BSA Pre-Unit 4 Speed GearBox

For theoretical Maximum Speed in the Gears download this .xls Worksheet


The Gearbox:
Kick Start, Gearshift & Clutch




outercover.jpg (65877 bytes)
Kick + gearshift + oil level plug + oil filling + clutch shaft + clutch adjustement + speedodrive.

Impressive & very well made piece of machinery. 7 functions in one place!


innercover2.jpg (84010 bytes)
Inner cover, gives access to one of the mainshaft bearing. Renewed it while I had the opportunity. Heated the aluminium cover in boiling water then easily drove in the new bearing, cold after some hours in the freezer. This procedure always made renewing bearings an easy task.



innercover1.jpg (81705 bytes)
Inner cover with gear"claw". This is the old plunger box, swingarm\newer A10'a have a different selecting\pedal return mechanism. Have no complaints with this box, shifting is fine, no problem finding neutral.


kick&gearshaft.jpg (59195 bytes)
Gearchange & kick shafts. Look like they will last forever and then some... Added shims to take up some slight slack that had developped over the (50) years.



gearshafts.jpg (91293 bytes)
Removing outer covers permits some inspection of the sprockets & selector mechanism etc

without removing it from the bike. The clutch rod goes trough the mainshaft, check it for straightness.


kickratchet.jpg (56611 bytes)
The kick ratchet system. Wear is apparent, when too worn the kick will slip and\or jam.


kickspring.jpg (93405 bytes)
A broken kick return spring.

So brittle with age it just broke. New fitted.


kick.jpg (42495 bytes)
Rebuilding, locking the kick with the clutchlever. Careful not to scratch the outer cover with the inside of the kick, insert a piece of something between kick & cover (see picture). Check clutchshaft for excessive play as there is no bush, it goes directly trough the aluminium casting which is subject to wear.