Low air flow is a common cause of blower motor failure. Having talked
to many motor manufacturers at seminars, all state heat is the primary
cause of failure. With 240 volt system, I assume you have a heat pump.

What is making your motor run hot? If the motor does not have enough
air flow to cool it, it will overheat. Primary reasons of low air flow
are restrictive air filter (1" pleated or 1" washable electrostatic),
dirty air filter, undersized air filter, undersized duct system,
registers closed off in rooms you are not using, replacing system with
larger system without increasing (replacing) duct system, undersized
indoor unit, reusing indoor unit when replacing outdoor unit.

When you replaced the system, did they do a manual J load calculation,
or did they use the dreaded 500 sq ft. to the ton rule? Did they
measure the air flow from the system with an instrument more accurate
than the hand (handometer)? Did they replace the indoor unit? Did
they install a new air filter system (They can be restrictive, beware)
Did they install new ornamental grilles, especially wood ones (They can
be restrictive, beware). Did they put in a bigger system for any
reason?

Answers to these questions can help with diagnosis.

One other thing, did anyone measure the amps on the new motor(s) when
they were replaced to see if they were using more power than they were
rated for?

Stretch