Gear Shift Mechanism Problems

[Ovrman00]

I am not a real mechanic, but this is what has happened / is happening to my bike:

My 1966 CB77 (5500 miles) was having issues changing gears. Basically, when I shifted into 2nd, and sometimes even 3rd, my bike would shift into neutral on its own. I thought this was happening because of an issue with gears. I went to a mechanic so that he could check it out, but he didn't think it was a gear issue because the bike has so few many miles on it. While at his garage, on a test run, my bike locked up when I tried to move up into 2nd. The gears would change and the crank shaft would rotate, but the rear wheel would not rotate while in gear and the kickstart would not kick forward. Something felt locked. Thinking it was still a gear issue, we took the engine out and flipped it over. While in the process of taking off the Left Crankcase Cover and removing the Gear Shift Mechanism parts, my bike got fixed. We don't know what we did exactly, but after messing with the GSM everything on the engine was working as it should.

To make an already long story short...

We put the engine back on the bike and now it is having the same exact issue. I figure that if we messed with the Gear Shift Mechanism once and it seemed to fix the problem, but it happened again, than the Gear Shift Mechanism itself might be the problem.

Does anyone have any experience with the problems that might come about with a Gear Shift Mechanism and can you offer any suggestions? Thanks and sorry for the really long explanation.