User Manual

200 BENCH PROCEDURES
Page 5-7
During initial production, part numbers were
stamped onto the through hole of the connecting
rod bearing cap. In later production, the part
number was forged into the I-beam of the rod.
Old-style connecting rods (without alignment
sleeves) and new-style connecting rods (with
alignment sleeves) may be intermixed in an
engine. However, the capscrews and alignment
sleeves are not interchangeable between the two
rod assemblies. The alignment sleeves will
physically fit into either of the connecting rod
assemblies, but the sleeve must be used in the
new-style 367GC4267M or M2 connecting rods
ONLY. The capscrews cannot be mixed. The
difference in the thread size between the two
rod assemblies is significant enough that the
14-mm threaded capscrews will not even engage
the 16-mm tapped hole in the old-style
(367GC4255M or M2) rod assemblies. The
16-mm threaded capscrew cannot be assembled
into the 14-mm tapped hole of the new-style
(367GC4267M or M2) connecting rod
assemblies.
It is essential to closely control the weight of
reciprocating parts. MACK E7 connecting rods
fall into two weight classes. Prior to mid-1996
production, the weight classes are identified by
an “M” number (M1 or M2) stamped onto the
connecting rod bearing cap. Effective with mid-
1996 production, the M2 connecting rod is no
longer stamped with this weight designation. The
M1 weight class rod will continue to be stamped
on the rod cap. When installing a single rod, or
less than a full set, examine removed rod for part
number and M number. Installing parts with the
same weight class is preferred.
Connecting rods can be weighed to ensure using
proper weight class. Connecting rod weights
for each engine, within each weight class, should
not vary by more than 0.46 ounce (13.04 grams).
The maximum weight difference between the
heaviest possible M2 rod and the lightest
possible M1 rod is 0.83 ounce (23.53 grams).
Special Tools Required
앫 Piston Pin Bushing Remover/Installer
J 37717
앫 Piston Pin Burnishing Broach J 37718
앫 Connecting Rod Fixture 945-6041
Inspection
앫 Inspect connecting rods for nicks, cracks,
signs of overheating, bends or twisting that
can cause rod failure.
앫 Inspect bolt holes for elongation or pulled
threads.
앫 Check mating surfaces between rod and cap
for correct fit.
앫 Inspect the crankshaft journal bearing
surface and wrist pin bushing.
If any of the above parts are suspected of being
faulty, replace the connecting rod.
If it is determined that the condition of any part or
component is questionable or is at the limit of
tolerance, throw it out; it may fail or become out of
tolerance after a short time in operation. It is cost-
efficient to replace components when rebuilding.
Always use genuine MACK replacement parts.
Wrist Pin Repair
WRIST PIN BUSHING REMOVAL
If the wrist pin bushing is found to be out of
tolerance, it should be replaced.
Refer to Figure 5-4.
To replace bushing:
1. Position rod in a press with piston pin
bushing remover/installer J 37717 inserted
into wrist pin bushing.
2. Press bushing out of rod.
5-101.bk Page 7 Friday, March 17, 2006 11:05 AM