Loose Exhaust Manifold Nuts

[Anthony S.]

During my engine rebuild, I installed new studs and brass nuts on my exhaust manifolds. I developed an exhaust leak about a month ago at about 800 miles after the rebuild.

I got a look under the car this week, and it turns out that 2 of the brass nuts on the passenger side, and one on the driver's side fell off (that explains the leak). All of the remaining nuts were loose.

My question is..........I know that the brass nuts do not require a lock washer, but how do I prevent these nuts from coming loose (I bought a new set) in the future.

Thanks,
Anthony

[Joseph K.]

Re: Loose Exhaust Manifold Nuts

Anthony,
I had the same problem after my rebuild of a 69 SB. The Brass nuts kept coming loose. I finally double nutted them to stop them from loosing up. I would be very interested in the answer to your question. Also to find out what the correct way it should be done.
Joe

[Joe L.]

Re: Loose Exhaust Manifold Nuts

During my engine rebuild, I installed new studs and brass nuts on my exhaust manifolds. I developed an exhaust leak about a month ago at about 800 miles after the rebuild.

I got a look under the car this week, and it turns out that 2 of the brass nuts on the passenger side, and one on the driver's side fell off (that explains the leak). All of the remaining nuts were loose.

My question is..........I know that the brass nuts do not require a lock washer, but how do I prevent these nuts from coming loose (I bought a new set) in the future.

Thanks,
Anthony

Anthony----


What you describe is a VERY common problem. Some pointers:

1) the brass nuts DO require a lock washer, although I don't really know how much good it does since lock washers are only marginally effective, at best. Nevertheless, it does require a lock washer;

2) the original nuts were a special, self-locking type nut. These work well but NOT when you want to remove them a few years down the road;

3) you will NEVER have a situation where the nuts don't loosen up if you use the stock-type donut gaskets. These compress and, as they do, the nuts will loosen. It doesn't matter what type of nut or lock washer you use---they'll loosen when the donuts compress. Instead, use sintered iron donut gaskets. These will seal very well, never blow out, and never compress. For 2" applications use GM #3731062; for 2-1/2" use GM #3767556.

[Joe L.]

Re: Loose Exhaust Manifold Nuts

Anthony,
I had the same problem after my rebuild of a 69 SB. The Brass nuts kept coming loose. I finally double nutted them to stop them from loosing up. I would be very interested in the answer to your question. Also to find out what the correct way it should be done.
Joe

Joe-----


Double nutting also works very well but only if one uses the standard thickness brass nuts. Very often, the long brass nuts are used for the exhaust studs in order to provide more wrenching surface (often a benefit when one tries to remove even brass nuts from exhaust studs). With these, there usually isn't enough stud length to double nut.

Regardless, though, whether one uses double nuts or anything else I previously mentioned, the nuts will become loose when the packing compresses. The sintered iron rings eliminate this problem once-and-for-all.

[Joseph K.]

Re: Loose Exhaust Manifold Nuts

Thanks guys that was very help full.

Joe

[Stuart F.]

Re: Loose Exhaust Manifold Nuts

I guess you just have to wait for the studs to rust up some to keep the nuts from backing off. You do have steel studs, don't you? I don't recall if you said whether or not you had SS studs. Have to go back and check.

Stu Fox

[Joe L.]

Re: Loose Exhaust Manifold Nuts

I guess you just have to wait for the studs to rust up some to keep the nuts from backing off. You do have steel studs, don't you? I don't recall if you said whether or not you had SS studs. Have to go back and check.

Stu Fox

Stu----


Personally, I would NEVER use anything but stainless steel exhaust manifold studs. I wish GM would have done that, too. A lot fewer manifolds would have "died" due to broken ears caused by trying to remove frozen and corrosion-deteriorated studs.

[Stuart F.]

Re: Loose Exhaust Manifold Nuts

Joe;

I whole heartedly agree, but we haven't heard from Anthony about this yet. I recognized that potential problem long ago and, well, I'm on my third exhaust system with no busted manifolds (back in the day we could only get plain carbon steel pipes and they didn't last too long). My present aluminized system has been on since 1992 and still looks like new.

In a recent thread on another subject, which included "change out of the heat riser butterfly valve for an F.I. spacer", I expressed my concern for dealing with the R.H. manifold and pipes to do the job on a 63 (what with that super hanger used on them compared with all other C-2's). One respondent posted that they had changed the studs out for bolts (not judging cool) to make future changes easier due to not having to deal with the hanger. Interesting.

I don't know why my brass nuts have never shown any signs of becoming loose. In fact, I just sprayed them w/WD-40 last oil change in prep for replacing my valve w/ a spacer. They look nice and clean and tight, about 1/2" thick w/ an equal amount of threads still showing on the studs. I will check my stock of donuts to make sure they are the metallic kind. That's a good point too.

Stu Fox

[Jim T.]

Re: Loose Exhaust Manifold Nuts

Joe where do you get your stainless steel studs for the exhaust manifolds?

[Anthony S.]

Re: Loose Exhaust Manifold Nuts

Hey Stuart, I have the steel studs, not stainless steel.

Joe, three Chevy dealers near me & my local parts store are out of stock on the sintered donuts, I'll have the dealer near me order them. They come in bags of 5 (?) so I'll have some extras if anyone needs 'em.

As for the nuts, I found a thread in the archives with a tip from John Hinkley on the correct "crimp" type nuts from Paragon (6498K) which I just ordered along with some other stuff.

Hopefully the combination of the sintered donuts & crimp nuts will do the trick. I'll be checking the nuts after a couple of hundred miles.

Unfortunately it's getting cold , so those miles may not come for a while.

Thanks guys,
Anthony

[Joe L.]

Re: Loose Exhaust Manifold Nuts

Joe where do you get your stainless steel studs for the exhaust manifolds?

Jim-----

Dr. Rebuild or Paragon have them. Just like the stock configuration except in stainless steel.

[Anthony S.]

Re: Loose Exhaust Manifold Nuts

One last question.............Do the crimp nuts from Paragon require lock washers?

[Joe L.]

Re: Loose Exhaust Manifold Nuts

One last question.............Do the crimp nuts from Paragon require lock washers?

Anthony-----


No, they don't. They are a self-locking-type nut. Lock washers were never used by GM in conjunction with self-locking-type nuts.

[Stuart F.]

Re: Loose Exhaust Manifold Nuts

Why not employ Pal Nuts and take them off for judging?

Stu Fox

[Chuck G.]

Re: Loose Exhaust Manifold Nuts

Here's a pic of the "top loc" nuts currently sold for exhaust applications. These are slightly different from the originals

They're sort of oval in shape internally, and provide an interference fit, sort of like the rocker arm adjusting nuts.

Chuck