Need fast advice on leaking pipe plugs (exhaust manifolds)

[mkronmal]

Just replaced all 4 exhaust manifolds on two engines. Crusader 350XLs.

The outboard side manifolds on both engines have pipe plugs leaking. On both of them the forward bottom facing ones are worst (this stream from sides of plug, really looks like its just passing the threads).

I used Perfect Seal (av gasket compound) on all pipe plugs. I also tried tightening them up and they still leak. Pulled out and replaced with a new plug with PS on it (although there was still coolant wetness in the hole) and replaced. Still leaks.

I've got recommendations on trying:
1. Teflon Tape
2. Ultra Black
3. Shellac

Any other suggestions, or something I may have missed?

Thanks!

[Randygh]

I used a copper based antiseize compound on my manifold plugs, but I don't think they would have leaked even if I didn't use the antiseize compound. I have to drain my manifolds and heat exchange unit because they will freeze here in Wenatchee during winter. I used the antiseize so they won't rust as bad. Teflon tape would probably stop the leakage, but I don't know if it will hold up to salt water circulating through the manifold. Gene will know what is best to use.

[heymagic]

Obviously there is a problem of some sort with the casting or threading in the manifold. I've never run across this before. RTV may cure it but has to be applied to a clean dry surface to be sure. Clean out the water, dry as best as possible, give area a good shot of brake kleen and dry again. Then use RTV and let set overnight before running. Your first approach with the AV gasket goop should have worked. Gene

[mkronmal]

Thanks Gene.

I was thinking about trying the teflon paste approach tonight, as I can test it right away. If that fails, I'm going to go with the ultra black and let it dry for a couple of days. Since I'm supposed to leave on the 3rd, I'm getting nervous...

[heymagic]

If the RTV could set for a couple hours it should be fine. We've used it on differential covers and transmission pans and filled almost immediately. Are you using steel or brass pipe plugs? A brass plug with a square head would be the best candidate for sealing . Gene

[mkronmal]

Steel plugs that came with manifolds. Sierra (Osco) manifolds. I reinstalled the plugs with teflon paste last night and I'll see how it goes this evening. If it doesn't work, I'll go with the RTV. Just need to get the opening nice and dry first.

Thanks

[mkronmal]

And the winner is....

Teflon Tape left over from my propane system install. The thick, good kind. Av gasket, PTFE paste, both failed.

Thanks for the help!

[Webjammin]

Be careful with teflon tape in this application. It could make your problem worse.

There is a potential of cracking the cast iron by by over tightening the steel plugs with too much tape on it. More may not be better in this case.

Remeber pipe threads are an inteference fit.

[Randygh]

What is an interefence fit?

[mkronmal]

I did not overtighten at all. The cracking of manifolds seems to come from people who use 2 foot breaker bars to flush the pipe plugs with the manifolds. I actually have the plugs in between 1/3 and 3/4 of the way and knock on teak, its holding.

[heymagic]

Randy, pipe threads are tapered. The further in the hole the smaller the diameter. The plug is forced into the side of the hole causing the seal..interference fit. Gnerally some sealer/goop will fill any minor imperfections. Teflon tape can lubricate the threads enough to allow over tightening of the fitting...the manifold is forced to expand and cracks outward from the hole.

[mkronmal]

I would also think that the cracking would happen with or without the tape (or other compound for that matter) if you torque that puppy down.

And besides, if the coolant can steam through, there must be some space left. :)

[Webjammin]

Maybe the proper term to use would be Tapered therefore there will be interference.

Dry seal pipe threads are tapered and the crest of the pipe plug thread will actually crush into the root of the hole thread, and for instance a
3/4 pipe plug will require 9/16 min engagement to provide a liquid tight joint.