SERVICE MANUAL
CONNECTING RODS, PISTONS, RINGS & SLEEVES
Section 5
GENERAL
CONNECTING RODS are forged of high-grade steel.
The rod has a bearing at each end. The upper bearing is
a bushing-type used at the piston pin, which anchors it to
the piston. The bearing at the crankshaft end of the rod
(lower end) is a two-piece bearing that fits around the
crankshaft journal and is secured by a bearing cap. The
rod and bearing caps are mated parts with definite
markings on both the cap and rod which prevent
mismatching as shown in Fig. 2.
Figure 2. - Connecting Rod and Cap Identification
Numbers
1.
Mated Surface I.D. