[DeTomaso] Rocker geometry problem solved

[JDeRyke at aol.com]

Good diagnostic job, Doug, and some neat machining! To all- because the 
direction of the pushrod relative to the rocker changes during the valve cycle, 
more clearance should be cut at the bottom of the rocker than at the top. 
Now, paint the clearance slot you cut with Dykem-blue or some brittle lacquer 
and run the engine hard, then check a couple of rockers to see if you cut 
enough clearance everywhere. Rub-marks will show where you need a little more 
hand-contouring. This will be a worse problem on most aluminum roller 
rockers if you run 3/8" or larger pushrods- which are recommended for high rpm 
use. The cut area on most rockers is only significant if you run 
locomotive-strength valve springs and/or over 7000 rpms. Then, stronger 
cast-stainless-steel roller rockers are indicated.

A second thing that sometimes bites guys is, the roller rocker's pivot 
shaft must be dropped onto the rocker stud with the round side down. This puts 
the machined flat spot on the pivot shaft upward where the rocker nut can 
bear solidly against it. Roller rockers can be adjusted to work either way but 
the lock nut won't have enough surface to bear against if the round side is 
up, and your valve clearances will constantly change- sometimes in only 50 
miles! Cheers- J Deryke