427 Engine Intake Seal

[Herbert L.]

I have rebuilt my 1969 427 L36 engine and am concerned with the fitment of the 3947801 intake against the block at the front edge. There appears to be insufficient compression of the rubber seal along the front of the block where the manifold seals. The gap, after the bolts are torqued, is 0.100" to 0.125" which I feel is too much for the rubber seal to bridge - although I cannot detect an actual gap. The fitment at the rear is a little better. I used the GM assembly adhesive but still don't feel this looks right. I have pictures if that helps.

Anyone have experience with this? Comments or suggestions?

Herb

[John M.]

Re: 427 Engine Intake Seal

Herb,
Did you have the heads milled? How much? This will increase the gap to some extent if the intake side or the manifold isn't machined also. The silicone RTV does a good job of sealing this gap. Hopefully, your intake maifold is sealed to the heads.

[Craig S.]

Re: 427 Engine Intake Seal

Herb - I agree with John - head milling will raise the intake. I can be machined down to match, but I hate to do that. Usually it is best to keep the original dimensions and make up for the factory 0.022" steel shim head gaskets with a set of Felpro composition gaskets that have a 0.038" or so compressed thinckiness. What gaskets are you using on the head to block? .........Craig

[Herbert L.]

Re: 427 Engine Intake Seal

Craig, thanks for the comments. I'm having trouble accepting the head milling argument, however. It seems to me that the geometry of the block, heads and manifold are such that simply planing material from the head combustion surface does not influence the intake manifold sealing plane nor it's vertical relation to the block. Some other goofy thing must be present.

The head and intake gaskets are generic from NAPA. I do agree with you that it would be best not to mill the intake. Perhaps the best approach is to seal the manifold to block joint with RTV or other(?).

[Clem Z.]

Re: 427 Engine Intake Seal

set the intake on the engine without any intake gaskets and see what shows up. check the gaps by moving it side to side to see if anything looks out of wack.since BBC chevy heads have a 90 degree angle from the head gasket surface to the intake gasket surface cutting the heads only drops the ports and bolt hole down and this can be corrected by just slotting the intake manifold bolt hoes.