I wonder if anyone out there can give me some advice?
I'm trying to find a sprocket to fit a vintage BSA gearbox which I'm sure would have the same arrangement as the M20 box.
Can anyone tell me if I'm looking for a sprocket with a boss long enough to tighten hard up against the outer sealing disc and inner bearing race leaving a gap between the sprocket face and the end of the splines for the lockwasher to locate. Or is there a gap between the sprocket boss and the bearing, because I see that the sleeve gear splines are tapered, indicating they should be locked together. If there is a gap, then the sealing disc would be free to rattle about in it's recess, which can't be right.
I'm probably over thinking this, but I see that if I fit a sprocket with a short boss, the sprocket locks up hard on the tapered splines, but the end of the sprocket splines are flush with the face of the sprocket, so the lockwasher will not locate. When I assemble it with the bearing, the splines are sunken allowing me to fit the lockwasher. So this means that in this condition, the splines are not quite locking on the tapers.
My own thoughts are that when everything was new, the tapers locked hard and the sprocket boss locked hard against the bearing when the ring nut was tightened.
Sorry if I've made your head hurt here. If I had an M20 gear box in front of me, I could answer my own question, and obviously, if you have all the correct parts, you simply assemble them without much thought.
Can anyone advise?
What year and model BSA?
As for a tapered spline sleeve gear, never seen such a thing. With the gear locked on the taper, how would ever be be able to remove the gear and how would it be pulled against the bearing??
A photo and more info about what bike you have would help.
Well, it's a 4 speed Sloper/J11 gearbox, but I'm sure the design of the sleeve gear/sprocket is the same as the M20.
Taper is perhaps not the right word, but if you look closely, the splines on the sleeve gear are ramped and taper off at the end, so as I say, if the sprocket is fitted without the bearing, the parallel sprocket splines lock up against the ramped splines on the gear. Maybe the M20 has parallel splines for their whole length.....I don't know.
So my question is, do the splines do the locking or is it the boss being hard against the bearing? Maybe a bit of both?
The "ramped splines" on the sleeve gear are the result of the machining process as it was most likely done on a horizontal mill with a big round milling cutter. It has nothing to do with a "lock fit" as the sprocket should never touch this area of the sleeve gear. All sleeve gears look like this (Triumph, BSA Norton...etc.) and it has nothing to do with "locking" the sprocket on to the sleeve gear.
The sprocket needs to slide on the sleeve gear until it contacts the bearing and the nut will lock it all together.
If you have the original sprocket, you need to turn off the teeth in a lathe and weld a new one on. Unless someone make sloper sprockets?
The BSA J11 is a 500cc V twin I think? A really nice bike!!!!
Steve,
I have both gearboxes here on the bench (the J11 with the "open air" gear change)
It looks like the J11 sprocket measures 18,3 mm wide. And is tight to the ring on the main bearing.
And the M20 sprocket is 18 mm wide.
Apart from that its all the same.
Hopefully this is of some help.
Bruce, Thank you so much for your advice. This is exactly what I wanted to know. You are a very knowledgeable fellow.
Mike, Thanks for your input. Yes, the M20 sprocket I have is about 18mm, but the boss is too short for the box I have. The one that fits nicely is more like 28mm. I think the 4 speed Sloper box is the same as the 1934 J11, with the "open air" gearchange. However, I've just noticed the sleeve gears are different, so this would account for the difference in width.
Anyhow, I'm all set now for reassembly, apart from knowing how to check the layshaft endfloat. I managed it on an M20 gearbox with a rig holding a lever type DTI, but the layshaft on the Sloper box is lower down, and it won't reach.
What a wonderful Forum this is.
Many aftermarket sprockets are not always the best made.
With a M20 sprocket the splines do not extend to the end to give clearance on the spline ramps.
The ramps are left by the nature of the tool that cut them.
I was hoping to have new M20 sprockets made by now, but machine issues have delayed production.
Mark
email (option): pes.sales@pesltd.uk
Thanks for that, Mark.
It's a pity I can't spell Gerabox.
The sloper sprocket is a different bore, also sloper use a 3/8” chain not 5/16”.
The sleeve gear is not the same as M20
Thanks Darren. Yes, the 3 speed Sloper has a smaller bore, but the M20 sprocket fits the 4 speed sleeve gear nicely, although they are different sleeve gears, they have the same splines. So it should be possible to have an M20 sprocket retoothed to 3/8. I will have to make a spacer for the sprocket, as the M20 has a shorter boss.