Tines not turning after replace worm gear in transmission

First, make sure the engine (really the clutch housing) is seated all the way down onto the transmission. It’s not very likely this is the problem, I’ve never seen these go loose (usually it’s an assembly problem), but it might be possible.

Another possibility us that the clutch is not working. If the tines stopped moving somewhat gradually, slowing even though the engine speed remained unchanged, it would be the clutch. If it was instantaneous — which you would have noticed if you were tilling — the woodruff key on the crankshaft has sheared.