they make little torque as it is... why would you want to make the cam feel bigger by tightening the lash??? LOL
A
Because with stock stamped rockers the .030" lash puts the lifter off the clearance ramp, onto the acceleration flank of the cam lobe before the rocker contacts the valve stem; beats up the valvetrain. From the article:
<<The factory 0.030-inch/0.030-inch (intake/exhaust) clearances are derived from multiplying the 0.020-inch maximum height of the clearance ramp above the base circle by the theoretical max lift ratio of 1.5. However, the actual as-measured lift ratio for the stamped OEM rocker arm at the lash points is actually about 1.37:1 (not the design ratio of 1.5:1, which is a theoretical max lift measurement, or the actual as-measured max lift with factory stamped rocker arms, which is about 1.44:1). The desired clearances in this procedure are therefore derived by "factoring" the OEM recommended clearances by the ratio 1.37/1.5 to compensate for the actual as-measured rocker arm ratio of 1.37 at the lash point. That number is then rounded down slightly to result in the cold clearance number. The clearance ramp, which is exactly 0.020-inch high on the lobe, is all taken up at 1.37 x 0.020 = 0.0274-inch clearance. Rounding down yields the desired 30-30 cam clearances of 0.026 inch/0.026 inch for this cold procedure.
Using the 0.030-inch clearance with the valve closed is too loose - the ramp ends/begins before the 0.030-inch clearance is taken up, resulting in the valve being lifted off and returned to the seat at greater than ramp velocity. This will contribute to valve seat recession, and can cause valve bounce at the seats at high revs - it will also be noisy.>>
