do I have a mac 5 motor?

[ted johnson]

In those days, Mac rings had chrome faces, and with stock factory clearances, needed a slow speed, oil-rich breakin for at least an hour. We were used to the thick, iron rings on Mac 5's and 10's, as well as the cross-scavenged engines. Take 'em out of the box, mount 'em, run 'em slow for ten minutes and have at it. What usually happened with the chrome thin rings, is that they had a bit of a rounded face to the chrome surface, and thus had a line contact with the cylinder wall until they seated. With the line contact, the heat wasn't well transferred to the iron liner, and the piston got hot enough to melt a small area which got dragged down over the rings. This pinned the rings, ruined the piston and cost a few hours and a few more dollars to fix. The cylinders always cleaned up fine with a light hone. The honing increased the skirt clearance as well as deglazing the bore. An hour with a new piston and ring set and you were ready to go. I must say that Pop built a pin pusher, and he and I got real good at replacing the bad pistons! When the all steel rings appeared, the issues went away.
P.S. You gotta remember, we were all direct drive, so when an engine stuck, the rear wheels slid for a LOOOONG ways! When the engine cooled, it'd turn with no compression. Ted