if its an electric clutch the solonid that engages it may be bad, if its a manual engagment,the belt may be bad,or a spring has come off,
because it needs a 1600 vee dub engine in it to make it go faster to have lawn mower races
replace it
get a new one
You will have to put the rider on a ramp in order to get under it to replace the blades. For lack of a ramp, I leaned two 1 x 12 boards from the ground to the edge of my back porch and pushed the rider up so the front wheels would be on the porch. Had to lie down on the ground to do the work, but defintely worked ok. Regardless of which method you use, be sure and block the wheels for safety,
there is what they call a key that locks the wheel and axle together must had stuck on the old wheel
There could be many reasons why your Sears riding lawn mower won' shut off. The key could be jammed for example.
Try pulling out the spark plug and clearing the cylinder
your electric motor(I assume) probably wont have enough torque, That is on a Riding type mower, not a push mower, it might work on a push mower as long as its not self prepelled, because your motor probably still wont have enough torque!
not getting gas. clean\carb rebulid needed
check the front and back belt pulleys and if the elt is on the right side of the engager.
Perhaps it is the starter drive. That happened to my riding mower. Got the drive replaced, works fine.
Your flywheel key might be sheared