One of my JTs has shifting issues where the trans simply doesn’t do what you want it to do. You can sometimes find a gear, and you can sometimes get it back into neutral but it is simply a mess. So I decided to split the cases to try and sort this out.

I have a spare JT engine with the top end froze up solid so I started by splitting that one open first since I have never done this before. Trans looked OK on that froze up engine. Then I split the cases on the engine that I am trying to fix. I think I have found the issue, but I would like to confirm it and also determine why it occurred, unless this simply happens from long term use. 

The link below shows some photos from both engines for comparison purposes. Hopefully the images come up in proper sequence to my descriptions below….

imgur.com/a/eI7Yhk2

The first image shows the shift drum circled in red.
The next image shows a stopper pin on the lower portion of the shift drum.
The next image shows how the stopper pin radially comes in contact with a boss on the side case.
The next image shows the boss with the shift drum removed.
The next image shows the stopper pin having rotated too far due to a damaged boss on the side case.
The last image shows the chewed up boss with the shift drum removed.

So would this damaged stopper boss cause my shifting issues?
Is this normal long term wear, or do I have other issues to sort out?
I see no other obvious issues with the trans parts.

Any help or advice would be greatly appreciated!

First, I've never worked on a JT1. : ) ...but since this is the internet...

I'm wondering if you have both axial and radial adjustment concerns.  I usually take the shifter arms in a drill and polish the contact points where it meets the case w/alum oxide red, then VERY fine emery cloth to a polish also.    

* Is it possible the shift drum is being "pulled/pushed" laterally by the alignment of the shifter arm? This ~may explain the movement further to the R side of the case and away from the stop.  Also, shifter arm maximum axial movement.  It may be able to move too far R/L. Shim necessary?

* Is the shifter adjustment correct and appear centered? Here is a video explain. Video of Shifter Arm Adjustment

UPDATE
I may have discovered the root cause of the damaged boss on the side case. I have a different shift drum on the one with the damaged boss. That particular shift drum is a hollow shaft and the stopper pin is press fit but it extends into the hollow shaft. That particular stopper pin has considerably less protrusion than the one on my spare engine. Like it only protrudes half as much.

The shift drum on my spare engine is a solid shaft with the stopper pin pressed into a blind hole so it can’t be forced any deeper and ensures that the pin keeps the proper amount of protrusion. The solid shaft also has an additional window machined into it and I assume that was to reduce the mass of changing it to a solid shaft. So maybe I just discovered the root cause being that the stopper pin had worked its way deeper into the drum and minimized the amount of extension thus allowing it to chew away at the boss and ultimately allowing it to rotate too far. I’m still interested in your thoughts/opinions.

imgur.com/a/WmzHsMe