Helping a mate build his race engine and there's a buggered thread on the water pump in the aluminium block. Someone's had a thrash at it in the past with a drill and tap so there's not enough material left for a helicoil. We decided to make a stud by cutting the head off a bolt and bonding that into the hole with JB Weld. After 24 hours I tried putting a bit of torque onto the nut that fits the stud and it just pulled out. The JB Weld had set to about the consistency of plastic but nothing like rock hard or enough to hold the stud in. BTW I've ground undercuts in the hole so any filler that sets hard can't pull out.
So maybe the JB Weld was a bit old, my mate had had it sitting around for ages with a bit left in the tubes and perhaps it's gone off. What's the best stuff for a rock hard bond that might hold a stud in well enough to let us put a nut on and torque it up?