Steve wrote:
I have a 1983 Allis Chalmers 914H tractor that has been a trooper for
years. When mowing deep grass when the outside temp is hot the enging
makes a rapping noise and suddenly binds.

Make sure the cooling fins aren't blocked (maybe with grass?), the timing is
correct and the mixture is not too lean. These are among the things which
can cause overheating.