Hi, In trying to install booster plate on 71 350 engine 2 of the bolt heads (the ones in holes that go right through the timing cover/water pump housing) have snapped as threads are seized in the cover. If I were to drill out and re-tap the holes what size thread will I need? Thanks.
I would not drill them out if part of the bolt shank is still there. Lots of penetrating oil, and maybe some heat. Grab what's left with a pair of vice grips and gently try to remove them.
Thanks. I tried penetrating oil for a few days and vice grips but I'll persevere and use heat as well.
A common trick is also to weld nuts onto a stripped bolt, but that might be bit dangerous when you have aluminium so close. Should you have to drill those threads should be 1/4" UNC.
So as an update I got 1 bolt out with heat and vice grips. I then invested in a cheap mig welder off Facebook marketplace and cut out a protective plate the size of the oil pump cover from a thin sheet of steel to cover the housing. (With hole drilled to go over the remaining snapped bolt). I then welded a nut to the bolt which snapped off on first attempt and on the second attempt it worked! So rewarding!
