JLG G12-55A AccuPlace Service Manual - Manual (Page 32)

Boom
3.10 G10-55A & G12-55A AccuPlace
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 the chain in the section
that moves over the sheaves because it receives the
most frequent articulation. Measuring the chain near
its clevis terminals could give an inaccurate reading.
The ends of the chains, near the clevis terminal, will
not have flexed as frequently, if at all, as the middle
of the chains.
It is best to measure in 12 pin increments from pin
center to pin center. For example, if the links are one
inch from pin center to pin center, the distance
should be 12 in (305 mm). If the links are 3/4 in
apart, the distance after 12 pins should be 9 in.
If the distance measured (3) is 3% greater than the
normal length (4), discard and replace the 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 the pin head rivets to determine if the
“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 the chain by welding or
driving the pin(s) back into the 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