Discussion Forum - Northstar Chevelle Club

IF... and thats a big IF... there's enough "meat" in either the stud or the "lug/boss/base" (where the stud grows out of) you may be able to carefully drill it, and then using a blind hole tap cut some threads in it.
You'd only need 3 or 4 complete threads for something like a 10-32, or maybe a 1/4-28. Then make a stud from a machine screw (cut the head off) and either lock-tite or JB it into the threaded hole. Use a nut & small fender washer to mount that location.

Then to get really tricky about it, just hot-glue one of the stamped tin nuts OVER the machine nut to make it look factory.

I've done a few repairs to castings like these... a few tips:

Decide on the size of replacement stud you're going to use/make. In this job I'd probably go with 1/4-28. (fine thread, 1/4").
- consult a "drill and tapping" guide, and use the proper size bit for the threads of the replacement stud! You've only got ONE shot at this!
- purchase the proper size bit, and **important** what's called a "bottoming tap" of the correct size.

You probably won't have enough depth of hole to even get a standard tap to start - the point will bottom out before it even cuts one thread... but with this soft material, a bottoming tap should get started pretty easily.
(A bottoming tap has very little - if any - taper at the point. They're nearly flat across. They are designed to run into an already established hole, and cut threads all the way to the bottom of the hole. They "finish" what a standard tapered point tap cannot access.)

If you can't find a bottoming tap, you can "make" one with some careful grinding. Chuck the standard tap in a drill motor, and while spinning it at high speed, take the point of the tap nearly off on a fine-grit grinding wheel.


- protect the piece, and clamp it securely to your workbench. Have wood or cardboard under the new stud locations. Try and get your working location as level/flat as possible
- use a coarse mill file, or a die-grinder/dremel with a carbide bit to just barely level off the stud stubs **USE EYE PROTECTION**
- using a center punch, make a light divot in the exact center (as possible) of the old stud location.
- mark the bit with a flag of electrical tape for your maximum depth. Don't forget about the point on the drillbit!... or use a clamp-on depth stop.
- drill the hole to the proper depth.
- blow out the chips, and fill the hole with thread cutting oil, or a light 3in1 type machine oil.

Now the fun part. Getting a bottoming tap to "start" isn't easy. Getting one to "start" squarely is harder.
- With gentle pressure and a clockwise twist put the tap to the hole. Try and get 1/2 to 3/4's of a turn cut.
- twist 1/4 turn anti-clockwise to break the "chip" you've created.
- continue cutting clockwise and chip breaking until you feel the resistance of the bottom of the hole, or the crud/chips in the bottom.
- remove the tap, and blow out the hole.
- run the tap back in and clean up the threads.

Luckily, this type of pot metal casting cuts threads easily.

- blow out the chips & oil, and clean the hole thoroughly with carb spray or brake clean.
- make your new stud from a bolt or machine screw
- install your new stud with some lock-tite or JB-weld
- step back and admire your workmanship!

Dave Seitz wrote:

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Degrease the part and make sure the holes are clean a drop of Locktite blue can act as a lube for the stud. They do make a stud to do what you need but it is not available everywhere. What John said about the drill size for your tap will be aprx. 75% of hole diameter, so a 1/4-28 will be in the ,201-.211 range depending on thread needed.

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Thanks Dave.  Would the stud be available only to collision shops or something like that?