C15S SCRAMBLER GEAR SELECTION

[bobby12]

Hi
First BSA to own, quick question, I have the engine on my work bench, should I be able to engage all gears whilst in this position by turning the gear sprocket ?
Thanks,

[Beesy]

Yes you should, it was a bit fiddly on my B25, it sometimes needed a good yank on the gear lever

[Spaceman]

You haven't got much leverage using the engine sprocket - if you can hold the engine steady, it might be easier to run through the gears using the kickstart lever.

[bobby12]

Hi
Thanks for your help. The engine was rebuilt couple years ago by previous owner, lots of new parts, still struggling to select any gears except first and neutral. Engine on bench minus clutch etc, looks like I might have to remove inner cover with gears and selector to have look, seems not too bad but don't like removing gearboxes, any tips or pit falls doing the job ?

[Spaceman]

It's an easy job especially with the clutch removed because all the gearbox innards should come away with the inner timing cover when you remove it.

However, it would be interesting to know what happens when you try to change up from neutral. For example, do you get full travel on the gear lever but nothing happens and it makes no sounds even when you try to rotate the gears with the kickstarter?

[bobby12]

Hi
From neutral I can click up a gear, back down to neutral but then cannot seem to be able to engage any other gears below just  fresh  air., no click or engagement of any gears.

[Spaceman]

For whatever reason, it sounds as though the gear change quadrant is not able to rotate the camplate as it should - normally, when the camplate is moved by the gear lever via the quadrant, it slots into the next detent position and at the same time moves the pinions via the selector forks to set up the next gear. The problem could be as simple as a broken detent spring. However, it should be obvious what the problem is after you withdraw the innards attached to the inner timing cover.

[bobby12]

Hi
Many thanks for your help and advice.
I will remove gear cluster and take a look.
When the cluster is out should I be able to fit the gear lever and try to select the gears at this stage ?

[Spaceman]

You should be able to exercise all the gears with a bit of manual help with everything on the bench but bear in mind it will all be a bit floppy because the LH end of everything will not be supported; and there will be no detent spring to define each detent position of the camplate. Hopefully, you will see the problem straightaway when you pull out the innards - there's only a small number of things that could possibly be wrong with it.

[bobby12]

Hi
Removed the cluster and good / bad news for me.
When removing the cluster a couple of gears, washer and a selector fork fell out , not sure if this is normal.
So, I cannot see why the gears will not engage, all parts seem to be there and I checked with the parts manual that all the gears, washers etc are all present and the correct ones.
I will now try to assemble all correctly and see what happens, the main problem I can see is I am not sure what position the the cam plate and quadrant should be in when assembling, where the the selector forks go, if that makes sense. Will read up and see if the service sheets give any info.

[Spaceman]

You need to position the gearbox in neutral. If you look at the LH end of the camplate you will see 5 notches which are the detent positions in the four gears and neutral. The neutral notch is the second from the bottom and basically the two selector fork rollers should be in line with this notch for the gearbox to be in neutral. The RH (outer) selector fork engages with the outer camplate slot and goes down to the layshaft sliding gear. The LH (inner) selector fork engages with the far slot and goes up to the mainshaft sliding gear.

[bobby12]

Many thanks, I will try and fit, going to clean inside and what I can get at first whilst the cluster is out .Fingers crossed 🤞I removed the nut and kickstart parts from the shaft before sliding the cluster out should I have left this intact and if so it would be better to connect before sliding cluster back

[Spaceman]

It's best to assemble everything on the inner timing cover first and check against the parts diagram especially that you've got the shim on the RH end of the layshaft and the washer on the LH end of the mainshaft. I assume the detent spring bolted to the LH wall of the gearbox is ok?

[bobby12]

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.

[Beesy]

Have a look at this. Not the same bike but principle is the same.

https://youtu.be/SrZTENzk55g

The tricky part is knowing if the reason it won't go fully home is because something isn't right or you're simply not pushing hard enough against the spring at the far end of the gearbox, but a bit of wiggling and jiggling should sort it out.

That channel has some other useful unit construction tips