Cummins uses a wet sleeve compared to Detroit's dry sleeve. The 72 was a pre FFC small cam engine. which means it did not have piston cooling. They were very prone to piston galling. That is when combustion temperatures got past the melting point of the piston and the piston actually sticks to the sleeve. The good news is that cummins parts are very cheap compared to Detroit and cylinder kits are sold individually..That is a cylinder, piston and rings. Whoever, the knocking you are hearing is probably a liner that is loose. When liners are installed, the liner protrusion at the top must be shimmed correctly and the counter bore must be correct which takes special tools, but it can usually be done with out pulling the engine. If you have never worked on a cummins, it is really not something you can do your self. Find an old mechanic who has experience with these old engines to help you. By 79 cummins had improved their engines greatly. They had FFC piston cooling, the big cam and improved turbos. And they were a lot easier to drive. Drivers had to constantly keep their eyes glued to the pyrometer to watch combustion temperatures to prevent this from happening. By the late 70's a pyrometer was no longer necessary and the engines had a much wider operating range. My first cummins was a 1964 model and I have used nothing but cummins and I have watched them evolve. You might want to replace the small cam with a big cam emgine. i am not sure what you mean by abusive use, but the old cummins could not stand abuse. I would be glad to discuss the matter over the phone with you to keep the posts from getting too long.
