My 1982 F250 351w needs a new Y-pipe for the exhaust system. The nuts near the flange next to the manifold are very badly rusted (almost don't even look like nuts). I was wondering what is the best way to proceed. I do have a torch setup, but if I burn them off, how would they be replaced? Do the nuts attach to studs and if so how bad are the studs to remove?

Any help greatly appreciated.

 

Find the best fit using a true hex socket, not a 12-point. It may be metric that fits best. And then try to take it off 'cause many times they come of fairly easily. If not, heat the nut with the torch and try again, maybe hitting the break-over with a hammer to break it loose. If not, cool the hot nut with penetrating oil. Reheat/cool with oil/etc and it should break the rust bond.

 

As Gary says, heated (red) then quenched completely cold again, followed with a shot of WD40, they will almost fall off.

Getting to a red heat, & holding that for a few seconds, breaks the rust down into a powder.
But the cooling right down is equally important.......if the parts are still hot the threads will bind & tear themselves up.

 

I know I've looked at these things several times and thought to myself..."these are never gonna come off"...but like Gary said...they are usually not too bad.

Get a good hit it with some penetrating fluid, like PB Blaster, a few times (maybe start a day or so ahead of time to let it soak in) and get a good grip on it with a 6 point socket and I'll bet they come off easier then they look like they will. They should not be on there with a lot of torque.

Don't force it though...if they dont seem like they want to break free, hit it with some more Blaster and try again later. Or try the heating and cooling. But if you break/twist it off, to answer your last question, no easy way to replace them....that's how I ended up with headers on my truck.

 

I have had the worst case happen several times, so if you prepare yourself for it, maybe it won't be so bad when it happens. When they twist off for me, I just take the complete manifold off, put it in a vise, center punch the broken stud, and take a small drill bit and carefully try to drill in the center. Then keep working up till you get the correct size hole to tap the threads. Sometimes you are working with a blind hole(dead end in the bottom) and sometimes the hole goes all the way through, which gives you different options sometimes for dealing with it.

 

Which, of course, is yet another adventure in trying not to twist those manifold bolts off . Twisted the head off 3 of those little guys on my last job...which was much better then them snapping off at the head. At least when you twist the head off, you can still get the manifold off, and then deal with the stud left there.

 

Thanks for all the input. I guess I'll try heat followed by some PB blaster. The manifold bolts look as bad as the Y-pipe nuts... I just hope it doesn't come to removing the manifold.

Thanks again.

 

Rememeber what Gary stated...it is common for corrosion to actually reduce the size of the nut, due to material loss. If it's a 1/2" nut, you might be able to get a 14mm (I think) socket to fit bettter.

 

1/2" - 13mm....
9/16" - 14mm....

Vise grips - any....

I have had to use all the above methods at one time or another. Best results have been a hotwrench and PB blaster soak.

When I had to take off the manifolds for the same y-pipe changeout, I had two manifold to head bolts break off on the drivers side. Luckily both had some of the bolt still sticking out of the head. Heated them with the torch red hot, cooled with PB blaster twice, then grabbed them with vice grips and they came out. One of the manifold to y-pipe studs broke off flush with the manifold and had to drill and retap.

On edit: Heating the bolt/nut red hot and cooling with oil actually hardens the bolt/nut making them stronger. The carbon from the oil is "absorbed" into the bolt/nut increasing hardness. When you see parts that are heat-treated, thats how it is basically done. Heating to red hot and cooling with water tends to make the metal softer as some carbon from the metal is lost as it is heated.

 

Not exactly...what you are describing is called quench hardening. The quenching agent can be either water or oil, or other materials, or a combination. The rapid cooling, or quenching, caused a change in grain structure (from a common grain structure to a more precise structure such as martinsetic type). The quenching does increase the hardness but by chainging the grain structure only...not the chemical properties of the metal itself. It also can cause the metal to become very brittle and therefore most metals that are quench hardened are then tempered to increase strength. The quenching medium (water or oil) actually changes the quench rate, or rate at which the grain stucture changes. Water is faster than oil.

To harden do to the addition of carbon, is called carborization hardening...or commonly called carborized. This is a process in which the metal is brough to a specific temperature and a high carbon content material is introduced (usually charcoal or carbon boxite) and the metal is then soaked and the cool down is then controlled to maintain a specific grain stucture. In carborization, the hardened material is only a specific depth of the material, usually only a few mils deep. This is also called case hardening as it forms a "case" on the metal. This is usuallly only done on large components where you want the core of the component to remain softer or stronger and able to take more torque while the surface is harder to resist wear.

You can also introduce carbon to harden material during the alloying process, then the component has a more homogenious hardness to it.

So when you heat a bolt to red hot and then quench it with oil..you are indeed hardening it due to quench hardening...but without a further tempering process, it becomes brittle.

 

Thanks for the specifics, I knew there was more to it. I am not a metallurgist.

 

you were right on it....I would call it a strike

 

More like a foul ball in my book.

 

Way to go, Kev! Now that you say it I do remember all that stuff from my Mech of Materials class - back in '67. But, I always had trouble remembering which was which - martensite and austenite.

 

Oh yes, it's not all right there at the top of my head, I have to refer back to some old material myself!!