Are the nuts holding on the blades reverse threaded?

Troy-Bilt Lawn Mower Blades Won't Engage - Model ...

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Most Frequent Causes for Lawn mower blades won't engage. See All Lawn Mower Parts for model 13AP60TP766. Cause 1 PTO Clutch. If the blades don't rotate the electric PTO clutch might not be engaging. ... Lawn mower wheels don't turn ...

Turn mower on it's side with the carb facing up (otherwise fuel will pour out of the carb) There should be one bolt holding the blade on, remove it and the blade will come off. Install new blade in reverse order. Use an impact wrench if you have one otherwise use something to keep the blade from rotating when removing the bolt with a wrench.

are your blades engaged when you try to do this??
if so it is a back up safety feature from factory,turn blades off and try?
Or put the ignition switch in the position that will keep the mower running when you go in reverse with the blades on or push a button on dash when you go in reverse,probably not on yours just some of the features on some models and just something to look for on yours

Sounds like either the switch for the blades is not shutting off the power to the electric clutch or the clutch itself is not disengaging. I would shut the mower off and unplug the wire to the electric clutch and then start the mower and make sure the blades do not turn you may have the belt for the blades on the wrong pulley and it might be causing the blades to turn. Hope this helps.

UN BOLT CENTER BOLT AND/OR ANY OTHER (SOMETIMES 2) BLADE HOLD ON BOLT. MAKE SURE NEW BLADE IS:
1. CORRECT FOR MACHINE
2. RIGHT SIZE
3. USE LOCTITE THREAD LOCK ON BLADE BOLT THREADS BEFORE REINSTALLING
4. TORQUE BLADE TO MANUFACTURE SPECS
5. GO CUT THE GRASS

Sounds like a bent shaft, or bent blade.
Also sounds like the part that holds the blade to the shaft is sheared, and allowing the motor to run faster than it would if it is turning the blade properly.
Hope this helped,
Please rate me

remove the front black plastic plate that is stamped self propelled and replace the wheel drive belt that attaches the engine pulley (above blade) to the transmission pulley (found under the cover). When you buy the belts, pick up two or three as I seem to go through a couple per season. Hopes this helps

Bet on it- you might try adding an additional nut of the right size/thread or several washers to utilize the remaining healthy threads.

Take the three screws out of the belt cover. One screw in behind each back wheel. The other is under the mower near the shaft to blade. Remove the tension spring off the transmission. Then remove blade and the cover comes off. You then can put the belt back on. Sounds like fun don't it!

is the drain plug on a troy bilt 6.5 hp ontop of the blade in the right hand cornor