Before I strip the gearbox fully and with the kickstart mechanism removed. What is the acceptable end float on the gearbox main shaft? I have 0.052" Looking at the shim thickness variants in Rupert Ratio's book and assuming I have thrust washers in place, how can this be reduced?
Bike in question is a 1968 B441Shooting Star
I assume you have measured this end float with the nut removed from the RH end? In practice, with the nut done up, there will be no end float since the mainshaft will then be locked to the RH bearing. In practice, I think all you can do is to use the thickest available spacer that will fit purely, as RR says, to minimise the effect on the gearbox of the mainshaft nut coming undone or the gearbox sprocket nut coming undone - both of which being highly unlikely.
Correct, but on page 95 second paragraph of (RR) and I quote
'The aim here is to take up clearance between the mainshaft splines and the sleeve gear to achieve just perceptible end float of the mainshaft'
Well, I continued to dismantle the gearbox and all Thrust Washers are in place. So looking at the mainshaft thrust washers that are installed in my box, the most that I could reduce the end float is by 0.024" if I replace them with the largest available. Therefore I will still have nearly 30 thou end float, is that perceptible?
This is not really end float as such because the mainshaft is locked to the RH bearing and so will not 'float'. The real issue, I believe, is that you will get slightly more movement of the 2nd gear pinion as it engages with the sleeve gear but, to be honest, I can't see an extra movement of 24 thou causing any great issue.
I think your right and maybe I'm just believing that perceptible end float is a couple of thou. But my gearbox with 52 thou additional float for the Mainshaft 2nd gear is making life difficult to select 2nd gear as well as destroying the layshaft selector fork roller, twice and the layshaft 3rd gear Dogs. I've been looking for any abnormalities.
I need to think about the problem a bit more but what you are referring to as an extra 24 thou of end float should not affect 2nd gear selection as this does not involve the mainshaft 2nd gear pinion locking into the sleeve gear which is where the extra clearance would be. From what you have said, the problem may be with the layshaft rather than the mainshaft.
I have rebuilt my fair share of BSA unit singles but have never measured this mainshaft 'end float' previously since it is not end float in the real sense and it is difficult to see how it could lead to a problem inside the gearbox. However, having said that, if you have the largest spacer (not a thrust washer), 40-3127, which is 0.103/4" thick and you still need another 24 thou of spacer thickness then something is not quite right. Assuming someone hasn't used a gasket between the crankcase and the inner timing cover, I would definitely check the mainshaft RH bearing is properly seated and its circlip is in place.
It sounds as though you have had quite a big problem in using the gearbox and you are now looking for a cause? If the gearbox issues are with 2nd and 3rd gear then that would point to the issue being with the RHS of the gearbox and not at the spacer end. I would definitely say it is more likely to be related to the layshaft and its pinion movement as you change gear. The first thing I would do is to check the end float of the layshaft using the procedure outlined in RR.
It might simply be that your problems stem from an issue with the gearchange mechanism itself involving the quadrant, camplate and selector forks. Unfortunately, it can take an experienced eye to spot this sort of problem but it is sometimes it is worth assembling everything onto the inner timing cover so that you can see what is happening as you change gear.
Spaceman, thank you very much, it's good to get another enthusiasts input.
Having had 5 Unit Singles myself, this is the first gearbox problem I've had that's not staring me in the face. I think that the box has been abused, which is not unusual for a B44 especially if it's been used off road. It's an American import, so I have little or no history and it was in poor mechanical condition. So far as I know the gear cluster, apart from the layshft 3rd is original and so is the gear selection parts apart from a new cam plate and return spring.
I have the latest selector plate to fit, new springs for the quadrant plungers and I'm looking for another layshaft selector fork. The existing fork is badly worn.
The bike is a 1968 B441 Shooting Star, which I built just before Lock-Down and it's been stored since 2020 and now after a lengthy period of getting her starting reliably, it will not select 2nd gear with the engine running. It finds 1st, 3rd and top going up or down cleanly and she pulls like a train. No problem on the stand stationary all gears select with hand winding the rear wheel.
If I change out the thrust washer next to the mainshaft 3rd, what's the best way to remove both the 1st & 3rd Pinion from the mainshft?
As you probably know, the M/S has one sliding pinion (2nd gear) operated by one selector fork and the L/S has a sliding pinion (3rd gear) operated by the other selector fork. Neutral is selected with both sliding pinions not engaging or being locked into either neighbouring pinion.
If you look at the gearbox schematics in RR Vol 1, you will see that 1st and 2nd gears do not involve the M/S siding pinion moving into engagement with a neighbour. 1st gear involves the L/S sliding pinion moving to the right to lock into the 1st gear pinion. 2nd gear involves the L/S sliding pinion to the left to lock with the neighbouring 2nd gear pinion. 3rd gear involves the L/S sliding pinion to move to the neutral position and for the M/S sliding pinion to move to the right to lock with the 3rd gear pinion. 4th gear also involves the L/S sliding pinion being in the neutral position and the M/S sliding pinion moving to the left to lock with the 4th gear pinion.
All a bit complicated but, if you can't select 2nd gear, this all means that the L/S sliding pinion is the problem and is not able to be moved to the left to lock with the 2nd gear pinion. If you look at the camplate diagram, you will see that it is the elbow in the L/S slot (furthest from camplate spring) that is responsible for moving the L/S sliding pinion to the left to engage 2nd gear.
I assume the gear clusters are ok and that you can manually move the sliding pinions to engage with either neighbour and there is nothing stopping the L/S sliding pinion moving to the left to engage with the 2nd gear pinion? If so, I would have thought the problem is with the camplate or the L/S selector fork. If you assemble everything onto the inner timing cover, you should be able to exercise the gears and see what is going wrong with 2nd gear?
Hi Spaceman,
Great observation. Since then I've checked the all of the selector assembly and I'm trying to source the parts. Obviously it being Easter I'll have to wait until next week to make contact and hopefully acquire every thing and then I can check them in the Inner cover.
I'll post the outcome, hopefully it will be positive. Have a good weekend and Thank you :)
Managed to squire another Layshaft selector fork and spindle from RR, through the BSAOC. Managed to get her running and went for a test ride, bingo all gears working up and down, sorted.
Now to get her starting easier, but it's a B44🥴