I installed my racing beat downpipe / cat delete / presilencer friday night but I encountered a small problem along the way. When removing the 2 nuts that hold the exhaust manifold to the first pre-cat the one on the passenger side jammed part-way off and it demolished 5 or 6 full rows of threads, right where the nut needs to sit. Since it also removed all the threads on the nut itself I simply used that nut as a spacer and another nut from the factory exhaust on the end of the stud where there are still threads, but I was hoping to get under there and replace the stud so that I can have this all put together properly and I don't have to worry about this band-aid fix coming apart later.

I looked up the stud and it seems to be a special M12x1.25 threaded-on-both-ends stud, it doesn't look to be pressed in, but I am wondering what the best way to remove the existing stud is. When removing the nut I had to apply in excess of 150lb-ft to get it off the first time, and although I have a stud remover I think applying much more force than this is likely to simply snap the stud, at which point I will end up drilling and tapping which I don't really want to do (M12x1.25 taps are hard to find and are expensive).

Is the factory stud installed with some kind of thread sealant or loctite? Do I need to heat the stud with a propane torch before trying to remove it? Any tips would be appreciated

 

I would PB Blaster the dickens out of it and let it sit for a few days. You're probably going to have to heat it. I use an acetelyne torch.

 

Acetylene? Wouldn't that make the stud so hot it will just break/tear?
I'll start on the PB blaster tonight

 

No factory will put loctite on exhaust bolts.

Why? cuz they will eventually rust and stuck anyway, whats the point ?

if PB Blaster doesn't work (most likely won't,especially if its seized badly), then you need a torch, Heat the nut, use a water hose over the bolt, the heat/shrink effect will 90% of the time crack and loosen all the rust. repeat this couple of times, should be able to do it in about 1/2 hour. then just break it loose.

if you still can't get it off (round off threads and the nut just keeps spining/won't move), then your last resort is to grind it off with a cut-off wheel. this method always works but you gotta be careful.

 

The nut comes off no problem, and I have a stud remover which grips extremely well so I am not worried about being able to get a grip on the stud. My main worry is that the stud can't take the torque I will need to put on it and will snap off, then be nearly impossible to drill out and require an expensive tap to repair the hole.

I still need to order the replacement stud, but once it comes in I'll start PB blastering the stud daily (the rx-7 isn't my daily driver so it can just sit while I do this). Since the end of the stud I am talking about is secured to the exhaust manifold itself will the heat/cool trick work, or will the manifold simply absorb all of the heat I am trying to put into the stud before I can get a big temperature difference?

 

You willl thank yourself if you return that downpipe and buy the header. trying to screw around with hardware on 20+ year old exhaust especially those boat anchors they call an exhaust manifold is recipe for frustration and a lot of wasted time...

And start with the liquid wrench / PB blaster on a daily basis on the header studs on the motor till the header arrives.

I have a header that will bolt up with a stock cat location presilencer/racepipe for sale ...

 

Can't exactly return something I bought used, and I bought it mostly for the purpose of replacing the stock cats which had rusted through in several places and were falling off the car, so even if I could return it I'd be in a much worse situation

If the price is really good I'd consider changing the header for the HP gain, but goal #1 was to get this car safety inspected and out on the auto-x track to start having fun with it, and I couldn't do that with multiple exhaust leaks.

Right now it looks like I can fix this stud for ~$6 (maybe ~$15 if I have to buy new gaskets) if I can just get the thing out of there. It also doesn't leak right now, I am just looking to replace it for peace of mind.