MRZ28HO

On Small Block Chevys, the rocker stud is a 3/8-24 threads per inch (GM OEM type, not aftermarket or Big Block 7/16"). GM recommends .020" to .060" preload on all hydraulic lifters from zero tension on the pushrod (actually they say "from zero lash, but it's clearer this way). So you could either use a dial (depth) gauge to come up with the preload or 1/2 to 1-1/2 turns. Why 1/2 to 1-1/2 turns? Because if we look at the threads (24 Threads Per Inch) we can calculate that .020" is 1/2 a turn and .060" is 1-1/2 turns. The prefered lash or preload should be 1 full turn or .0416".

Definitions:
Preload = the amount of the hydraulic lifter cup/seat is pushed in with the push rod.
Zero Tension = Using your ring finger and thumb, you should be able to spin the pushrod freely. Once you start to feel a bit of drag, you are starting to preload the lifter. Zero tension is before this occurs.

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George P. Lara
1984 Z28 High Output
Proud Member of SCFB
V6 T5 For Sale