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Assembly sequence for 4 speed gearbox

This is a picture fig1 of how the gear cluster all fits together when finised and instaled in the engine.
Note the difference, and which way around the two selector forks are fitted
also note that mine are missing the rollers that should be fitted to the pins.

Fig1a is exploded diagram of gearbox internals

Assemble only the gears and selector forks as in this picture in the RH crankcase fig2

Fit selector quadrant index ball and spring in case fig3

Check selector quadrant is aligned like this fig4 then bolt into case
This is the only tricky bit you have to move the selector forks up/down so they engage with the quadrant without knocking the rollers off the forks. I also turn the quadrant so that 2nd gear stop will engage with the indent ball.
Then you have to press down on the quadrant against the index ball/spring pressure to fit the two securing bolts,
be very careful you do not cross thread the bolts. Also note that the Tab washers are not fitted in this picture, make sure you fit these and lock them. fig5

Fit layshaft
Fit gear selector shaft fig 6and fig7

Points to note on Engine reassembly

If you are replacing the Main crank bearings make sure that they are a sliding fit on the crankshaft, like the originals before fitting into crankcases.

once they are fitted before fitting the crank oil seals or the gears back in the case. now is the time to check end-float on crank the crank endfloat should not be less the .004th to allow for heat expansion, BSA state 004--006 acceptable limit.

Hope this page was helpful, any questions, feedback re errors typos etc can be sent to P5XBX at