Some months ago I spotted an interesting new product in an automotive supply. To protect the innocent (me), I shall call it freeze and free, although this is not its real name. What it is, is penetrating oil combined with a refrigerant. You spray it on the stud, or nut. The refrigerant evaporates and cools the stud or nut to -45 degrees. The part shrinks, and the oil is pulled in by capillary action. As I had no immediate need for it, and my garage is already too cluttered, I did not buy it, but did put it on my mental “must try” list.
As fate would have it, a few days ago, I twisted the 40 year old stud off a 40 year old iron exhaust manifold, leaving about an inch sticking out. Because of the close proximity of the starter and other stuff, using a torch was out of the question, so I purchased the freeze and free. I applied it a few times, following the instructions on the can. I expected the stud to frost over, like in the sci-fi movies, but it did not. I then applied what I thought was a reasonable torque, but the stud remained. Let’s face it, though, this was probably too severe a test for this product.
Reluctantly, I decided to remove the manifold from the car and finish the job on the bench. This required removing the clutch linkage, starter motor, chassis brace and other parts. I have learned through bitter experience that trying to save time by taking shortcuts such as not doing the disassembly actually requires an order of magnitude more time.
Heat is the normally accepted method of removing studs and nuts. Nuts especially. Heat nuts red hot, and you can easily remove them. In this case, I first tried brazing on a nut. The brazing did not hold. I then mig’ed on a nut. While it was hot, I held my breath, liberally sprayed the freeze and free on it, and ran away ( you never know what evil fumes are released when you heat refrigerants !!). This time, I applied maximum torque. Of course, the stud twisted off completely.
This left me with only one option – drill out the stud, and grind out to the thread roots. I’ve had to do this before. 20 or so years ago, I had to remove a dilivar stud from my 911SC engine case this way. I had gone the heat route on the stud, but it did not work. Somehow, applying lots of heat to an aluminum engine case with a torch requires guts, and perhaps I was not aggressive enough. My tool and die trained father made a drill jig for the 911 and I set to work. The dilivar material was tough. It required a carbide tipped drill, and lots of sharpening. I wondered at the time, if I had heat hardened the material with the torch! A diamond tipped dremel bit allowed me to finish the job. The whole thing took a few days.
Back to the exhaust manifold. I filed down the studs as close to the casting as possible. I center punched the studs. The stud was 3/8 inch, meaning the thread roots were 5/16. Using a 1/4 drill would give me a 32nd on each side, and I felt I could hand drill to that tolerance without damaging the threads of the casting. In most cases, studs do not screw down to the bottom of the hole, so there is normally a void under the stud. This should prevent you from drilling into the casting. The drill went through the mild steel studs like soft butter. I decide to use the diamond dremel bit, instead of going with a carbide burr. The reason is that the diamond burr takes off material slowly. Carbide will cut mild steel very quickly, and making a mess of it would have been likely. With the dremel, I ground out the stud until I could see the little lines of rust that were the casting thread crest. I did the stud that I had not cooled/heated first. After grinding, the stud thread helical unraveled easily from the casting. The other was not as easy. The thread helical was glued in place. I ended up have to re-thread. This had to done very carefully so as to follow the path of the existing thread identically. If I had not done this correctly, helicoil insert would have been the only remaining option.
The exhaust manifold is now back in the car. A very satisfying operation !!
pics to follow