XR600 stuck in gear

[pismorat]

I'm looking at putting my '95 XR600 engine that's bored out to a 642 with a Hotcam in an old 350X frame. I've started some of the conversion work to the frame, but the issue I'm having with the motor is it was stuck in 2nd gear. The shifter would just spring back and forth. I pulled it all the way down and cannot find a thing wrong. The gearshift spindle seems to be in working order and shifts fine now when I do a dry run on the bench. I'm nervous to put it back together without changing anything cause it'll most likely happen again. The 600 was a runner and this problem happened on its last ride. Any ideas?

[El Camexican]

I'm not a Honda guy, but most bike/trike manual transmissions work the same way in that there is a shift mechanism which rotates a shift drum and then utilizes a number of springs to return and hold everything back and into place. The shift drum, which has a groves cut in it, moves shift forks back and forth on polished shafts which are held in place between your cases, The forks are what move the gears of your transmission back and forth on their respective shafts. The gears on these shafts engage with dogs, or oval shaped extrusions that match up to slightly larger shaped cutouts inside other gears.

When a transmission will not go to the next gear, or is not staying in gear it is almost always because the fork shafts are bent and not allowing the gear dogs to properly engage in the receptive slot, or the dogs and slots are worn to the point that under load they cannot stay together (this is where undercutting a transmission is needed).
Because your transmission wouldn’t come out of second gear it is unknown if your shift drum did not properly return to its next position, or if you have a badly damaged shift fork, or any other problem. Almost any transmission will shift on a bench, but unless you have a lot of experience with them you won’t be able to tell if there is something wrong by just “feeling” the dry run shifts. Once you load powerinto a transmission is when the problems jump out.

The bottom line here is that you should take it apart and measure and inspect everything as there is a VERY good chance that you will have this problem again soon after you start riding. Transmission problems tend to get worse very quickly and a something as simple as a bent fork shaft and turn into a set of gears after just a few botched shifts.
You may also want to search transmission problems for this particular bike elsewhere as the problems others have had may point you towards the cause of your problem, but you should still inspect everything while you have it apart.