Ok I see the problem, I need to make the sprocket side a bit bigger without messing up the shape of the key hole.

Also as luck would have it the leads on the larger motors are too short.. But the leads on the smaller motors ARE long enough. So, I bet if I just tap it with a soldering iron it will come off and I can switch them. The larger motors have what I think are little resistors that combine the +/- in series with the can itself. or maybe its some other way i'm pretty tired atm. they say 104, 10.4kohm? i'm studying this stuff for work/school so I only just know what I'm looking at but not much experience