Valve Lash

[William P.]

Hello all:

I recently purchased a 71 LT-1 and need to set the valve lash clearances. Does anyone know what the factory specifications are for this?

Thanks in Advance
Bill Pearson
40831
Red/Red 62
71 LT-1

[Joe L.]

Re: Valve Lash

William-----

Intake---.020" (hot)

Exhaust---.025" (hot)

The information provided in some references, including Chevrolet Service Manuals, calls for .030" on both intake and exhaust. This is incorrect.

[Duke W.]

Re: Valve Lash

I recommend .021"/.026" based on the ramp heights of .016"/.020" and the actual 1.37:1 rocker ratio at the lash point.

GM recommends .024"/.030", but that's based on the "advertised" rocker ratio of 1.5:1. The .030"/.030" recommendation in some service manuals is the GM recommended clearance for the old 30-30 cam based on a 1.5:1 rocker ratio, so it's wrong on both counts.

The spec sheet that is included with Speed Pro LT-1 cam clones says .020"/.025", which is okay, given that base circle runout is typically a thou.

The clearance tends to loosen with mileage accumulation.

Duke