Reply to "valve adjustment questions"

Some OEM manufacturers quote hot lash, others quote cold lash. The Boss 351 was quoted both ways by Ford, one in the owners manual, the other in the work shop manual. That can be confusing! However the manufacturers of aftermarket cams all quote "hot lash" as far as I know. Hot lash, i.e. when the engine is running, is a "real world" setting.

One thing that can be overlooked however, pay attention if the aftermarket cam grinder's lash clearance is specified at the lobe, push rod, or tappet. Lobe, push rod, or tappet lash must be multiplied by the rocker ratio if you plan to measure lash at the valve tip. It is quoted this way by some cam grinders because an aftermarket lobe may be used in an engine having 1.5:1 rockers, or in another engine having 1.8:1 rockers. The rocker ratio impacts the lash setting as measured at the valve tip. If its not stated that way, then assume the lash is quoted at the valve tip, and no multiplication is required. Most of the time hot lash measured at the valve tip will be in the 0.020" to 0.030" range, but some cam grinders offer aggressive race cam lobes that are "tight lash" lobes. Tight lash lobes will have a hot lash setting less than 0.020" (at the valve tip).

If the rocker arms are swapped for arms having a different ratio, the lash setting should usually be adjusted to reflect this change.

Even though its quoted "hot", the lash of any camshaft can be set cold too, using these guidelines:

(A) Iron block and iron heads: Cold lash = hot lash setting plus 0.002”
(B) Iron block and aluminum heads: Cold lash = hot lash setting minus 0.006”
(C) Aluminum block and aluminum heads: Cold lash = hot lash setting minus 0.012”