BSA Owners' Club Forum

The BSA Workshop => Twins => Topic started by: Trev on 03 May, 2017, 11:16:15

Title: A10 gearbox problem
Post by: Trev on 03 May, 2017, 11:16:15
I have an intermittent gear selection problem. Sometimes changing up from 1st to 2nd the operation is stiff (not sure if that is the correct way to describe it)  when this happens there is no positive feel to it. The same thing happens when changing down to 2nd from 3rd. If I move the gear lever back to the central position then normally when I retry the gear engages perfectly. The return spring is OK as far as I can tell, and the gear lever returns to the central position as it should. This problem does not occur when changing up or down from 3rd to 4th and vice versa. This only seems to occur when the box has warmed up a bit, that is to say after I have ridden a few miles, I have not encountered this problem when the gearbox is still cold. This problem normally happens perhaps only once or twice during a ride, and often not all. The clutch is adjusted correctly as far as I am aware because I can easily select neutral while stationary from either 1st or 2nd. The gearbox oil level is correct. Can anyone offer any suggestions about what might be causing this problem? Incidentally, when the bike is on the centre stand I can select all gears with no problem and the gear lever seems to be operating correctly. One other thing that might be relevent that perhaps I should add. It never jumps out of gear.
Title: Re: A10 gearbox problem
Post by: royblackburn1@btinternet. on 04 May, 2017, 11:32:17
Hi Trev just read your problem when your bike is on the centre stand is the engine running? could it be your chain is too tight when the bike is not on the stand putting pressure on the gear box internals just a thought but might help Roy
Title: Re: A10 gearbox problem
Post by: Trev on 04 May, 2017, 13:03:17
Roy, thankyou for your response. No, the engine is not running when on the centre stand, I do however revolve the rear wheel in the direction of travel, and the chain is as far as I can tell, correctly adjusted. The way in which I adjust the chain is to check the tension with the bike off of the stand so that the weight of the bike is on the suspension. I do recognise what you are suggesting though, as whenever I have set the chain tension with the bike on the centre stand it always seems to be on the tight side. The problem is I know nothing about the workings of gearboxes, and therefore I am rather reluctant to start stripping it for examination. I really would not know what to look for. The sympton of what happens while changing between 1st and 2nd is not unlike that of the return spring being weak or having failed. I have rearsets so I have 1 down 3 up, and if I hook the pedal up after 2nd has failed to engage, it will then engage after doing this. All rather weird really.
Title: Re: A10 gearbox problem
Post by: Dean Southall on 04 May, 2017, 14:51:11
I had similar problems when the selector was misaligned by one notch. Very weird gear selection: sometime fine then I'd lose a gear and find find extra neutrals. Its seemed BSA's idea of red dot alignment and mine were at odds!
Sorry mate the only way to check this is to whip the end cover off the gearbox.
Title: Re: A10 gearbox problem
Post by: JulianS on 04 May, 2017, 15:06:34
The dots need to line up as in the photo, when box in neutral.

Also check the quadrant and the claw on gear selector for wear. Too worn and they wont engage properly and move the cam plate. Similar can happen if there is too much clearance between quadrant and claw when assembled, this can happen sometimes if there is too much loat on the gear change spindle and/or too thick a gasket used between inner and outer box covers.
Title: Re: A10 gearbox problem
Post by: Trev on 05 May, 2017, 10:12:36
Thanks everyone for all you input. More than a few things to think about there. I shall have to it seems, bite the bullet and take a look inside the box although I am not so sure that I am competent to make a clear diagnosis. Can I do this with the box in situ or will I have to remove it? One thing I have just remembered, is that the gear shift spindle has some movement, that is to say it has some slack, I can pull it in and out could this be an indicator of where the trouble lies? It occurs to me that maybe it needs to be shimmed to prevent this? or am I just clutching at straws?
Title: Re: A10 gearbox problem
Post by: JulianS on 05 May, 2017, 12:04:27
The spindle on my A10 has about 8 thou movement in and out. Shims between surfaces which have movement between them may break up. Shims usually used between surfaces with no relative movement. You could press the outer bush carefull inwards a little if you think the movement is too great.

You can check the indexing by just removing the outer cover.

You can dismantle the box leaving the main case in situ. You can leave the sprocket and rear chain attached.

Remove primary chaincase and clutch, the outer cover then release the single screw holding the inner cover and slide the inner cover out complete with the mainshaft and its fixed gear.

Just clean and examine everything carefully. You may find some wear to the layshaft bush in main case. Post photos and someone may be able to give an opinion as to condition.

The 2 layshaft gears which engage when second gear selected are shown in the photo. The lower gear in photo slides onto the fixed gear to engage.

Do you have a manual or factory service sheet coverig the gearbox?
Title: Re: A10 gearbox problem
Post by: Trev on 02 June, 2017, 14:19:18
Thanks everyone for all your comments, suggestions, and advice. Well, I thought better give you an update. I think that the problem is more or less resolved. It looks like the cam plate plunger was the source of the problem. There was 4 threads visible below the camplate lock nut, so I screwed the plunger up about one and a half turns. That seems to have done the trick. Oddly on the test ride when changing up from first to second it did stick a couple of times and then everything settled down and worked perfectly. I might just give it a small tweak, but as it appears to be functioning correctly now, I will leave it for now unless the problem returns. Not sure why raising the plunger should have had that effect but it has.