Some water pump bolt holes go into the cooling system. It's customary to coat the bolt threads with gasket sealer to prevent them from leaking. If a bolt broke off inside the block, it is still going to seal that hole unless you drilled all the way through it. In that case, drill the entire bolt out, then tap it and install a Heli-Coil insert. Any auto parts store can sell you the kit with the correct size drill and tap for that bolt size, and they can show you how to use it. Every year when my students were putting together their first school-owned practice engines, they came in one day and found a bolt hole had "magically" gotten stripped out overnight. Hmm. Everyone had to install a Heli-Coil. They're easier to install into aluminum, but cast iron just takes a little longer to drill and tap.
Another approach is to weld a nut to the broken bolt. You'll need a wire feed welder and an acetylene torch. Propane torch won't work. The flame is too large and not hot enough. Grab a nut with a center hole slightly larger than the bolt diameter. Center the nut over the broken bolt. Use a small torch tip with a nice blue flame with a sharp point. The tip of the flame is the hottest part of the flame. Touch that tip to the center of the bolt to warm it up. The goal is to get the bolt red hot but it never will get that hot because the heat is being sucked away by the block. Nevertheless, heat the bolt for at least a couple of minutes. Stay away from the nut as much as possible. You want it to stay cool. If you're careful and quick, you can heat the bolt first, then set the nut in place with a pliers just when you're ready to weld. When the bolt is as hot as it's going to get, hand the torch off to a helper and immediately grab the welder. Feed the wire onto the end of the bolt and start to build it up. Stay away from the nut as long as possible. Don't stop welding because you don't want the bolt to have a chance to cool down. As the weld builds, it will fill the hole in the nut and eventually you will also be welding TO the nut. The nut will turn orange. That's ok, but stop welding before the sides of the nut start to melt. You need those sides to be in good shape so a socket will fit on the nut.
Welding works, not by "sticking" to the metal, but by melting the surfaces of the two pieces of metal with a filler metal in between. That's called "penetration". If you don't preheat the bolt, the heat from the welder will be sucked away before the metal of the bolt melts. You'll end up building up the weld until it melts to the nut but it won't have penetrated the bolt. That would be like putting glue on the piece of wood you're using to build a bird house, then assembling the pieces after the glue dries. The preheating gets the bolt up to its melting temperature sooner. It has to reach that temperature from welding before the weld builds up to the nut.
Once the nut is welded to the bolt, let it cool by itself for, ... Oh, ... About ten seconds, then dribble a little water on the nut. Don't pour so much that it floods the surrounding area. You want to shrink the bolt but leave the block hot. The shock from the water will help break the bond between the bolt and block. Use a six point socket, ratchet, and extension on the nut to turn the bolt out. If the weld didn't stick to the bolt and you twist the nut off, just grab another nut and try again. I've already had to resort to as many as six attempts before this worked. Sometimes this works better with two people, one to run the torch and one to be standing ready with the welder. Use a high setting on the welder to insure good penetration into the bolt before the weld builds up to the nut.
Sunday, March 18th, 2012 AT 5:28 PM