John Deere lawntractor will not crank

[ATHiker]

I have a John Deere lawn tractor which will not crank over.
Details
 It was working fine and after shutting it off to empty crass, it would no longer crank over

Checked so far
 Jumped the solenoid just sparked
 Replaced the battery
 Took the hood off, and watched as the Starter motor engages but will not turn the crank
 Pulled the sparkplugs to remove compression and found I cannot turn over the engine by hand

Any thoughts?

 

[Rivets]

Sounds like a tight engine, but let's do a couple of checks. I assume you checked the oil level. Is it overfilled caused by a bad seat on the carb allowing the gas to enter the crankcase? Is the PTO off? Have you checked under the unit to see if the belt has jumped and wedged tight? Let's not assume the worsted until we check the simple things