If the surface is corroded or if the blades are damaged, replace the impeller

Water Pump Impeller Disassembly/Assembly
Water Pump Housing DisassemblyPiston Ring End Gap Inspection
Place the piston ring [A] inside the cylinder (upper
crankcase), using the piston to locate the ring squarely
in place. Set it close to the bottom of the cylinder, where
cylinder wear is low.
Measure the gap [B] between the ends of the ring with a
thickness gauge.
Piston Ring End Gap ...
KIBS Hydraulic Unit Installation
NOTICE
Brake fluid quickly ruins painted plastic surfaces;
any spilled fluid should be completely washed away
immediately.
Install the KIBS hydraulic unit together with the bracket.
Before installing the brake pipe, check to see that there is
no damage on the threads of the brake pipe joi ...
Clutch Plate Warp Inspection
Place each friction plate or steel plate on a surface plate
and measure the gap between the surface plate [A] and
each friction plate or steel plate [B] with a thickness gauge
[C]. The gap is the amount of friction or steel plate warp.
If any plate is warped over the service limit, repla ...