Screw-hex 3/​​8-16 X 710-0520

Remove battery, seat and deck to expose drive pulley tensioner assembly
Release tensioner spring from right side of box frame.
Unbolt Flange nut on the bottom of the tensioner pulley to remove the pulley.
Insert new pulley with the long side of the center collar facing down and the short v-belt in the pulley grooves of all three pulley assemblies.
Insert screw downward through tensioner pulley and mounting bracket. Secure with flange nut.
Re-attach tensioner spring from tensioner bracket to right box frame.
Replace deck, seat and battery

Please note, this was just the beginning of my journey. All because the lawn mowers variable drive slipped so badly it would not move sometimes.

After replacing the above-described tensioner I discovered I still had problems and that the belts were bad. I ended up going back and replacing them. This improved but did not completely correct the problem and I then I discovered the variable drive pulley assembly was also bad.

So a word of advice. If you get into this variable drive you may want to do the whole thing. Tensioner, variable drive pulley, the bearings for the variable drive pulley and the belts. By the time any one of these items goes bad there is a very good chance that they are all worn out. You will likely save yourself the trouble of repeatedly tearing it apart if you do the whole thing.