The design of the combustion chambers of the stovebolt engines makes them suceptible to getting hairline cracks, especially if one runs a little low on coolant and overheats. Cracks allow combustion gases to get into the cooling system, resulting in more overheating which leads to more cracks, so it's a vicious cycle. Most of the cracks are repairable, but it's an expensive process that requires specialized welding and/or machining facilities. Cylinder head repair is beyond the capabilities of all but the most dedicated hobbyists because of the cost of setting up the procedures, and there's a fair amount of skill necessary if welding is the repair method of choice. Cast iron isn't the most welding-friendly material in the world! 50 years ago, a cracked head would get scrapped and another head would be acquired from a salvage yard for a few bucks, but those days are long past. As the engines get older, replacement supplies are drying up.
Jerry
