I recently picked a 1964 3.5 hp McCulloch made Wizard from my grandpa. MLM 6904B. Flywheel will not spin, took lower unit off. Gears are rusted but do not look too bad, they turn and whatnot. This leads me to believe the piston is seized? Still working at tearing it down with my spare time.
Stuck motors can be stuck pistons, stuck bearings, stuck gear case and
can range from easy thru impossible. Every stuck motor is different. It is
best to have a parts motor to source replacements. If you are lucky between
the two you will have enough to make one that runs and looks good without
Proceed with care, take notes and pictures as you delve into problem. Treat it
as an exercise in patience between you and motor...first to lose temper