gearbox nuances

[DAVE BRADY]

A funny thing happened to me on the way to the Forum.

I have been sorting out a gearbox for my A65.  I am using '71 cases that I had without any fittings so a rummage through the box of gear box stuff and the best parts are selected and assembled.  Shafts, gears, selectors, selector plate, cover plate etc.
All checked and cleaned.  Most parts are quite good but they are all the best that I have.
One tip is to swap the sliding gears between shafts so that almost unused 'dogs' are used so this was done,  reduce the length of the plunger spring to make gear change a bit lighter - did this. Got the end float of the layshaft down to a minimum.  All new bearings.  Once assembled on the cover plate everything looks good and works. So get it in the cases and tick it off as done. Yes! No!.  The cluster slid easily into the cases but the cam plate would not move, I could not get the gears to change.  What have I done wrong?  Take it out check it all.  Make sure everything fits together well and everything moves smoothly - yes it does.
Maybe it is the plunger that holds the cam plate in place. I had fitted a new one with a ball on the end - it must be this.
It moves smoothly in its location but take it out and put a standard one in - that will sort it.  No it won't.
By the time I realised what the problem was I could strip and reassemble the cluster like a well trained commando could strip and clean his semi-automatic rifle.
I must admit I was at my wits end.  I have the bike on a lift made from a hospital bed but as I am 6'1'' it is still low for me so I was always looking down towards the gearbox.  For some reason I looked right in to the cases and suddenly saw the problem.  A curved mark bore witness to what I was about to realise.
BSA have always changed things, some times subtly and some times not.  Gear boxes and in particular the gear change cam plate are such a change.
Early ones are plain and were found to be a bit weak.  The next ones had a reinforcing bit welded on and the final ones were made thicker and without a reinforcing bit as they did not need it.  But guess what I discovered?  They subtly changed the cases.
To accommodate the reinforcing bit the case was machined with a nicely curved flat bit.  Obviously this incurred a cost so when the slightly thicker one was introduced they no longer did this machining.
I have '71 cases and '69/'70 gear cluster so they do not go together without modification.
So to finish this rather long post, I got the dremel out and made a flat bit so the reinforcing bit did not jam on the case any longer.  The cluster is now in and ready for final tightening.  Gear box done, blood pressure down and stress relieved through this post.
Thanks for reading it.

Dave.

[Mike Farmer]

 

Hi Dave.

That is a seriously good explanation. Bril

Glad you are upsides with it now

Take care

Mike