C15S SCRAMBLER GEAR SELECTION

[Spaceman]

Hi
Really appreciate your help.
Will have a go soon. One last silly question to make it sure for me, when you say LH and RH which direction are looking at the gearbox.

Looking towards the front of the bike. LH end means the end closest to the clutch; RH end means closest to the kickstarter.

[bobby12]

Hi
Thanks will have a look.
Going to have ago at fitting tomorrow.
One last question, the quadrant part has two prongs and four slots in the corresponding plate, when setting the cam plate like you've explained which two slots out of the four should these prongs be in ?

[Spaceman]

Surprisingly, in neutral, the two quadrant plungers rest on the camplate itself below and above the lower two slots. In 1st gear, the upper plunger sits in the 2nd slot up but the lower plunger still rests on the camplate below the lower slot. In 2nd gear, the plungers fit inside the bottom slot and the third slot from the bottom.

[bobby12]

Hi
Thanks for the update, will have a look tomorrow, thought a British bike would be less complicated than a Jab but maybe not 🤞😭

[Spaceman]

All 4-speed gearboxes have to do a similar job. However, it definitely gets more complicated when you have 5 or more gears which requires 3 rather than 2 selector forks to try to hook up to a selector drum!

[bobby12]

Hi,
Up date on my gearbox problems.
Have had the gearbox in and out a few times now, without any success.
All the parts have been checked and all are in very good working condition lots being new parts.
They are all fitted in the correct positions, the problem seems to be with the quadrant body assembly,
it is working by hand  with new springs, the two plungers work, but when the box is assembled and fitted this quadrant part does not seem to want to engage and disengage properly but I cannot see why, there is a little play in the shaft body hole. Sometimes you can engage a gear but not very often. The cam plate is also new and fitted correctly.
Anyone had similar issues or any more comments would be appreciated, not sure what else to check.

[Spaceman]

Could you explain exactly what happens if you start in neutral and then try to change up or down? What should happen is that one of the plungers should initially drop into one of the camplate cut outs after which exerting pressure on the gear lever should allow the plunger to push the camplate up or down until it indexes the gear. So the question is whether you can see the movement of the camplate by looking at its exposed end or are the quadrant plungers definitely not engaging with the camplate?

[bobby12]

Hi
With just the cam plate and quadrant in place and no gears I can turn the cam plate through all the positions going forward or backwards.when all the gears are in place the quadrant plungers seem to stock at various positions. I will have another good look and try looking at what day Saturday.

[Spaceman]

It sounds as though the gear change mechanism is working correctly with the selector forks removed allowing the camplate to index correctly for all the gears?

Have you tried to exercise the gear change mechanism with everything assembled outside the gearbox on the outer timing cover? I've never tried to do this in this way but, if possible, could give you a better understanding of what is going wrong? 

[bobby12]

Hi
A frustrated up-date.
Have completely stripped down all gearbox parts again, checked and then re -assembled.
The whole unit does feel better, I can engage all the gears without the selector forks in place when these are fitted I can select some gears, feelsa bit hit and miss, when I re-fit the wholes gear box I can sort of get gears but they are not smooth, perhaps I am expecting it to feel like a Jap box ? Wondering when its fitted with oil, clutch and engine running maybe it will behave differently ?

[Spaceman]

The only criterion is to be able to reliably select all the the gears in turn (up and down) rotating the shafts when necessary to allow the dogs on the sliding pinions to slide into the cut outs in the adjacent pinions. It's never going to feel smooth doing it without engine running and with no oil in the gearbox!

[bobby12]

Hi
Gear selection not really sorted but what I'm going to do is complete the engine rebuild and fit back into the frame and see with the rear wheel and chain fitted if there is any difference
One thing I have noticed is that I thought all BSA gear selection was 1 up and 3 down. I have the cam fitted correctly to the service sheets and manual etc but mine is 1 down and 3 up, is this normal perhaps for a Scrambler?

[Spaceman]

1 down and 3 up is the way it normally works on most bikes including BSA bikes as this is the most intuitive arrangement. I would definitely get the gearbox working with the engine out of the frame - it won't be any easier once it's fitted.

[DAVE BRADY]

Hi,

A10s and those using the same gear box and I think other pre-unit gearboxes are 1 up and 3 down.

Dave.

[Spaceman]

I'd forgotten most pre-unit BSA bikes used the 'race pattern' 1 up / 3 down gearbox shift pattern in contrast with the equivalent Triumph pre-unit bikes that all used normal 1 down / 3 up. The reason BSA went this way may have had something to do with patents rather than trying to make their customers think they were buying race bikes!