1939 manifold leaks

[Pete Phillips]

I bit the bullet and spent $390 for a new manifold valve body on this '39 Roadmaster last week. Installed it yesterday after wire-brushing and cleaning the old manifold gaskets off of the engine and the intake & exhaust manifold surfaces where they mount. First I laid the manifolds on their side on the floor, using the flat floor to simulate the side of the engine, to line up the intake & exhaust manifold ports in a straight line. Then, I tightened down the bolts on the manifold valve body and the bolts that hold it to the center portion of the exhaust manifold. I used new manifold gaskets against the engine, and installed the manifold assembly to the engine. I have tightened and re-tightened the bolts that hold the manifold assembly to the side of the engine, but I still have very loud gaps at the center portion of the exhaust manifold (and probably at the intake as well, since the car doesn't idle now, and coughs and spits at low engine speeds, so that's probably a vacuum leak at the intake).

I cannot tighten the manifold bolts any more. Does anyone have some suggestions?

Pete Phillips, BCA #7338

[wmsue]

Are the intake and exhaust ports indeed in a perfectly straight line or are one set of ports a bit higher or lower than the other? I don't know....just asking.

I have heard of using 2 gaskets and copper spray Permatex to get a good seal in this type of setup.

Bill

[Terry Wiegand]

Pete, from what you have described, it sounds like you are going to have to have the manifolds machined to flatten them out. You might want to visit with your local machine shop and ask about their capabilities. The manifolding on a straight eight will require some table travel.

Terry Wiegand

South Hutchinson, Kansas

[DonMicheletti]

Check the height of the "ears" that the clamp washers bear on. If they arent exactly the same height, you wont be able to get the manifolds to clamp properly. I have seen intake and exhaust manifolds that were machined separately and the "ears" not be the same height. Since you say you have a new part, that may be the cause of the problem.

This can easily happen today since shops have probably never seen a big in line engine. On a "V" engine, it doesnt matter.

[1939_Buick]

Do you have the Pilot ring for the exhaust to head?

The 3 piece exhaust on the 320ci is much harder to seal than the 248

Some other threads on manifold but most(all?) are for the 248ci engine.

Straight 8 exhaust manifold gasket leak[47super]

Manifold gaskets Post 2 is good

Straight 8 Exhaust Manifold

Edited May 25, 2014 by 1939_buick (see edit history)

[Pete Phillips]

Yes, I have the pilot ring installed. I like Bill's suggestion of a second layer of gaskets, because the bolts seem to have bottomed out, yet there is still a slight air gap between the center section exhaust manifold and the engine. If that doesnt' work, I will remove everything and get it resurfaced, as suggested. Thanks for the suggestions. Will report back when I get some time to continue this work.

Pete

[Pete Phillips]

I finally had time to install a second layer of manifold gaskets today, between the intake/exhaust manifolds and the side of the engine. Happy to report that this fixed the problem, hooray and thanks to "wmsue" for that suggestion.

Pete