Exhaust manifold to catalytic converter nuts and studs rust welded

[FireFox31]

Hello, does anyone have suggestions for removing the exhaust manifold to catalytic converter nuts and studs which are rust welded in place? I could cut off the exposed nut/stud in hopes of sliding the cat off the remaining stud. But I'd still have to unscrew the stud from the manifold which appears impossible. I might do better replacing the manifold but that's extreme.

Every job on rusty Geronimo involves this damage control thinking, committing to drastic measures which would leave me stranded if they fail. Here I am again. Thanks for your ideas.

[abscate]

Get that OXS out of the way, then Dremel off the nuts with a big slot, the bang with a chisel until the break

Those studs look horrible, but will likely be ok to re use, Volvo used really good steel on these

If slotting the nuts kisses the studs a bit, they will still work fine

Three cycles of hot / cool with propane, maybe 60 seconds per cycle first, of course

[dikidera]

It likely wont do much but still spray them with something like WD-40, let it soak for a while, then heat then try wrench, once they strip. Chisel it all the way.

[scot850]

I have a tool called a nut splitter which does the similar thing to the dremel. Having said that, in this case the dremel may be the best way to go as the nuts have no side profile for a nut splitter to catch on.

I wish you a load of good luck!

Neil.

[FireFox31]

Thanks scot850, I had no idea those existed. Looks like Kukko makes some great splitters, single and double edged. Single edge are also available from Gedore, Stahlwille, and Hazet at KC Tool. I ordered the Gedore 10 mm - 17 mm. Dealing with rusty parts is the biggest time sink during car repair for me. I'll buy any tools I can get to simplify this unnecessary step.

For now, I'll surgically Dremel these nuts off, hoping to free them from the studs. I have new studs and nuts, but I have to hope the studs unscrew from the manifold. Another tool I've wanted for years is a tap and die set so I can clean exposed bolt threads, clean bolt holes, repair holes after broken bolt extraction, etc. I especially need it for brake caliper fitting holes which tend to rust and clamp down on the fittings, preventing new fittings from threading in.

[scot850]

Best of luck!

Neil.

[FireFox31]

I separated the catalytic converter from the manifold by using a Sawzall to cut the studs at the base of each nut. The remaining nut fragments fell off leaving the clean cat flange mount points behind.

Does anyone have advice for removing heavily rusted studs the manifold? I have to get them out this weekend or I'm down a car.

I have a second manifold with stuck studs off the car to practice removing them. I had someone weld a nut to one and hit it with an impact, but the stud simply snapped. I'm going to try heat with the inductive heater but it's tough to wrap the magnetizing coil around the ear of the manifold which holds the stud. I may also try cutting off the small bit of stud out the back of the manifold to break that rust bond and remove those terrible threads. Lastly, I can try putting two nuts on the stud (barely fitting), turning the inner nut to loosen or the outer nut to tighten; anything to break the rust bond. Then I have to hope the threads in the manifold are still good.

How does an exhaust shop deal with studs this rusty? I need their trick. Thanks for your help.

[abscate]

Get the studs cherry red with oxy mapp a few times before you try twisting.

You can also drill them out with a sharp Co bit

[dikidera]

In addition when you have it all out and have a new gasket ready, try to use an abrasive brush or something which can smooth out and remove rust on the exhaust manifold flanges(both towards cat and head) so that a perfect seal is made with the gasket, otherwise you risk having an exhaust leak.

[FireFox31]

Thanks. After a few hours of practice, I was able to remove two studs from the spare manifold. Frequent applications of heat and oil were the solution. I used a Dremel to shave off the back of each bolt, breaking that rust bond and allowing oil to penetrate the clean cut. I used a blow torch to heat that cut back side of the manifold, expanding the threaded hole to further break the rust bond and allow oil in. I tried to unscrew them while the manifold was still hot, hoping it was expanded.

For one stud, I was able to use the two nut trick: Thread two nuts on to the stud, then unscrew the inner nut so it jams up against the outer nut and stops. Turning it further allows it to grab the stud and unscrew it from the manifold.

For another stud with bad threads, I had to use a #1 size bolt extractor hammered on to the stud, applied heat and careful, forceful turning. When the stud snapped (twice), I hammered the extractor on to the remaining stud and continued until the stud finally removed.

Hopefully the two nut trick will work on the studs on the manifold still up in the car. Their threads appear to be ok. I must first use a lot of heat and oil before potentially hurting those threads.

The real solution was, as abscate and scot850 mentioned, to save the studs by carefully removing the rusted nuts. Use a nut splitter, multitool for a flat cut parallel to the stud, or Dremel for a more awkward round cut on the nut. With the nuts removed, use an M8 x 1.5 die to clean up the stud threads. The threads are in decent condition under the nuts so could be reused.