Re: Water pump stud broke
They are screwed in. Usual problems with older engines and corrosion. You can drill it out, retap it and fix the problem. It takes time and concentration. Problem is the stud is a grade 5 which means it is relative tough steel, but not that tough. Slow running drill bit, lots of drill cutting fluid and lots of downward pressure....you want to have a shaving coming out continuously as the drill turns, not little chips, but shavings...that says you are making headway.....PB Blaster penetrating oil is not cutting oil, but if you have none it works great...can get at WW or auto parts store. Use a grinder to flatten the top of the stud before you start and then use a punch to ding the center. You want your drills to be as centered as you can get them.
Best course of action is to start with a small bit and go down about 1/2" in depth at least. If the drill quits bringing up steel shavings stop and move to a larger bit....aluminum is next and you don't want to drill too deep. Move up to a larger diameter and continue till you get about 80% of the diameter of the stud.
Then take an easy out and back it out. If you can't do that you can go ahead and drill out all the threads and into the alum with a larger diameter; still don't go deeper than necessary. Then, using a tap that you can buy at an auto parts store, using cutting oil, tap in an oversize thread and insert an oversize stud. Get the tap and see what the tap drill size is before you do your final drilling of the old screw. National Coarse threads are what's used in alum castings. Fine will strip out easier. Drill out the diameter of your water pump as necessary to accomodate the larger diameter bolt.
I'll do your homework for you:
If the existing stud is 1/4" diameter (0.250") it's thread will be 1/4-20 (20 is the threads per inch) for UNC threads. Moving up with the new tap would be the next commercial size which will be 5/16 and will be a 5/16 (.312") x 18 for UNC. The drill for that is the letter size "I" which is 0.272" in diameter. If you are lucky, you can get a kit with the correct tap drill and tap in one package.
Replacement with a stainless steel bolt would be best and adding a little anti seize wouldn't hurt. Permatex #2 would work and act as a thread lock, or a Locktite blue thread sealant. If you are in fresh water a galvanized steel, grade 5 (3 lines, 120 degrees apart on the top) would work with the anti-seize.
HTH,
Mark
