Hi Gary.. Looks like you have a problem, hope you didn't pay too much for this load of trouble. '53 model year should be a bike with a Plunger Frame.
The gearbox is a simple design but prone to gear selection problems due to wear on the camplate and the rocking arm that moves it. Even using gaskets that are two thick alters the geometry of the selector mechanism. One possible cause is that the box has not been assembled in neutral. This ensures camplate and selector claw at least start in the right place. The pedal should be recessed into the outer cover. On later swing arm gearboxes the pedal shaft sticks out proud of the front face.
The plunger gearbox has a splined shaft carrying the pedal on the outside. Inside a forged member operates two opposed pedal return springs in the outer cover and a ball ended rocking claw on the inner cover. This claw engages with matching lugs on the camplate. The later swing arm gearbox is broadly similar, but the camplate and matching selector mechanism are completely different. Swing Arm camplate has toothed engagement with the rocking quadrant, the other end of which engages with a spring loaded claw on the pedal shaft.
The camplate position for gear selection controlled by a plunger in a cylindrical housing that sticks down under the box. The plunger pressure on the camplate is adjustable by releasing the locknut, and screwing the housing until it is at its basic setting with just a couple of threads showing. Take it off and check the spring loaded plunger is free and undamaged. You may be able to identify the neutral notch in the camplate...its the smallest one, so see of the gears will select with the plunger removed. The plunger aids camplate rotation, so you may have to help it with a bit of a push.
If you have to dig deeper, look for worn,damaged parts and incorrect assembly. The forged member on the splined pedal selector shaft is secured with a bolt and tab washer. This is often loose on the splines, so a source of lost movement.
The good news is that the box can be stripped down to its bare bones while still in the frame. If the box needs changing, on plunger frames its an engine out job.
Hope this helps, head over to the intro section tell us a bit more of how misfortune came your way.
Swarfy.
