Bush Hog 765H - Manual (Page 20)

Causes and Corrections, Continued
12. Bent piston rod in cylinder - replace or rebuild
the cylinder; replace damaged parts.
13. Worn or damaged rod seals on cylinder; external
leaks - repack cylinder. Rebuild cylinder,
replacing damaged parts as necessary.
14. Diverter valve on prime mover leaking externally
or bypassing oil internally through valve to
reservoir - diverter valve may need rebuilding or
replacing.
15. Something jamming the swing linkage - remove
interference.
16. Excessive back pressure - relieve condition. May
be restriction from outlet to reservoir.
17. Paint on valve spool; sticking valve spool or
scored valve spool - clean valve spool. Binding is
usually caused from an over tightened plug,
mounting bolt, fitting in valve body or tie rod bolt.
If a plug or fitting in the valve body is leaking, do
not over tighten in an effort to stop leak. This will
distort body casting and cause spools to bind.
Instead, the plug and fitting should be removed
from valve body and be reconnected, using a
new O-ring. Do not apply excessive pressure on
mounting bolts. The rods should be torqued to
20 ft./lbs. Never force spool, if binding occurs see
item 30 at the end.
18. Oil leakage past spool seal into spool cap -
remove cap. If it contains oil replace spool seal
O-rings. Check O-ring retainer to be sure it is
flat. If it has been “belled” check for restriction
from outlet to reservoir of valve which would
cause excessive back pressure. See item 30 at
the end and item 9.
19. Broken return springs - replace springs, see item
30 at the end and Figure 11.
20. Bent spool - replace with new spool section. See
item 30 at the end.
21. Foreign particles - clean system and valve.
22. Misalignment of control handle linkage - check
linkage for binding condition.
23. Spool not moved to full stroke - check travel,
should be 5/16” either way, or a total of 5/8”. See
item 30 at the end.
24. Relief valve setting in backhoe control valve too
low or defective - relief pressure will have to be
checked and corrections made. Backhoe system
pressure is 2100 psi for the 665H, 2100 psi for
the 765H, 2400 psi for the 865H and 2250 psi for
the 965H. Relief valve may need cleaning and
overhauling, or entire cartridge must be replaced.
See item 30 at the end.
25. Overload relief valve in the control valve stuck
open or malfunctioning - clean relief carefully but
do not disturb its pressure setting as it cannot be
field calibrated, or replace cartridge. See item 30
at the end.
26. Worn control valve - replace the control valve.
27. Check poppet in the control valve not holding -
clean check poppet(s) carefully, being sure that it
moves freely with good spring action and seats
properly or replace. See item 30 at the end.
28. Damaged or worn spool seals - replace spool
end seals, see item 30 at the end.
29. Ball in anti-cavitation check valve is stuck
or not seating properly - clean anti-cavitation
valve carefully, being sure that checks move
freely and seat properly, or replace cartridge. See
item 30 next.
30. Problems involving the control valve proper:
This valve is a precision device and is not intend-
ed for any extensive field adjustment or repair.
Field replacement parts are limited to seal kits,
cartridges, valve sections and tie rods.
Replacement of these parts, the opening of
check cavities and certain relief valve cavities to
examine for trapped dirt, or the resetting of the
main relief valve with the use of good pressure
gauge, should be referred to qualified service
personnel.
Dirt and shreds of packing material are the usual
causes of valve malfunction. Be sure the reser-
voir oil supply is kept clean and only factory sup-
plied packings are used in cylinder repair. Every-
thing must be clean and free of dirt during the
oil line removal and replacement, and during any
cylinder work.
Pages 19 and 20, Valve Repair-Disassembly,
explain the procedure to follow for valve repair.
The inclusion of this information and its use
does not imply that the warranty will remain
effective on the valve if it is tampered with
during the warranty period.
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