Rocker Arm Geometry Question

[Marv D]

Originally Posted by 1968SWBBigBlock

Buy yourself a single solid lifter and use it when you check your pattern.
This eliminates the Hydro lift issue and gives a better reading.

Ditto, that is the only way to get meaningfull data from the witness across the valve stem tip.
If you really want to be 'dead on' adjust your resulting pushrod length by 1/64" (0.015) to simulate the depth of pudhrod sunk into the hydraulics with a 1/2 turn of preload.

But just keep in mind, Pushrods are available in 0.050" increments for a reasonable price (~$120) I mean Smith Bros will custom make any exact length you want,, for a price!!
But unless your plaing Cmp Eliminator and spinning 12,000 rpm a $800 set of pushrods is sheer foolishness.

A Stock length SBC pushrod is 7.80"
If your getting 7.75" and add 0.015 for preload depth,, well.... A set of stock length pushrods is probably going to be just fine. I wouldn't sweat it too much.

KUDOS to you for checking tho. You wouldn't believe how few people even give valve train geometry a second thought (and wonder why their valve guides are wearing so quickly or breaks pushrods, and springs and... )