Another engine.... 20hp kohler magnum. Starter was turning painfully slow all of a sudden. So pulled starter. Bendix had permanently engaged the flywheel. (The solenoid isn't part of the starter, ala Ford) Replaced with new starter. Now, the starter won't engage the flywheel, but is turning freely. Solenoid problem or starter (FWIW, all new starters have the Bendix down against the body and not up at the flywheel)
Grinds. just spins, or nothing but a click? Is the battery good? Bendix drive starters won't always engage with a low battery, since that initial kick of it coming on is what drives the gear into mesh. I know on Briggs stuff there's one starter and a handful of different pinion gears that have to be matched to the engine/flywheel.
Peeled the teeth off the ring gear? Drive gear on new starter is smaller diameter? Nose of starter doesn't go in as far? Lever from solenoid to drive is broken or out of place?
Turn the engine by hand about a quarter turn then see if the starter engages.
This starter mounts on the side. The Bendix is supposed to go up to the flywheel. It isn't. It's spinning freely. The battery can spin the cub motor fine so should be fine for this one. Starter appears to spin quickly. Just not sending the Bendix up. Again, the solenoid is not attached, ala Ford.
Can you run the gear up and down the helix by hand? Should move easy. The only other thing I can think of is you somehow got a starter that is spinning backwards, try bench testing it, gear should snap up when it spins up.