Motor - Kubota U20-3 Workshop Manual

U20-3, U25-3 WSM
d. Motor
Problem
No pressure rise or no oil flow.
Oil viscosity inappropriate.
Motor failure
Dust, degraded hydraulic oil, cavitation,
to run
internal parts seized due to excessive radial
load, unusual contact, bearing damaged.
Incoming flowrate too low.
Rpm not as
Low viscosity and internal leak for oil
designed
temperature or other reason.
Internal parts worn out.
Wrong pipe connections.
Wrong
turning
Poor valve timing due to wrong
direction
disassembling/reassembling procedures.
Oil seal scratched or worn.
Loose bolt or plug, resulting in oil leak (at
joints) from O-ring.
Oil leak O-ring scratched or damaged.
Dust or dent on the O-ring contact face.
Cracked port, damaged screw.
Inappropriate joint.
Shaft poorly fitted.
Air left in the circuit or motor.
Unusual
noise
Pump's cavitation.
Air mixed in the suction pipe line.
Unusual Cooler in trouble.
temperature
Motor seized.
rise
As listed above, there are various problems and their possible causes. The majority of troubles are,
however, caused by the entry of dust. Be very attentive not to allow any dust into the system.
Cause
Check the entire hydraulic circuit including the valves and pumps.
Ensure the specified viscosity ranges.
Run the motor alone and get it under a pressure of 30 kgf/cm
MPa) or so. If it fails to run, then some internal parts might be seized
or damaged. Disassemble the motor and replace damaged parts.
Check the pump discharge rate, the motor rpm, and the valves for oil
leak.
Ensure the specified viscosity ranges.
Replace worn-out parts.
Reverse the pipe connections.
Disassemble and reassemble again for good valve timing.
Replace the oil seal. Repair or replace if the shaft seal contact
surface is scratched or worn.
Tighten the bolt and plug to their specified torques. See also if the O-
ring is damaged. Replace the O-ring as required.
Replace the O-ring.
Check for hit marks, burr, etc. Correct the surface with #600 or so
sandpaper. Replace the O-ring. Clean up and reassemble.
Replace the housing. Use an appropriate joint and tighten it to the
specified torque.
Center the shaft exactly.
Let out the air completely. Fill the motor with oil and keep it running
under no load until there is no air bubbles in the tank.
Unclog the suction filter.
Apply oil or grease to each connection and carefully listen to the noise
there. If the noise is less, retighten the joint there.
Repair the cooler.
Repair or replacement
IV-S-7
Hydraulic system (Service section)
Correction
2
(2.9