How to Measure Preload and Determine Pushrod Length:
- Adjust the lifter to the base circle of the cam for the valve you want to measure (see below)
- Using a pushrod that you know the length of (stock is a good starting spot, it is 7.400”), tighten the rocker arm bolt down to zero lash. Do this with your fingers, when the slack is gone you have reached zero lash.
- Using a torque wrench set at 22 lb/ft, torque the rocker bolt while counting the number of turns until it is torqued. One full turn with a stock rocker arm bolt is about .047” preload.
- You are looking for 1 ¼ to 1 ¾ turns with OEM GM Lifters. If you come up with LESS than 1 ¼, you will need a LONGER pushrod to get into spec. If you come up with MORE than 1 ¾, you will need a SHORTER pushrod to get into spec.
How to Get the Lifter to the Base Circle of the Cam Using the Exhaust Valve Opening, Intake Closing Method:
As the exhaust valve opens, the intake lifter will be on the base circle of the cam; check the preload on that cylinder’s intake valve.
As the intake valve closes the exhaust lifter will be on the base circle of the cam; check the preload on that cylinder’s exhaust valve.
