[Walt Fricke]

I can confirm that the lash increases with temperature, as I once replaced a broken rocker on a hot engine at the track. To set its lash I measured a couple of nearby, hot, valves, and used a thicker feeler gauge to do the reset on the new one.

Paul - I'm not sure I buy seat time as the reason for the factory lash. Cam shape has more to do with that, does it not? And the amount of time a valve is closed varies widely with cam specs. Certainly a standard is needed to set cam timing.

Best rationale I have heard deals with ambient temperature: set valves at room temperature, then take car to Alaska or Finland (or Gunnison, Colorado) in winter. On start-up of frosty car, rocker might not get off the base circle at 30 below F if you fudged the clearance to get more performance by keeping valves open a little longer.

VWs used 0.006," but there was the expansion of a longish aluminum push rod to deal with there. The Elgin 315 cams in my 2.7 race motor are set at 0.008" lash. Why Dema felt that was needed (his other cams have more normal lash recommendations) I don't know, though I faithfully follow it. Certainly can't have had anything to do with worries about sub-zero temperatures. Maybe the shape of the cam ramp.

I think it is easy to get the lash correct within 0.001" using the traditional "how hard is it to slide the feeler through" method. But I've never seen a tolerance given either. Maybe they believed mechanics would come close enough - within 0.0005" or so.

Walt