For the hell of it I installed a set of comp cams 19001 roller rockers. This in a stock z/28 302. The 30/30 stock cam requires a 0.30 lash setting. However I read somewhere that roller rockers lash should not exceed 0.12? A little help here. Are you guys running factory cam lash settings? After I installed the rollers I set the lash to 0.26 cold. Haven't checked the setting after ran hot.
There has been quite a lot of discussion about the valve lash setting for the 302's cam, specifically when the original stamped rocker arms are used. The 0.030" lash value, done with the engine hot and running, has long been the spec as published in the Chevrolet Service Manual. There is a very extensive paper regarding this topic published elsewhere on the CRG website. In short, it recommends using a cold lash of 0.026" rather than a hot and running lash of 0.030" due to the specific contour of the stamped rocker arm pad that contacts the valve stem. Additionally, in my and others experience, there does not seem to be any noticeable difference in either performance or valve train noise when setting the lash cold vs. setting the lash after the engine has been warmed up and doing it statically. Attempting to lash the valves with the engine hot and running simply creates an oily mess that is difficult to clean up. No serious racers I know bother with the "hot and running" method.
When using aftermarket roller tipped rocker arms on my 302 "30-30" cam, I have always set the lash at the original 0.030" spec as these types of rocker arms have a more consistent ratio throughout the entire valve lift and the need to reduce the lash somewhat is no longer necessary. Other than the phenomenon of the OEM stamped rockers exhibiting a slightly variable ratio throughout the valve lift, which indicated a demonstrated need to reduce the lash from 0.030" to 0.026", there is never any reason to choose a different valve lash setting based on the design of the rocker arm being used. If one chooses to do this for their own reason, they should proceed with caution.
We used a Pair of Dial indicators on my Comp Roller Tip Mag SBC Rockers.
For every Hundred thou Lifter Lift we got 140 thou at the Tip of the Valve; So our Rockers REAL world ratio was 1.40
150/140= .9333333
93% of 030 = .028"
We set these rockers at 0.028" Cold.
I think this was the process JOHNZ called Factoring based on real lift results.
* My Biggest Lesson I could Convey would be do not Be fooled by the Mech Lifter Adjustment GM Service manual Photo (For example 1968 Service manual Page # 6-28 Fig. 4V - Valve Adjustment (Mechanical) REMOVE the Socket from the Rocker Nut when checking Lash with the Feeler gage. The Socket wall can contact the Rocker Arm & cause Binding and a FALSE sense of Drag & inaccurate Lash!
Seems like you could measure .020" lifter rise, then zero lash at that point without disturbing the engine. Back the engine off down to the base circle of the cam and measure the lash there. This would be the maximum cold lash setting for your stock "30-30" cam and what ever rocker arm you are running. The lash ramp is .020" high on those lobes.
The "30-30" cam lash ramp is so slow the difference between hot and cold would seem to be very small, but it would always be good to check it hot to see if it made a measurable difference. I have a car with an aftermarket cam that varies quite a bit from hot to cold but the lash ramps are much faster on that cam. Different profile demands it.