RE: Screaming Eagle Quick Install Pushrod Adjustment
The universal "magic" number for the tappet piston adjustment is .100 down from fully extended (piston against retaining ring). This will put the piston at approx. half travel in the tappet body. This varies with thread pitch of the pushrod adjuster and so the number of turns. On 24 pitch threads this equals approx. 2 1/2 turns. I.E., 2 1/2 turns will extend the pushrod approx. .100 inch (actually .1042). If you have unkown pushrods, you can simply count the number of turns it takes to make it .100 longer and this will be your pre-load adjustment turns when installed. Some builders will adjust them slightly longer (typ. about +.030-.060) to set the piston deeper in the tappet hoping to reduce tappet noise. We've not seen this work every time and when it does, I believe it is more a function of the piston positioned in a "fresh" area in the tappet bore. I have not heard the "3/8" travel number and even at half (3/16) this would translate into .1875 down on the tappet piston which could cause it to be bottomed holding the valve open.
When adjusting, make sure tappet is on the cam heal and, when done, make sure the pushrod spins freely (indicating the tappet has bled down) before rotating the motor. Use 2 1/2 turns with your pushrods.