60" mower blade spins free

[MattEffinCameron]

Have a B2920 with a 60" mower deck, RCK60-29b or something like that

took the blades off to sharpen but when reinstalling one of them will spin freely by hand (while the other two are fixed) even when we have tightened down the nut on it all the way.

Any thoughts as to what might be the issue?

 

[85Hokie]

The cupped washers ........ they being used correctly?
Did the hub slide into the splines?

 

[GreensvilleJay]

gee 2 good, 1 bad...should be easy to see what's wrong.
Agree ,1st look at the Belleville washers, #140
or, hmm, is #150 splined into the shaft properly ?