This repair uses a screw sized 10-24 x 1/2" long round head.
Broken screws in the radiator bolster are a very common find and need to be repaired in order to mount the dog legs securely. Replacing them is not overly difficult but does require a little aptitude, time and patience. When all else has failed and you have to get the drill out, this is how I make the repair.
DO NOT drill any deeper into the bolster than necessary or you may penetrate the "wet" side and have water in your lap. Remember the new screws are only 1/2" long. Usually you can feel when you have drilled deep enough as you can feel the void when the bit exits the end of the original screw. But remember the new screws are only 1/2" long.
- Start by using a hammer and pointed punch to dimple the center of the screw and give a drill bit a good starting point.
- Begin with a very small drill bit maybe 3/32" or even up to an 1/8" inch if it is good and sharp. I use left handed drill bits for this job. Sometimes the left handed bit will back the screw out and all is well. If it does not back out on its own, step up the hole sizes until you reach 9/64". That is the largest drill bit I use for a 10-24 screw size.
- Once the hole is drilled to 9/64" its time to rethread. Using a 10-24 tap you begin to thread it into the hole being careful to have good alignment with the new hole to avoid binding or jamming of the tap. Slowly, turn the tap clockwise a bit and back up a bit to clear the shavings. The tap should feel resistance while cutting but not enough to feel like it may be in a bind. Do this until you have threaded enough to for the 1/2" screw to seat fully. If using a pointed tap you will need to go deeper than the 1/2" depending on the tap design you are using.
- Once it is rethreaded, clean out the hole with a low pressure compressed air (or vacuum) being careful not to get any metal shavings in your eyes.
- Fully thread in the new screw to verify it will seat properly. It is much easier to test the hole before the dogleg is installed. If it does you are finished and ready to install the dogleg.