Cyril,

The plot thickens...Cooling fins assume that there is some air blowing past them. If you are running with a flywheel without anything to stir the air, there is no way the cooling fins will be effective. Racing cars use heat sink heads successfully because they are moving.

My guess is that had you been using an iron/steel diesel instead of an ABC conversion, you would have burned up your engine by now because of thermal runaway. Aren't the other guys having problems?

You might consider setting it up with a prop, as suggested, then run it in your tractor by starting, making the pull, then shutting down before it can overheat (if that's possible).

Good luck in any case.

George