MTFCA Forum

How does one go about repairing the exhaust manifold threads?

After searching the forum somewhat, here is what I am not talking about:
1) replacing the manifold
2) replacing the pack nut to get a better bite on the remaining threads
3) using exhaust sealant like "Permatex 80335 Muffler and Tailpipe Sealer"
4) adding a clamp or a ring in proximity of the nut

My threads are worn but I think they may still work but was wondering if there was some machining service or process available.
I'm also not sure if JB weld would work in this application or if anyone has tried it. I'm thinking that once the manifold heats up and expands that the makeshift threads would be lost.
Thanks

3/8-24 helicoil

I think he is talking about the threads on the manifold. I think you covered all the suggested fixes and unless this is an early type with the slide in pipe, would be looking at a lot of time, money and effort. Then come to find out it's warped.

another way ,cut off the old threaded part,then mach a new part out of steel then brase it on,i have done it, works fine.charley

with a half round file, you can clean up damaged thread easely

If time, money, and machinery were not limited... you could weld up the threaded portion, jig it up in a CNC mill, then mill the major diameter and threadmill to fit! Sounds easy right...!?!? You may want to consider saving this much effort for something a bit less... “readily available”

If the manifold isn’t warped I would try to clean the threads up with a small file. Other than that buying a new repo manifold might be the way to go. It will last you from now on or as long as you have your car.
They are well made and worth the money. A new nut with sharp threads will really help also.

This really has no bearing on the OP's post....just something I did to my first T back in the seventies. There were no reproduction manifolds back then, so I cut two matching flanges from 1/4" plate steel. One flange was split with a hacksaw, then welded back together behind the threaded section of the manifold....not welded TO the manifold. After the install, that flange could be rotated easily. The other flange was slid up the tail pipe until it hit the swaged section, and the two flanges were bolted together......BUT with springs under the bolt heads to allow movement.

I drove the car that way for at least three years with no exhaust leakage or problems. We have it good these days, with so many repro parts offered!

Oh, by the way, a special "thread file" is available at most big auto parts stores. It consists of a square file with teeth on each face that will re-cut many different threads.

New manifolds are not that expensive.

I fixed my manifold with a credit card.

In your case if you’re absolutely married to what you have, wasn’t there a run of wrong size repop exhaust nuts made? If they were a little undersize maybe somebody has one they can send you. Just keep reducing (and sharpening up) your manifold threads until it fits.

Wrap some 28 ga. copper wire on the first 4-5 threads up near the beginning of the threads as though you were using pipe tape. That will allow the (good) nut to get a better grip. Alternatively, if you have an old broken appliance like an iron or curling iron, you can strip the outer covering of the cord, remove the wires, and strip off the asbestos wire insulation. Wrap that around the threads and it will not only tighten the nut but help seal any leaks.

Sometimes, yes you can used a file or thread chaser but sometimes by time you clean up and reform the valleys, the tops are worn or burnt down past the point where even a new nut will only go so far and as it gets tight, jumps back and will not hold. The point I am trying to make is, you can make new valleys but you can't replace the tops so the outer diameter is now smaller then needed to get full grip on the the nut. Cleaning a bolt or nut that has a few bad threads is one thing, most of the time they are just bugged up, trying to replace worn down or missing threads is another.

I really like reading about these options. Some of the thread is completely gone but the pack nut is in good shape. There was no noticeable manifold warp when I bolted it to the engine.
I kinda like Charlie's suggestion of brazing a new thread piece in place but have a question: Is the pipe thread 1-7/8" x 16tpi?
Thanks,

I definitely agree with Erik...If your time and temperment have any value at all, this may be the best money you'll ever spend on your T: https://www.modeltford.com/item/3060B.aspx

A die in that huge size will cost more then a new manifold. Unless you can find and borrow a tap, replacing the manifold is probably your best bet.

It is not pipe thread it is straight thread.

Steve & others,
So, that means that perhaps ya'll may have some exhaust manifolds that did not survive straightening or some that are too far gone to even try to straighten up.
Some of you have already figured out where I am going with this.
I may be interested in a cut off section of just the good threads.

When I purchased my 23 Roadster, it had a large pipe union brazed on the manifold and pipe. Any port in a storm. First things that I replaced even though they worked.

