JLG G6-42A Service Manual - Manual (Page 67)

3-29 G6-42A, G9-43A, G10-43A
Boom
3.11.3 Inspection Guidelines
Edge Wear
Check the chain for wear on the link plate edges
caused by running back and forth over the sheave.
The maximum reduction of material should not
exceed 5%. Measure and compare to a normal link
plate height by measuring a portion of chain that
does not run over the sheave. If the measured plate
height (1) is 5% less than the normal plate height
(2), discard and replace the chain.
Elongation
It is important to measure chain in section that
moves over sheaves because it receives most
frequent articulation. Measuring chain near its clevis
terminals could give an inaccurate reading. Ends of
chains, near clevis terminal, will not have flexed as
frequently, if at all, as the middle of chains.
It is best to measure in 12 pin increments from pin
center to pin center. For example, if links are one
inch from pin center to pin center, distance should be
12 in (305 mm). If links are 3/4 in (9,5 mm) apart,
distance after 12 pins should be 9 in (229 mm).
If distance measured (3) is 3% greater than normal
length (4), discard and replace chain.
Distorted or Battered Link Plates
Distorted or battered link plates (5) on a leaf chain can
cause tight joints and prevent flexing.
Turning or Protruding Pins
Highly loaded chain, operating with inadequate
lubrication can generate abnormal frictional forces
between pin and link plates. When chain is allowed
to operate in this condition, a pin or series of pins,
can begin to twist out of a chain, resulting in failure
.
Examine pin head rivets to determine if “VEE” flats
are still in correct alignment (6). Chain with rotated/
displaced heads (7) or abnormal pin protrusion (8)
should be replaced immediately.
DO NOT attempt to repair chain by welding or
driving pin(s) back into chain. Once the press fit
integrity between outside plates and pins has been
altered, it cannot be restored.
Any wear pattern on the pin heads or the sides of the
link plates indicates misalignment in the system.
This condition damages the chain as well as
increases frictional loading and should be corrected.
MZ1463
2 1
MY1360
3
4
8
MZ1466
5
MZ1465
6
7
8