Can my cracked block be repaired?
My 1949 Lincoln Cosmopolitan was overheating, and I thought it was a head gasket, so I took off the head on the passenger side and discovered that it has a cracked block. It is cracked from one of the stud holes to the back cylinder, but it is not very deep down the cylinder wall. These engines are few and far between, but friends have told me that repairing the block is out of the question. I hope they are wrong. What is your advice?
It is technically possible to make such a repair, but most old engine builders would not recommend it in your situation. Cast iron engine blocks can be welded, but they must be heated slowly to cherry red, then welded and then cooled slowly over a period of days. This takes skill and experience that is hard to find these days.
Also, where the block is welded together in the cylinder bore it will be harder than the surrounding metal. You can install a sleeve which would involve boring out the old cylinder to accommodate it, but then you are stuck with the fact that the sleeve is likely to expand and contract at a different rate than the block, and will be installed with a pressure fit in the first place, so you will likely have leaks again.
There are other techniques, such as spray welding and even brazing that have been tried, and my understanding is that they may work—for a while. However, most machine shops will tell you that the repair is likely going to be temporary. I have even heard of people repairing cracks with JB weld, but especially in your particular situation I don’t imagine such a repair would hold up for more than a matter of minutes.
If the crack were into an intake valve seat, a repair is certainly doable, but such a repair would not likely be satisfactory if the crack were in an exhaust valve seat. And yes, you could put in an insert valve seat, but that will likely be a temporary repair too, due to uneven expansion from heating and cooling.
Cracks can also be pinned, and that is a situation where holes are drilled all along the crack and threaded pins are installed. After that, the pins are undercut, a locking strip is installed and the block is peened over it. This sort of repair is best done by a pro, but there are kits for sale that will allow you to do the job yourself.
However, in the case you stated, it may not be possible. Nevertheless, if you want to learn more about the procedures involved call: