JLG 1850SJ Service Manual - Manual (Page 268)

SECTION 5 - BASIC HYDRAULIC INFORMATION & HYDRAULIC SCHEMATICS
5-98 – JLG Lift – 3121619
CYLINDER BLOCK
Examine cylinder block running face. Surface should be
smooth and free of nicks and burrs. Ensure no scratches or
grooves exist; these may drastically reduce output flow.
CONTROL
1. Examine PC and LS plugs for signs of wear. Check small
tip of plugs for heavy wear and replace if necessary.
2. Inspect spool springs to make sure they are intact.
Check inside and outside surfaces of springs for wear
and replace if necessary.
3. Check spool's outside diameter for scratches and burrs.
Clean and coat all spools, bores, and seals with a light
coating of hydraulic oil.
INPUT SHAFT
1. Check shaft and splines are straight and free of damage
or heavy wear. Inspect shaft surface where it meets shaft
seal. Replace shaft if a groove exists at sealing land sur-
face that may let dirt into or hydraulic fluid out of unit.
2. Clean sealing area with a nonabrasive material if neces-
sary. Lubricate shaft with a light coat of hydraulic fluid.
SWASH PLATE
1. Inspect each surface of swash plate for wear. All swash
plate surfaces should be smooth. Inspect swash plate's
slipper running surface for damage and brass transfer.
Excessive brass transfer from slippers may indicate they
should be replaced.
2. Check swash plate bearing journal for scratches. Replace
swash plate if necessary
JO U RNAL BEARINGS
Inspect journal bearings for damage or excessive wear.
Replace journal bearings if scratched, warped, or excessively
worn. Polymer wear layer must be smooth and intact.
V ALV E P L ATE
1. Inspect valve plate for scratches and grooves. Check for
evidence of any cavitation along the running face. If pit-
ting from cavitation exists, replace valve plate.
2. Check for excess wear on brass running face. If any dis-
coloration or burn marks are observed, replace valve
plate.
3. Run a fingernail or pencil tip across diameter of sealing
land surface. Deep or outstanding grooves may
decrease pump flow. Lap or replace if grooves or nicks
are present. Inspect mating surfaces of end cap and
valve plate for contamination; even a few thousandths
of an inch may affect pump operation.
4. Measure thickness of valve plate. Ensure valve plate par-
allelism is equal to or less than 0.001 in (0.025 mm).
Appearance should be flat and smooth running face and
bottom surface.
5. Valve plate should be flat to 0.0002 in (0.005 mm) con-
vex. A magnetic particle inspection is recommended to
detect cracks. Valve plate must be replaced if any cracks
exist.
Maximum bore diameter
0.785 in (19.8 mm)
Minimum Cylinder
Block Height
2.45 in (62.25 mm)
Flat to 0.000079 in
(0.002 mm)
Figure 5-128. Cylinder Block Wear Measurements
0.153 in (3.88 mm ) Min
(0.025 mm)
0.001 in
0.0002 in
(0.005 mm)
Convex Max
Figure 5-129. Valve Plate Wear Measurements