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hydraulic Motor
Problem
A. Oil motor stalls at bottom (no
unusual heat problems)
B. Oil motor stalls at top (no
unusual heat problems)
C. Low pressure (okay on down
stroke, sluggish on up.stroke
— high heat)
NOTE: Engine labors on upstroke,
idles back at stall on the
down stroke.
D. Low pressure (both strokes -
high heat)
NOTE: Engine labors at stall on
both strokes.
cause
1. Fluid pump piston seat unthreaded
2. Valve sticking or oil motor trip rod shifter
assembly separated
1. Valve sticking
2. Broken spring retainer (valve rod
assembly)
3. Broken spring or valve rod
4. Air in hydraulic motor
5. Air in fluid pump
1. Blown piston seal
2. Cracked piston
1. Blown center o-rings on spool valve
2. Bad hydraulic pump
Solution
1. If connecting rod is okay, remove cylinder head
plug and pop valve down. Replace plug and start
machine. If machine cycles up and stops at bottom
again, then problem is piston seat on fluid pump.
Check piston seat. Repair or replace as necessary.
If piston seat is okay and problem does not change,
check oil motor.
2. Remove valve and check for scratches and rough
movement when sliding it up and down. Replace
valve and spool in this condition. Check trip rod
for possible separation.and spool in this condition.
Check trip rod for possible separation.
1. Remove valve and check for scratches and rough
movement when sliding it up and down. Replace
valve and spool in this condition.
2. Replace valve rod assembly.
3. Replace valve rod assembly.
4. Reset valve. Purge Air, generally accomplished by
low pressure cycling of motor/pump assembly for
5–10 minutes. Check for causes of air introduction:
• Loose fittings in tank.
• Loose fittings on hydraulic pump.
• Loose hose connections.
• Low oil in reservoir.
5. Stall at top can occur randomly when fluid pump
picks up air. Reset valve. Avoid air in the fluid pump.
1. Before dismantling oil motor, start machine. With
pump cycling under pressure, touch the hydraulic
cylinder and the head to see if cylinder or head gets
hotter. This will help determine if piston seal is blown
or piston nut is broken. If heat is on the head, check
the o-rings on spool valve.
2. Dismantle oil motor and check piston seals cylinder
bore and piston nut. Pay special attention to piston
nut. It can be cracked and not show externally.
1. Before dismantling oil motor, start machine. With
pump cycling under pressure, touch the head to see
if the head becomes hotter. This will help determine
if center o-ring is blown on spool valve. If hot, remove
and replace o-ring.
2. Replace hydraulic pump.
Troubleshooting
