Valve Spring installed height_C2

[Steve D.]

I have 462 heads. The OE spring installed height spec is 1.66", and the spec for the spring I'm going to use (3911068)is 1.70" I am installing an LT-1 cam with lift spec of .435 Int and .455 Exh.

I used a spring height mic to measure installed height at each valve seat and got a range from 1.636" to 1.70". I assume that I need to have the out-of-spec seats machined to allow the specified installed height?

Steve

[Duke W.]

Re: Valve Spring installed height_C2

I'm not aware that GM ever published a tolerance range for installed height. Maybe later CSMs or COMs have a range, but there in none in the '63 Corvette shop manual. The biggest concern is spring bind at full lift. I don't think that will be the case, but I recommend you measure coil clearance at full lift on the springs with the lowest installed height, particularly if they are on the exhaust side. If there is no spring bind, I don't think machining the head to increase installed height is necessary. Actual valve lift of the LT-1 cam is more like .423"./.441" when you take into account actual rocker arm ratio.

If you checked spring force before you installed them, place the "weakest" on the valves with the lowest installed height.

Duke