Originally Posted by Foot dragger
8 years on one set of valves,dang the guys who race em around here go a rebuild a year,then the head is ruined at some point along with the crank,then the cases can crack on a hard ridden race 450 or 250.
I know, reading Thumpertalk about those CRF horror stories used to scare me! But the valves stayed in spec and it was 8 years till I ran out of thinner intake valve shims. The clutch plates lasted 8 years too, with a Rekluse autoclutch. Now I did only race Supermoto one of those years, the rest was trail riding and some track days. I really think the combo of leaded fuel and not hitting the rev limiter was the secret.