Is there documentation that reveals what the running lash is vs. the cold set lash on a CRF450R or similar engine? I have read on formula 1 engines the lash is set to zero when the engine is hot and when cooled the valves hang open and will not start. This process seems to be done before each race (setting and re-setting the lash). I would think the same situation applies to the dirt bike in terms of thermal expansion of the valves. I always thought the lash decreased just as an observation due to the valve train appearing more quiet when the motor is hot. The typical lash for the exhaust is .010"-.012" EXH and .005"-.007" INT. What I wanted was a lash that will yield the best power without burning a valve and a valve train that would be the best on the valves hitting the seats.