Small Engines (Lawn Mowers, etc.): Won;t crank, mtd lawn tractor, starter solenoid

Question
Hello, and thank you for your time!  I have a 7 year old 20 hp MTD lawn tractor that won't turn over. I either get no activity at all, or a clicking sound from the starter solenoid under the seat. Tested the battery, it's fine. Checked the brake and seat safety switches, they both have continuity. Ground is good. Turn on the ignition switch and I get my 12 vdc to the solenoid. I detached the solenoid and hooked her up to an external 12vdc/27amp power supply I have, and she clicks and provides continuity throught the hot posts, but I don't get the constant clicking that I get when I try and start the mower. I have cleaned all the contacts I can find...and just feel stuck.  Any suggestions are most appreciated. Thanks again.

Answer
With the spark plugs removed, can you turn/crank the engine by hand?

With the spark plugs removed, will the starter turn/crank the engine?
Did you check the starter pinion gear?  I have seen some of these stick and bind the flyweel.
Let me know.
Eric