I have my gearbox out, on the table, and attached to a stand. Outer cover is off, as is the inspection plate.

When last worked on, over 20 years ago, I had it completely apart, installed new bushings, bearings, rebuilt the shift mechanism, etc.

Rode it a bit and life interfered so the bike has been largely dormant until recently. Issues to be addressed is that it leaks when on the side stand, and does not shift well. Primary symptom of the latter issue is a false neutral between 2 & 3.

Having gotten a little smarter over the years, I decided to go slow and see what I could learn before just pulling it apart. I started with trying to adjust the shift mechanism to see if the false neutral could be eliminated. This brings me to my first questions, likely of many.

How much end play should there be in the gear control shaft? It sits in an open bushing on the timing side so can be easily measured. I get about 25 thousands of back and forth movement. Is this normal, or should shims be added? Would this contribute to spotty shifting?

There is no discernable end play in the main or lay shafts.

I note that there is a fair bit of slop in the shift mechanism pawls as they fit onto the shaft. Does adding some sort of shims there take any of that away and make the mechanism engage more consistently?

Finally (for the moment) has anyone ever found a really good step by step write up of making these things work as well as they can? I understand that they are a "slow box" requiring care when shifting, but am looking to improve my chances of good gearchanges up and down.

Thanks all, looking forward to getting this one back into riding shape.

Virtually no play is acceptabe on the shift shaft
And note that the position of the shims will either shift the mechanism towards 2nd & 4th or 1st & 3rd.
Adjusting the link rod will do the same thing,
To avaoid the false neutral you press down on the pedal hard & slow and hold it down till the clutch is back out
The root of the problems is the shape of the dogs which clash easily and tend to lock preventing the dogs to engage properly
BSA modified the box by changinf the shape of the dogs when the same box was used on the B range
The long dogs date back to the 20's when the metallurgy was nowhere near as good and they thought you needed a lot of cross sectional area to resist the dogs shearing off
WWII advanced steel metallurgy massively as wars tend to do so BSA realized that the original rectangualt dogs were over kill and caused poor slow shifting.
Remember that the box shifting mechanism actually dates back to 1914 hand change boxes.
There is an excellent write up in the technical section of the archives here and a long post over on BritIron I will pop a link to latter on
Right now I am doing the WM20 stuff, then I do the C series forum , the Gold Star forum, the tripple forum, the B50 forum the A forum then britiron & britbike so as McCarthur once said "I will be back "

Back as promised
https://www.britbike.com/forums/ubbthreads.php/topics/897545#Post897545
This is page 37 of a 50 page thread ( all 50 are worth reading ) but from here on Falco does the gearbox
https://www.britbike.com/forums/ubbthreads.php/topics/831490/37

I'm doing two gearboxes at the moment Joe, if I get time I'll try and write up a simple guide.
There does seem to be a lot of misunderstanding about how this gearboxes works (or doesn't)

Mark

email (option): pes.sales@btconnect.com

Thanks for the link Trevor.

I have read some of his stuff on BritBike, and am looking forward to spending time on that thread.

Thanks also for the word on the shaft end play. 25 thou seemed way to much. Time to pull things apart and see what is to be done.

Neale Gentner wrote a page in technical some years ago. It's still there. Scroll down to "Gearbox Tips" for the end float procedure.

http://www.wdbsa.nl/BSA%20M%20type%20gearbox.htm

Ron

email (option): ronpier@talk21.com

Charles is a physics professor so he can't help himself in going way OTT when it comes to measuring and perfecting .
So for him good enough does not exist thus his posts can get a tad overwhelming
HE also has a precision workshop that can work to 0.00005" tollerances which is substantially greater than the BSA competition shop worked to let alone the production lines.
I am about to attempt to replace the fixed with rolling pins that fit a lot tighter into the cam slots to pull some of the slop out of the changing but I need to do some lathe repairs first

This article on the gearbox by Neale Gentner I refer to regularly - if there was a method of pinning it to the forum it would be great - I always fail in the search mode

I find It’s well laid out & informative & clearly taken some time to put together - based on history & experience
It’s good to learn from such

I haven’t seen him on line now for some time which is a pity

I have built 2 gearboxes this year with this in mind & another document from Peter in Germany -
I have found very few issues in obtaining parts to rebuild them - with some of them being reproduced - but some of the smaller items like packing washers, shims & original control shaft roller pins are just not available or in a form you wouldn’t want to use
All made easier if you have access to engineering equipment which many of us don’t
It’s the least favourite item on my bike - the gearbox - I compare it always to my triumphs - I shouldn’t but - since I rebuilt my regular ride after Normandy - it’s a lot more enjoyable
Jo’b

email (option): jonnyob1@googlemail.com

I'm making tooling for 24-4235 and 24-4236. Should be ready in a week or so.
Does anyone have stock or a source for the little triangular section felt washer that pushes up to the nose of the sleeve gear over the mainshaft?

Mark

email (option): pes.sales@btconnect.com

Hi mark
I have both felts required
The chamfered main sleeve / clutch felt
Pushrod felt

Both are nos - the smaller one was impossible to find
I had to buy a box of them

Drop me a line if required
Br
Job

email (option): jonnyob1@googlemail.com

Does anyone know of a source, or substitute for the packing washers needed to adjust the end plan on the gear control shaft? 66-3086 and 66-3087.

The internals of my box look very good. Plan is to install the sealed main bearing and attempt to remove some of the play in the control shaft, but with what? I did find a possible source for 66-3086 in Australia, but not sure if the seller would be willing to ship such a small order to the US.

Hi joe
Going from memory - no shims were used on the control shaft on wartime boxes - but this was revised after the war to provide shims behind the control shaft bush in the main shell - 66-3084

I have failed to find these 66-3086 washers - it’s painful to shim the shaft as you need to remove the bush each time to check / although I think it acceptable to place it or another suitable shim on the outside temporarily - between the shaft & bush - to obtain clearance

Something maybe mark could machine for us ?

66-3087 is also a post war addition - not a Wd box part - but one I suspect the wartime box could do with

I would gladly buy from down under if original was available
Br
Jo’b

email (option): jonnyob1@googlemail.com

My bike is a 53, civilian model. Supposedly.

I say supposedly, as the engine number begins with WM20 and could be from an earlier year. It has not been bored, based on no oversize marking on the piston.

Assuming the gearbox is from 1953, the packing washers were used, as needed (I guess)

Be glad to hear from anyone who has used a shim internal to the bush. It looks like it has a thrust face, which may explain why the shim is behind it. Putting a shim in front of a thrust point would make me concerned that it could be torn loose with evil results.

I bought the mainshaft shims from Les at Russell's. They are NOS 5 thou in boxes of 12. Ron

email (option): ronpier@talk21.com

Hi joe
Shim on outside for purpose of shimming only but - I know gearboxes on bikes where they were left on outside between the bush & control shaft - still working away - but best behind

Main shaft shims are available in 5 thou as ron highlighted - there were 10 thou in times past but no longer easily obtainable- but you can double them up or use as required

Br
Job

email (option): jonnyob1@googlemail.com

[....I have both felts required. The chamfered main sleeve clutch felt / Pushrod felt..]

I never use either of these felts with no apparent derimental effect...I've done 10's of thousands of miles with that set up....Ian

email (option): ian@wright52.plus.com

email (option): pes.sales@btconnect.com