Originally Posted by aspeed

Brass expands faster than aluminum, and it gets looser as it heats up as in an ABC. That is the great part of the ABC. A few lean runs on a steel set can ruin them. An ABC has a better chance of recovery. AAC is ok too. better for pit stop restarts, but does not have the effect of saving a motor like ABC. A chromed steel liner is a good thing too, after it has worn out. It seems to hold the heat from a lean run better than a regular steel set. Lean runs are bad news though all around. Having flown a lot of control line, a lean run in steel P/C has ruined a few motors on me. Lots of castor is ok, but I normally use it after it is worn out, just to make the motor useable. The old steel ones, I normally liked to lap out for a nice fit so they would not seize up, and they would break in easier. Of course I flew speed, and friction was the major reason for a loose fit. In some cases castor was forced on us in the FAI speed event. It was ok but needed to be devarnished quite often. TDs are bad for that too. That was a cause of overheating too. This being a Fox thread, I would have to say that could be the cause of it overheating when hot, but having said that, Fox users seem to swear that the Foxes need the varnish. I will stay out of that one.