valve clearances

["Watry, Andrew (LNG-SFR)" <Andrew.Watry@domain.elided>]

About valve clearances, from what I've read in cam catalogs, the proper
clearance for a particular cam is also related to the ramp and lobe
design, which can vary between street and track cams pretty
significantly.  Cam makers discourage too much experimenting with
clearances. Too large a clearance means the cam contacts the tappet
farther up the lobe than intended (beyond the ramp) where the meeting
angle will be steep, and the valve is accelerated open harder and faster
than intended. The ramp smooths the transition between no contact and the
lobe.

My own experience has been on OHC non-rocker cams and rocker/pushrod cams
alike that clearances get looser when hot.

Andrew Watry
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