I have checked my valves for the first time around 59hrs. My exaust valves are at the low end of the spec. @.20mm and ,23mm which is in spec.Tolerence of .20mm - .25mm. But my intakes are .05mm and .08mm this is out of spec. The tolerence range is .10mm - .15mm. I know the valve's and seats wear before the lifters and shims, so were always going to be chasing the ever shrinking tollerences. I'm not as much concerened about the intakes being on the low end of the out of spec as I am about the exaust. I have always (on other engines) run my intakes tight with no problem. I have talked to 2 moto/jet mechanics and they both said let it go and check it in 20hrs. Then if its changed, go ahead and adjust w/shims. They both have built several 250's and been very successful but never the 450. Anyone got any advise..The enging runs great..