Rocker shaft shims

Mojack said

I've never used these before, but I'm building a budget BB for my Trailduster.
Rocker Shaft Shims
I've got a little too much lifter preload and I know the pros and cons. I just wanted to know if anybody could tell me if these shims are steel or alum, just curious.

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If the heads are otherwise stock, you may want to consider just getting a shorter pushrod. That would be the correct way to compensate for too much preload due to block and head machining. The shims mess with the factory engineered rocker geometry when using factory valvetrain components, not to mention, risk breaking the stands.