Inliners International Forums General Discussion Hi Performance Reground Cam and Changes to Valve Train Geometry

Unless the manufacturer says otherwise, the usual rule of "how many exposed threads" for best pushrod length is no more than 1-1/2 turns out.
Reason: the longer exposed adjuster thread changes the angle of the pushrod side lever and reduces the effective rocker ratio (plus minimal change to the rocker geometry).
Are you using the original GMC rockers? If so which ones? I've seen some stamped (early) rockers on running race engines that were beyond their "sale" date (twisted, loose adjuster) but no idea what RPM, cam or valve spring did that.
The only great GMC rockers are custom made at $$$, no modest cost aftermarket ever AFAIK. The problem: they're TOO LONG between PR and stem.