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[NicoV]

I had had serious shifting problems. I removed the entire gearbox, and put it back. Everything seems alright, and there is no excessive friction or anything blocking.
I seriously suspect the detent plunger. The housing of the plunger that screws into the cover, has some damage. I noticed the plunger has a groove. Why is that ? I suppose it cannot move freely around in its housing ? Mine does, probably due to the damage.
Also this: everything seems alright with the gearing and the bellcrank. Once I insert the detent plunger, and screw its bolt 1 mm into the gearbox, gear shifting is no longer possible. Do I replace the detent plunger and its bolt/housing with spring ?

[vince]

Hi, the detent should not rotate in its housing. The edge of which should be crimped into the grove for this purpose. As the assemble is screwed into the gearbox it should click, this shows its engaging with the selector. Vince

[Mark M]

Nico, I suggested that this might be the problem in your original post and advised that you check this before taking the rest of the gearbox apart. But you obviously decided not to do that! The detent plunger is often over adjusted by owners trying to fix gear selection problems. It's purpose is to give some positive location to the relative position of the gear change, it will not affect actual gear selection, that's what the adjustment in the outer case is for. As a result the plunger is sometimes broken by being screwed in too far. It cannot be repaired, it must be replaced as a unit but luckily it's cheap.

REgards, Mark

[NicoV]

I am now sure that the detent plunger has been modified by the previous owner with pincers, or maybe a vicegrip. He modified it in such a way that the plunger can rotate around freely.
I had ordered the gearbox overhaul kit, and will have a new plunger in a few days.
Well, Mark, I couldn't restrain myself from taking the gears out. I was just so curious. Amazingly easy. Putting them back was a bit trickier but it only took 20 minutes. Well, you were right. No problem in the gearbox whatsoever.
And what I now also know: the mileage on my bike is probably correct. I just see no signs of wear. Also the kickstart axle has no signs of wear.

[Mark M]

Nico, now you know how it works, good knowledge for the future! It's good news that the (initial) problem is so simple but do make sure you carefully follow the instructions when setting up the selector mechanism in the outer case. Previous Owners messing with the plunger is quite common, lots of folk think that screwing it in tighter will fix jumping out of gear problems and when it doesn't, go on to adjust something else thereby piling new problems top of the original one. Good luck with it!

REgards, Mark