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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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I shoot carb cleaner in the intake and exhaust port and look to see if it bleeds back into combustion chamber.If they're bad it will blow right through but if they leek real slow your probably good to go.I do this once the head is off.

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You can change the valve stem seals without having to change the guides. You can check your guides yourself by taking the seal off and sliding the valve back in there and checking for slop. There shouldn't be much wiggle. It wont be tight...but it shouldn't rattle either. If the guides feel ok, just change out the seals and be done with it.

If you do need guides you need to make a decision on whether or not a new head is cheaper because when you do guides, you need to cut the valve seats too to guarantee concentricity in the valve pocket. But at that point, you've got a basically new head too in the end.

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