i got into my 1991 xr250l top end and found two stuck rings and the ex valves needed a bit of work. can these valves be resurfaced like most automotive valves if i can find someone who's machine will accept the small stems? i talked to a guy who is a yamaha mechanic (not so familer with honda) who stated all newer yamaha valves had a hard surface and could not be ground ar even lapped. don't know if this applies to honda or not.