Maybe I don't know how to install an intake manifold correctly!

[Bill Crowell]

Recently I found that the reason my 440 was running so poorly and wouldn't smog was because I had an intake manifold leak. The smog tech discovered it by testing it with a smoke machine. I was the one who had installed the cast iron intake, so obviously I screwed up, but I'm not sure what I did wrong.

I also installed the intakes on my other Mopars (360 & 408 LAs), and now I'm wondering if I might have made the same mistake on my other engines.

So, two questions, please:

1. Has anybody got any suggestions for avoiding leaks when installing an intake? and
2. Any tricks for doing a smoke test on a carbureted engine? I've only seen it done on F.I. engines, and wondered if any different smoke test procedures apply to a carbureted one.

Thanks, guys!

 

[RustyRatRod]

What gaskets did you use?

 

[yellow rose]

What gaskets did you use?

This is the first thing that needs to be answered.

Don’t forget...we are working on 40-50 plus year old stuff. Most intake manifolds are flat after a few heat cycles. When they get that old, it’s worth it to get a surface on them to get them flat and straight.

 

[MoparMike1974]

Might not be your fault. If your using the old metal gaskets, thats likely your problem. Check the intake and head surface with a straight edge, might be warped. Lastly clean both surfaces real good and make sure no old gasket material is left. It only takes a small piece to cause a leak.

 

[rustycowll69]

I agree with previous posts. Sure, make sure the mating surfaces are straight, but you need a precision straight edge and fine feeler gauges for that.
Something I like to do if I'm assembling an engine, which I don't know the history of, is I bolt the intake to one head(no gasket) and use feelers to align it to the other head before I finally snug it down to first head. Then use your feelers, again, to make sure the gap between the other head and matching manifold surface has a consistent gap end to end and top to bottom. If one head has been surfaced more than the other, and/or been unevenly machined front to back or side to side, OR somebody has removed the locating pins for the heads/head gaskets to the block, OR the block decks are not square & parallel to crank centerline can generate an uneven gap that the intake & intake gasket can't seal. Does this make any sense to you?

 

[mbaird]

Use a set of the old six pack gaskets.
That should fill the gaps unless the angles are wrong due to head or block resurfacing .

 

[gdrill]

I was going to suggest potential resurfacing on parts as well.

But as usual, the FABO team has the answers!

 

[Cuda416]

It would also help to know "where" the leak was. For instance, it's pretty common to have one at the ends where the angle from heads and block intersect. Could be as simple as not enough sealer.