Gearbox rebuild

[Gavin]

Can someone point me to a link (Utube or otherwise) that shows a step by step reassembling of a plunger gearbox please?

I am building one good box out of a few old ones, and not having done this before would like to be aware of the pitfalls. All that I have read so far assumes a lot of prior knowledge. All the utubes I have viewed scratch where it doesn't itch. Some do so for a very long time! There is one good one showing the challenges of installing the guts. But he suceeds by patience, trial, error and persistence. (A process known to many of us)

Thanks,

Gavin.

[Swarfcut]

 Gavin. If it's any help these boxes are simple compared to the majority of contemporary designs.

    Make sure you have the right parts. Plunger Layshaft has a plain shaft at the blind bush end, S/A shaft is the same dimensionally, but has a scroll here. They do interchange, providing you use the correct matching pair of layshaft pinion and layshaft third gear cog. The pinion drive dogs have a different profile, square v/s rounded, and the locating circlip position is  different.
  If changing mainshaft and layshaft pinions they are pressed on with a lot of force. Make sure any oil holes in the gears match corresponding oil holes in the layshaft. Position the sliding gears onto the shaft splines in a similar way so the oil holes can line up with the oilway in the layshaft centre.  Kickstart Quadrants must be used with their matching pinions, all previously detailed on the Forum as are the whole gamut of maladies folks have found.

  Layshaft endfloat is controlled by a hardened steel washer between the large first gear and the layshaft. This washer has a chamfer on the inner diameter. This faces the clutch, to clear the radius where the layshaft diameter is reduced.

 Easiest to assemble shafts, gears and selector arms into the box, leaving off the big first gear, then add the selector shaft rod. Leave the grubscrew 'til  the very last.

 BSA Service Sheet 209 gives you the basics.

 Swarfy.

[Gavin]

Thanks Swarfy,
I think between your info, Orabanda's similar sage advice, the Haynes A10 Owners Workshop Manual and service sheet 209 I'll have a ball in the shed for the next couple of weeks. Will be about another year before the bike it's to go in will hit the road whereupon I'll know if I've had a win.

[Jules]

On this topic, how do you check/know that the gearbox "works" once assembled on the bench ie gets all the gears and neutral please?
the last thing you want to do is wait until everything is assembled and try it out on a run!!

[Swarfcut]

 As a rough guide, the mainshaft should turn with uniform resistance (no tight bearings or bushes) and no clicks. Clicks come from the kickstart return spring rubbing on the ratchet pinion, more common on early boxes with the  flat clock spring where the initial fit on the splined kickstart shaft is less precise  and the spring has insufficient tension rather than the later  type coil spring hooked over the quadrant.

 Operating the kickstart drives the mainshaft and will allow upward changes to be made. Coming down the box the camplate plunger plays a more important part in positioning the camplate, too tight adjustment will cause the camplate to bind on the plunger, so if down changes are less precise, play with this adjustment.  Invert the box and add oil via the plunger location  just to lubricate the edge of the camplate, ( the plunger tip has to slide smoothly along the camplate edge) rather than filling the box normally,  in case assembly is incorrect and you have to start again.

 Turning the final drive sprocket at the same time will also help gears to change, easier done with an extra pair of hands.

 Swarfy.