All you need to do is get a fine crosshatch on the surface.

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