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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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guides are probably fine unless there's a ton of hours on it. yes you need the valve compressor tool. you may need the seats reground. valves may be fine.

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What are the service specs of the valves. the manual tells me valve head/stem O/D but is there service limit on the length of the valve? How can i test the head for leaks once its off?

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dont sweat it... measure your valve clearance and also figure out what size shim you have under the bucket. if you are within specs, i wouldn't worry about changing the valves yet. the only problems with valve guides i have run into are the honda CRF's exhaust valves. as for checking if the valve is leaking, with the head off pour some gas into the intake tract and observe from underneath if the valves are not "weeping" around the seams. i would only change the valve stem seals if they are letting oil pass or if im changing the valves. (the reason for this is that you can damage a valve stem seal pulling the old valve out, which can cut the seal)

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Thanks for the info, but I wont need the OLD seals once the valves are OUT so doesn't matter if they get cut.

Did you mean I could damage the NEW seals by putting the valves back IN.

I was told to change the valve stem seals whilst the head was off, but if its OK to leave the old ones in then that makes life a bit easier.

Just one other thing. What is the best thing to use to clean up the carbon from the head?

Thanks again

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i dont think we understand each other completely. if you pull the head and find that you have good valve clearance and an acceptable shim size under the bucket, then you do not need to replace the stem seals. and YES you can cut the new valve seals on install of the new (or old) valves...

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