Boxerworks.com

So I’ve been putting together a 1975 r90/6 bobber build for the past 6 months or so. Just finally got it running proper. Took it out for a ride the other day, and it shifted smoothly through all the gears. Except it wouldn’t go into 5th gear.
When I pull the shifter lever up with my foot it doesn’t engage anything, and if I hold the shifter there and slowly release the clutch I can hear a faint clicking/ticking sound.

I jacked the bike up and dry shifted through the gears and I could shift it into 5th gear. But still would not go into 5th gear while riding.
I’m assuming the worst. But wanted to consult you all and see what you had to say.

Thanks in advance!

I'm sorry to be the bearer of bad news but there can be little doubt that there is a major fault in the gearbox. Either:

1)The teeth have all stripped on he mainshaft fifth gear or

2) The engagement dogs have broken off the same gear or

3) The fifth gear shifting fork is broken or

4) There is an off chance that it could be a fault with the shifting cam mechanism.

Whichever one of these turns out to be the fault, it will mean opening the box and replacing the busted bits... unless there as been collateral damage to other parts, in which case you're probably looking at a replacement box.

If you decide to repair the box yourself. and you've not worked on an airhead gearbox before, make sure you read up on procedures before you try to open it. There are special tools you'll need access to. In particular, removing the output flange requires a special puller and a lot of pressure. If the puller you use isn't man enough, it can let go with literally explosive force and there is a very real chance of serious injury.

Rob