Re-installing exhaust manifold

[1973 Ericson]

I pulled the manifold off to have it hot tanked and repainted. Part of an ongoing war on corrosion.

When I got the manifold back from the machine shop. It looked great... nice clean passages primed ready to paint. A couple of problems I see however...

The threads on the aft cooling water fitting have deteriorated badly (the deteriorated threads werent visible with the build up of gunk). One of the previous owners must have used a fitting of the wrong material which caused the manifold to corrode away in that area. There are probably 2 to 3 good threads left but I cant get the fitting to seal with regular teflon pipe dope.

The bottom of the raw water passage inside the manifold still has a thick layer of hard gunk build up. When I remove the drain plug at the aft end of the manifold the hole is blocked. I carefully scraped out a bit of the gunk figuring I would break through into the water passage but never could reach the water passage.

1. Was the cooling water fitting a tapered pipe thread? What size?

2. What should I use to seal the threads as I reinstall the new brass fitting in the deteriorated hole? (Cold Weld ?)

3. When you hot tank the manifold is it typical for a layer of hardened gunk to remain in the bottom of the water passage or should it come back completely gunk free?

4. When I reinstall the manifold on the block do you install the gasket dry or does it need to have some sealer on it? If so what type is recommended?


Thank you for the help

Tug
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Chrysler Akino

[Don Moyer]

Tug,

No offense to the rest of our good Forum Fraternity, but I thought I'd better take a stab at your questions myself, having been down this pot-holed road myself numerous times.

1. Was the cooling water fitting a tapered pipe thread? What size?

The water outlet of the manifold is 1/2" tapered pipe thread. In worst cases, you can grind off the end of a 1/2" tapered pipe tap and continue chasing the threads almost to the upper end of the tap if necessary to get another thread or two of good metal in the manifold. In worst-worst cases, if the threads end up being a bit sloppy, install a 1/2" by 3/8" brass reducer bushing and seal it using JB Weld between the outside of the bushing and the manifold. Then use a 3/8" by 1/2" hose barb to connect your water hose.

In worst-worst-worst cases, drill the hole out to 29/32" and retap the hole to 3/4" pipe threads and install a brass 3/4" by 1/2" reducer bushing. In this case, you may want to take the manifold back to your local machine shop. They should be willing to take you to 3/4" pipe threads for another $25 or so. The 3/4" tap could cost almost that much.

2. What should I use to seal the threads as I reinstall the new brass fitting in the deteriorated hole? (Cold Weld?)

See above. Cold Weld would do, but JB Weld is probably a bit stronger in this high heat environment.

3. When you hot tank the manifold is it typical for a layer of hardened gunk to remain in the bottom of the water passage or should it come back completely gunk free?

Yes, it is very common for a build up of crud to remain. Removing the freeze out plugs is standard in our rebuilding operation, which helps a bit to get more of the crud removed, but it's no panacea.

4. When I reinstall the manifold on the block do you install the gasket dry or does it need to have some sealer on it? If so what type is recommended?

In cases where the surface of the block and manifold are both in good condition, we like to install the gasket dry. If there is deep pitting on either surface (particularly in the surface of the block) we apply a good layer of JB Weld, then the gasket, then Permatex aviation brand between the outside of the gasket and the manifold. We like to see a bit of the JB Weld ooze out as we torque the manifold nuts to 25 foot-pounds. Afterward, you can clean up the JB Weld and Permatex.

Don

[1973 Ericson]

Thanks Don...

I will re-assemble the manifold according to your suggestions and report back on the results.

Thanks for the valuable advice.

Tug
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weed vaporizers