To offer a little food for thought on the original topic, here's a
picture of the rotor from the motor which I'm proposing to use as an idler:

http://www.mythic-beasts.com/~cdt22/lse_rotor.jpg

I dismantled the motor to give it a good clean, repaint the rusty bits
and check the bearings. That's a 10" ratchet in the picture and the
rotor weighs 30 lbs, so it's pretty sizeable. Gunner and Jim may well be
right when they suggest that the rotor itself will be plenty adequate as
a flywheel.

By the way, the motor is rated at 2.5 hp at 940 rpm.

Best wishes,

Chris