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CHANGING GEAR RATIOS
a/ With a drip tray placed beneath the gearbox, remove the drain plug (114) and drain the oil.
b/ Disconnect the reverse gear linkage from the gearbox.
c/ Remove the rear cover (36).
c/ Remove the M8 nuts (48) securing the bearing carrier (2), and slide it out of the maincase, complete with the gear cluster. It may
be necessary to tap lightly on the lugs provided to break the seal. Use a soft hammer for this purpose, never use a screwdriver to
lever between joint faces as this may damage the faces and impair the seal efficiency when reassembled. Take care not to drop
any of the pinion shaft components as they won't be fully supported at this time. The dummy shaft from SK-1451 can be used to
prevent the pinion shaft components from falling by inserting it into the rear end of the pinion shaft and sliding the loose parts
onto it.
d/ Remove the pinion gears (16), hubs (20), and clutch rings (19). Slide the input gears (46), and spacers (45) from the layshaft
(50), then withdraw the layshaft from the bearing carrier.
e/ Replace the gears with the required ratios. Gears are supplied in matched pairs, one for the mainshaft and one for the layshaft.
Each gear is marked with two sets of numbers. The first of these indicates the number of teeth on the layshaft gear, while the
second figure signifies the number of teeth on the mainshaft gear which mates with it. Both gears of each pair are marked in an
identical manner. It is essential that gears are correctly paired to these numbers.
Note: On all first gears, and some second gears, the gear teeth are machined integral with the layshaft. In such cases, therefore, if
a first (or second) gear ratio change is required, the layshaft itself must be changed.
f/ Whilst changing ratios it is advisable, as a matter of course, to wash and inspect all components which are to be used again
before refitting. Check for wear and cracks, particularly to the clutch rings. Also examine the selector forks for heavy or uneven
wear.
g/ Reassembly is the reverse of disassembly. Take care, when refitting the gear cluster into the maincase, to ensure location of the
layshaft into it's bearing, and of the selector barrel (15) it's driver (13). Assembly of the pinion shaft components is made easier
by use of the dummy shaft as described previously. [Some mechanics find assembly easier if the layshaft bearing inner track is
pre-fitted in the casing, rather than onto the end of the layshaft.]
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