Before I went with much labor, I would chase the threads and then wrap a narrow strip of aluminum foil over threads to make up for worn peaks and start the nut. If that doesn't work, I (like some others have already suggested) would purchase a new manifold.

I just couldn't help myself - this is how stupid I was about this. I bought not one, but two used original Ford stamped exhaust manifolds off Ebay that BOTH claimed to be NOT warped with pics of the pack nut end seeming to look okay, just because I like being original and that Ford stamp. Yes you know the ending, BOTH were warped, pack nut threads worn too much, so nothing but scrap metal. I bought a new one from Lang's and although it doesn't have Ford on it, it doesn't leak at all...

Varmet,

I scanned down al the threads and no one offered this suggestion!

Here's what I did and it has worked fine. I had the same problem the threads were worn and a brand new nut would tighten and then slip.

I took the new nut and cut one side of it. I found a Quality S/S worm drive hose clamp and formed it to match the outside of the nut. After carefully starting the threads so as to not cross thread them I tightened up the hose clamp around the nut squeezing it a bit on the manifold threads. After more tightening and getting a good seal for the exhaust pipe I tightened down the hose clamp as much as possible and again after the heating and cooling the same sequence. Has never been a problem since.

I do know of club member who wrapped his nut with one of exhaust epoxy type products to seal off any leaks and has good success. Not sure how he'll get it off...

I have a used exhaust manifold and a new brass nut. I can put the nut on about 1/3 of the way by hand before it gets to tight to turn. Is this normal? OK? bad news? a good start?

I have gone over the threads with my thread file(chaser) and they look ok.

I have just fitted a repro manifold for a customer. He ordered one and they sent TWO! It was a good thing they did. The finish on both was rubbish.
I rejected one because the no 4 port was very thin at the bottom. The part was misaligned before machining, and the ports were all at the low side if the cast holes. The second one was better, but the underside of the thread was interupted by a low section right across the thread. It will hold, but the quality control leaves a lot to be desired.

I can understand the reluctance to use a new manifold. They do not look like an original. There are casting differences and there is much fettling to do to remove casting lines to get them into shape. Straightening an otherwise good original all of a sudden becomes a good way to go. But, if none of this bothers you, a new one does fit easily.

Allan from down under.

My manifold is straight and good. My only question (at the moment) is fitting the nut. Is hand tightening the nut the first third of the way normal? Or do I need to do something?

Find the best old nut you have. Cut about 1/4 inch out of it with a Dremel or hacksaw with a taper toward the leading edge of the cut. With the Dremel, cut several grooves across the threads at an angle, again with the leading edge in the direction it will be turning when you thread it on. Put a hose clamp on it and tighten it up as tight as you can get it. Slop a bunch of Kroil on the threads and you have a die. Turn it with a pipe wrench or something. You will be amazed at how the brass nut threads will clean up the cast iron rust and rethread it.

While the Kroil is soaking, tighten up the hose clamp again, go in and fire up the computer and click on the Chaffins site.

Order a new manifold and nut.

Or go back out and cut about 1/16 of an inch out of another nut, braze the cut after you clamp it on the pipe and it will hold.

The new reproduction exhaust manifolds are well made. They are a reproduction item that’s well worth the money.

What is the diameter of the exhaust manifold (what is the nut size?) and the thread size? 16 or 18?

1 7/8” x 16 for exhaust manifold thread.

I am surprised nobody has mentioned this. Some years back, a bunch of repro exhaust nuts were made that were slightly under-size. They typically only go on about a third of the way without a hassle. Perhaps that is what you have? I had one years ago, and used valve lapping compound to work in the fit. Slow, but it worked. Sometimes those under-size nuts are nice! They may hold onto a tired manifold that a properly sized one would be too loose.
These days, if you need a proper size one, they are not expensive. Call and talk to your supplier and make sure he sends one that fits a good standard manifold.
It IS also possible, to have a manifold that is messed up somehow. But that could only be determined by close examination. But the basic answer to your question, is, no, it is not supposed to be like that.

Google OTC 7402 Universal OusideThread Chaser. You can buy one for about $70.

The manifold I tried to use a file to straighten up the threads was so hard the file wouldn't touch it.

Thank you guys. I now believe I have the information I need to solve this problem.

This forum is a life saver, Jed