Gearbox troubles? if yr bike is jumping out of gear, it just might not be the cruciform!! . but if you don’t fix it, the cruciform probably will die shortly. so here are some things to check.
1. take the sel. box cover off.
2. look at it. you’ll see a little ‘wheel,’ for want of a better term, with notches in it. you’ll also see a pawl (an arm with a roller on its end) that is sprung and held in place by a screw. keep looking at the pawl, right where it’s held by the screw.
3. turn the gearchange lever and watch the pawl. you want to see the pawl pivot only, not move in and out (relative to the engine case). this sort of slop means the cruciform may not wind up right in the center of the gear, and then jump out under load.
the good news is that a new pawl and the pin that holds it will cost you only $4!! and you don’t necessarily need to buy a new sel box! whooopee!
4. if that’s not it, take the sel box off. loosen the nuts on either side of the box, then get ready to catch the lock- and plain washers. maybe put a rag on the ground under the box.
5. turn the gearchange past 4th gear position using the handlebar. this should push the box off its studs. wiggle it to free the selector arm from the selector rod.
6. turn the box ‘upside down’ so you can see the innards. you can see the arm that engages the selector rod (that’s the thing sticking outta the engine case), and you can see where that arm is fastened to a cylindrical rod (connected up top to the notched wheel). @ the point where these two things are fastened, you should see a tapered pin connecting the two. if the pin is not thru both sides of the joint, hammer it in there. you could use a screwdriver as a drift. to really get at it, you will have to turn the box past 4th gear position by a fair distance.
7. now for the bad news… if it’s not one of the selector box problems, you probably have cruciform or gear problems. the cruciform is the next most likely cause, with a rounded cruciform skipping out of gear under load. if this continues for a long time, the gear surfaces can round off as well, thus destroying even a brand-new cruciform in no time. finally, loose gear shimming can create slop between gear and cruciform that can destroy BOTH.