Get ready to shake your head at me...

[bottobot]

How do you know the head needs guides? Did you measure the valve to guide clearance using the wobble test, and if so, what did you measure? New guides mandates machining the seats, so if you do that you should also cut the valves and skim the stem to assure you don't run out of shim sizes.

We did a wobble test and they wobbled like crazy. I hadn't considered skimming the stems, but the valves getting cut and the seats getting lapped are all on the order. You mean grinding down the top of the valve stem a little right? How much would you recommend?

[Nessism]

We did a wobble test and they wobbled like crazy. I hadn't considered skimming the stems, but the valves getting cut and the seats getting lapped are all on the order. You mean grinding down the top of the valve stem a little right? How much would you recommend?

Yes, face the valve stem to shorten the valve. How far you go depends on how deep the seats/valves get cut and what the current shim size is. For example, if your bike has 2.50 shims and you face the valves and machine new seats after replacing the guides (the seats must be cut if you replace the guides, lapping is no good) then you could easily be down to 2.40 afterwards, which doesn't leave you a whole lot of adjustment room for the future. In that instance I'd machine at least .005" off the valves, maybe more. Talk to your machinists and see what they say.

Oh, and be sure to measure the wobble using a good dial indicator. The only way to know for sure what the clear is is to measure.

[bottobot]

Yes, face the valve stem to shorten the valve. How far you go depends on how deep the seats/valves get cut and what the current shim size is. For example, if your bike has 2.50 shims and you face the valves and machine new seats after replacing the guides (the seats must be cut if you replace the guides, lapping is no good) then you could easily be down to 2.40 afterwards, which doesn't leave you a whole lot of adjustment room for the future. In that instance I'd machine at least .005" off the valves, maybe more. Talk to your machinists and see what they say.

Oh, and be sure to measure the wobble using a good dial indicator. The only way to know for sure what the clear is is to measure.

Whats the difference between cutting the seats and lapping the seats? I'm only familiar with lapping.

[2BRacing]

Lapping the seats with fine paste will ensure an even surface around the seat. However, when guides are replaced, the centreline of the new guide in relation to the old existing seat can change. Then a special cutter is used to remove more material than lapping will, to ensure a true centreline again.