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Help With Top End Rebuild

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Hi guys,

I'v had my 08 RMZ250 now for a year now and as i don't know what "deep" maintenance has or hasn't been done on the bike, i'm going to rebuild the top end.

I'm happy changing piston, timing chain etc, but not 100% about removing valves.

I would like to put new valve seals in whilst its open.

I know just removing the valves are easy using a £30 tool, but will i need to re-seat and replace guides on them even if the valves are still good?

If so can i check if the valves are still good without removing them?

If It must be done (and out of interest) , how much will a shop charge for cleaning up the head, fitting guides, valves and re-seating valves?

Any help appreciated.

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Hello, the valves are easily removed without special tools if it´s a one time thing. If you run a race shop the proper tool is of course better.

You put the head on a shop rag on a flat surface (camshafts and buckets removed), and just push the top spring seat (spring retainer) down with a 13mm socket. It can be a 13mm T-handle or preferrably something a bit shorter.

If pushed quickly, the keepers will pop out. The same method can be used for assembly, just put some oil on the keepers and slowly push the spring and spring seat down and the keepers will fall right in.

You will probably not have to replace the valve seat. They can be recut. If nothing special has happened they can most likely be recut 3 times before you need new ones.

Recutting is not expensive. Probably around £30 for the 2 intake seats. £60 for all 4 of course.That is for just cutting the seats, assuming you get parts elsewhere and do the rest of the job yourself.

However, the if the valves still have clearance, there is no indication that they are worn. In that case you can just put the head back on and keep riding.

Valve seals and guides are usually not replaced unless the engine has very high hours or have a clear indication that something is wrong. Blue oil smoke would be an indication, but can also be a sign of worn piston rings or broken/improperly installed oil control rings.

The valve to guide clearance can be checked with an indicator dial. The valve stays in the head, and is pulled out just enough to get the dial´s tip to the stem.

Valverunout.jpg

Valve.jpg

A = valve

B spring seat

C oil seal

D coil spring

E spring retainer

F split keeper

G valve shim

H valve lifter (bucket)

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