Did you have any residual voltage? If there's no voltage at the armature terminal there won't be anything to kick off the field current when it's grounded. Try checking from F to A with an ohmmeter with the wires disconnected- - - - -you should get a reading somewhere in the 5-10 ohm range. Also, try polarizing again, this time without letting the pulley spin. Apply battery voltage to the armature terminal for a second or so. You'll get a pretty good flash, but that won't hurt anything for a short time.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!