Need advise on stuck nuts...(exhaust)

In the process of replacing the pipe between the manifold and cat on my '92 Volvo.

So of course, I need to take the pipe off the manifold, and the nuts are on studs into the manifold.

So I need to "do this right" the first time...if I snap a stud, it's off to the garage with the car since changing the manifold / replacing a snapped stud is beyond my shade tree capability and/or "convience" (I'm not laying on my back on my gravel driveway with little clearance to do it!!!!)

Been hitting it with PB blaster. I'll be buying the metric impact sockets & extension (hopefully the used tool place in Worcester will have them before I go to Sears!) so I can attack it with my impact wrench.

But before I put the impact wrench to it, I want to heat the nuts first to minimize the risk of breaking a stud.

Is this something I really should rent a oxy-acetylene setup to heat up...or would a simpler torch like a MAPP be sufficient? I have a simple Bernzomatic propane torch now, but I'm a bit lery it has enough gusto.

Nuts are about 5/8" (used by english ones just to get a feel for the size to make sure I buy the right metric ones...figure I'll get a 16mm plus a 15 and 17 just to make sure I have the right one!

Anyway, I'd prefer to be safe then sorry...but I'm really tempted the MAPP would be simpler for me to handle than an Acetylene one (I have a *little* experience with Acetylene...but not much!)

Thanks for any advice...and I have a few days :) Using the truck for now, parts aren't in till tomorrow, and the used tool place isn't open to Wednesday afternoon so I have some time to plan!

I will assume this is a 240 series, otherwise most of my comments do not apply.

The size of the hex should be 15mm, the thread size is 10x1.5mm just in case you will need it. You are correct you will not be able to get a nut splitter in this area, it will also be very difficult to chisel or cut (Dremel tool, etc) off the nuts without damaging the studs. The nuts are special and have a locking flange that will bite into the flange on the head pipe. If they need replacment get new ones from the dealer. Standard nuts have a habbit of loosening over time and you will be replacing the gasket again.

I have done a number of these and have managed to do almost all using a 1/2" impact wrench. Make sure you get the socket firmly seated on the rear nut, this one can be difficult to reach with just a straight extension. Hit the studs with a wire brush to get off the scale, then use PB and let sit for a while. As long as you can get a good bite on the nuts, you should be able to get them loose. The studs are pretty tough and rarely twist off.

Good luck...

Or is it they're more forgiving of any damage to the studs (even after running the die over them).

Car has 132,000 miles...knock on wood I won't have to do this job another time :) A friend of mine bought it for his college-aged niece who went, "Yeeeewwww...a Volvo?" and turned it down...so it sat in his yard for 7 months. Previous owners only put 3,000/year on it for the last several (lived & worked in the same city). I'm putting 100 miles each workday on it so the exhaust should be much happier now :)

Sure is nice having two vehicles finally -- using my pickup while the Volvo is up on blocks waiting for me to finish the job!

One of your biggest enemies is the paint, dirt, and corrosion that's on the exposed portion of those studs. A "rethreading die" of the appropriate size, which you can get from just about any auto supply store, used to clean those exposed threads will make a world of difference.

But even a rethreading die won't clean out all the crud that's right at the juncture of the stud and outer flat of the nut. A stainless "toothbrush" type wire brush (or the itty-bitty wire wheel on a Dremel) will get most of that.

Then, while you've got the wire brush out, clean out the area where the nut meets the washer and the washer rests on the exhaust pipe retaining ring.

Once that's done, fire up the engine and go have a cup of coffee.

When you finish the coffee, shut off the engine and soak the washers, nuts, and exposed portions of the studs with PBlaster. Wait five minutes, and spray them again. A few gentle taps on the ends of the studs would be a good idea; you don't want to hit them hard enough to break anything or deform the studs . . . just tap, tap, tap. Another five minutes of waiting and another soaking with PBlaster and you put your tools away and allow the engine to cool.

Come wrench time, use whatever socket or box-end wrench fits the nuts the most snugly. Don't worry about "metric or Imperial??"; just use what fits best. (Arithmetic says that 5/8 inch is 0.0049 inch smaller than 16 millimeter, but with manufacturing allowances and tolerances it's possible for a 16 millimeter wrench opening to be smaller than a 5/8 inch wrench opening.)

Six-point wrench openings are preferred if nut-to-wrench fits are equal, but I'd rather use a tight 12-point than a sloppy 6-point.

A few gentle hammer-taps may allow a socket that's just a skosh too small to fit by hand to seat on the nut.

Spray more PBlaster.

Be sure that the wrench is FULLY seated on the nut, NOT half-way engaged or angled.

Use gentle force on the wrench to "wiggle" the nut tight-then-loose, tight-then-loose, tight-then-loose for a few moments before concentrating on the loose. It's ok if the fastener moans and groans a little, but loud squeaking is a request for more oil.

If the stud wants to unscrew from the manifold instead of the nut unscrewing from the stud . . . let it. A new stud is easy to install.

Then, for your new installation, use brass (even better, if you can find them, bronze) nuts and a high-temperature anti-seize compound.

John

Carol

I might however be able to get up in there with a flexible shaft Dremel tool...

Keep the ideas coming!

Dug