JLG G6-42A Service Manual - Manual (Page 42)

Boom
3-4 G6-42A, G9-43A, G10-43A
3.2 BOOM SYSTEM - THREE SECTION
3.2.1 Boom System Operation
The three section boom consists of the first, second and
third assemblies with a single extend chain, and a single
retract chain.
As the extend/retract cylinder, which is anchored at the
rear of the first boom section, and the front of the push
beam begins to extend, it forces the second and third
boom sections out of the first boom section.
The boom sections are connected by extend and retract
chains. These chains are routed around sheaves on the
front of the push beam and the rear of the second boom
section. As the extend/retract cylinder is forced out
hydraulically, the second boom section is pulled out by
the push beam, and third boom section is pulled out by
the extend chain.
As hydraulic pressure is applied to the retract port on the
extend/retract cylinder, the retract chain pulls the third
boom section and the push beam pulls the second boom
section back into the first boom section.
The mechanical linkage formed by the chains and
supporting hardware, extend and retracts the second and
third boom sections at the same rate.
The boom section lifts and lowers via action of the lift/
lower cylinder.
3.3 BOOM ASSEMBLY MAINTENANCE
These instructions provide the complete boom assembly
removal and installation or the second and third boom
sections removal and installation.
Before beginning, conduct a visual inspection of the
machine and work area, and review the task about to be
undertaken. Read, understand and follow these
instructions.The boom assembly consists of the first,
second and third section booms and supporting
hardware.
Note: Before removing the boom or boom section, the
carriage or any other attachment must be removed from
the quick coupler.
Before beginning, conduct a visual inspection of the
machine and work area, and review the task about to be
undertaken. Read, understand and follow these
instructions.
During service of the boom, perform the following:
1. Check wear pads. (Refer to Section 3.11, “Boom
Wear Pads.”)
2. Check hose sheaves and chain rollers.
3. Apply grease at all lubrication points (grease fittings).
(Refer to Section 2.6, “Lubrication Schedules.”)
4. Check for proper operation by operating all boom
functions through their full ranges of motion several
times.
Note: Depending on your particular circumstance, the
following procedures explain the removal/installation of
individual boom sections or removal/installation of the
complete boom
.
WARNING
NEVER weld or drill the boom unless approved in
writing by the manufacturer. The structural integrity of
the boom will be impaired if subjected to any repair
involving welding or drilling.