is the bearing on backwards???
what side is the snap ring grove in relation to the gear?
it should be on the outer most side away from both sets of gears on the counter shaft....right close to the bearing retainer c-clip.... if the bearing is on backwards, the counter gear will either...
1. be too wide to fit in the housing... or
2. the big set of teeth will hit the case before the snap ring grove is exposed rendering it inaccessable