replacing exhaust manifold/pipe nipple

does anyone have an idea about what might be best applied to the threads on the exhaust pipe nipple when tightening it into the manifold?-i was getting water in my oil due to worn out threads and did not realize it until recently-i replaced the manifold and have a new nipple-is pipe thread compound appropriate or something else to seal the threads against water-thanks-hank

I use industrial antisieze paste.

will that keep water out as well?

Pipe threads seal by metal-to-metal tightness between the male and female threads. Antisieze is routinely used with new threads to lubricate the joint so that it can be tightened well. New threads shouldn't allow leakage if tightened sufficiently. We assembled high pressure (1500 psi) chemical plants with antisieze in all the pipe joints. If you had leakage (with no pressure), then your threads were damaged. Thread "sealant" does the same thing, and may help with old, reused threads, but it's the metal seal that makes pipe threads "work".

I had a similar problem on my SMTA when I bought it, actually the next step of it, muffler rotted away and engine was stuck. Old pipe just wouldn't thread in well. I got a new pipe nipple but threads worn in manifold badly. I couldn't find a pipe tap that size so I got another short pipe nipple and made 4 cuts perpendicular to the threads with a hack saw. I threaded it into the manifold, turning it foreward and back to clean threads. I put a rag with some grease on it below the pipe in case some metal fell in there. You have to be some what careful as the tapered threaded pipe can exert great pressure on the manifold and you don't want to crack it. Anyway the second pipe nipple with cuts seemed to clean threads some. I used a long pipe wrench with cheater handle, but went foreward a bit then back a little. Finally got to where I could thread my pipe nipple for the muffler in sufficiently to hold. My manifold is really worn in the threads and the muffler on top puts a lot of leverage on it so it is tough to keep tight. I didn't use any sealant on it but suspect never sieze would be the way to go. Good luck but take it easy putting it together and use some patience so you don't crack the manifold. When I put the final nipple in the manifold again I used a long pipe wrench with cheater handle but I worked the nipple back and forth instead of just applying a lot of quick pressure to it.

I need to do this to my F504, the nipple is worn. One way to clean the threads out is to use a Dremel tool with the little cut-off wheel and run around the threads. This will get all the rust scale out and allow the pipe to screw in easily. Also recommend a good anti-sieze compound, Loctite and Permatex both make this.

I read the Dremel tip on this site some time back.

Good luck,
Charles

thanks for the help-my manifold is a new replacement as is the pipe nipple so i suspect the antiseize will do the trick-i also plan to keep the tractor under cover as much as i can so rain won't be much of an issue-it's been prety wet here this summer so i probably will get rained on but i think we'll be ok-thanks-hank

now that the manifold is set-i cranked her up and she runs just fine-any good ideas on how much to retorque the bolts on the manifold after warmup and cooldown?-i did them to 20 ft lbs when first tightened up-thanks