If a master cylinder or piston shows any damage, replace them.

If a cup is worn, damaged softened (rotted), or swollen, the piston assembly should be replaced to renew the cups.
If fluid leakage is noted at the brake lever, the piston assembly should be replaced to renew the cups.
If they are damaged, replace them.
If the springs are damaged, replace them.
If the relief port becomes plugged, the brake pads will drag on the disc. Blow the ports clean with compressed air.
Front Master Cylinder [I] Rear Master Cylinder [J]

Rear Master Cylinder Installation
Brake DiscChain Slack Adjustment
Remove the cotter pin, and loosen
the axle nut.
Loosen the left and right chain adjuster
locknuts.
A. Axle Nut
B. Cotter Pin
C. Adjuster
D. Locknut
If the chain is too loose, turn out the
left and right chain adjusters evenly.
If the chain is too tight, turn in the left
...
Transmission Assy Installation
Assemble the transmission assy (see Transmission Assy
Assembly).
Be sure that the dowel pins are in position.
Install the transmission assy on the crankcase.
Tighten:
Torque - Transmission Case Bolts: 20 N·m (2.0 kgf·m, 15
ft·lb)
Install:
Shift Shaft (see External Shift Mechani ...
Thermostat Installation
Replace the O-rings [A] with new ones, and apply grease
to them.
Assemble:
O-rings
Thermostat Housing [B]
Thermostat [C]
Thermostat Cap [D]
Install the thermostat [A] in the housing so that the air
bleeder hole [B] is on top.
Tighten:
Torque - Thermostat Cap Bolts: 5.9 N ...