Roller Rockers Geometry

Mully 1 thread showing may or may not be enough. When I first put my rockers on that are like yours I had pushrods that were a little too long and when I put them on and adjusted them to load the lifter properly only about 1 thread was showing and it let the cup of the pushrod hit the rocker body at full lift. Pull your valve covers and turn the engine over to where one is at full lift and look at where the top of the pushrod cup is. If it hits the rocker body that may be your problem. On mine it made a clattering similiar to spark knock.

As Mully said I do have some extra pushrods if anybody wants one to make an adjustable pushrod out of. It's real easy. I just cut it in half taking about an extra 1/4" out of the middle and threaded it with a 5/16" fine thread die about 1" on both pieces then screwed on nuts all the way down then used a long coupler nut I found at ACE that serves as the coupler/adjuster. When you put it in you adjust it to the desired length and lock the nuts down against the long coupler nut and take it out and measure. Took me about 10 minutes to make it. If anybody wants one I have about 10 left so pm me and you can have one.