OK I have a question I have one of those Fords with the messed up exhaust manifold stud problems. So I replaced the manifolds with a set of Headman headers. Now this is where the problem comes in, they come from Summit with a "Y" to connect directly factory cat. The collector where the headers meet the y pipe WILL not stay tight it is one of those X3 bolt triangle shaped conecters. The bolts and nuts that came with the kit where cheepies so I replaced them with grade 8 nuts bolts and lock washers!!!!! They still come loose, I have hit them with and impact to tighten them and still they come loose???? Can anybody come up with something that will keep them tight ??? It's crazy you will be driving and you just end up with an exhaust leak at the conector!!!!!! The only thing I though of was to try and double nut them but it seems like a lot for a simple job?????

Were the old ones self-locking nuts? Not the kind with plastic inserts, but the kind where they are stamped so they are just a little out of round and ""grip" the stud?

Did you try plastic zipties Bob?

I'd try the double nut option. (always my favorite)

You might even try putting all-thread in there; or a long full-threaded bolt, and double nutting on both sides. You may get to a point where you pop the bolt head off. I've done that a few times; and you are then back to square one.

Another thought, are you loosening the bolts, or perhaps stretching them?
AND, I usually find that I can put a breaker bar and/or long pipe on a ratchet and go significantly tighter than any impact wrench. But that all depends on how good the impact wrench is, as well as your air pressure.

Have you tried using a compression spring with washers and nuts to keep a constant load on them and hopefully keep them from backing off or strecthing the bolts further by allowing some flex in the joint?

I had thought about that

i never use washers on exhaust systems,,that would be the first part to rot off and end up coming loose..i always just use a standard bolt with a hansen lock nut..go to your local ace hardware and look for a nut with the washer molded into it,on the bottom of the nut theirs grooves stamped into it that will dig into the metal and will lock it solid..the factory y pipe probably had studs,if this is the case you may want to tsck the head of the bolts with a welder to keep them from turning..

OK I did the double nut deal and used a lock-nut as the second nut so lets see what that does???

P.S. I talked to the ARP guy at RT66 races this week-end and he said go with stainless steel??? anybody heard of that for exhaust ???

I just went through the same deal and was told to stay away from stainless steel on the exhaust because the heat cycles will break the bolts.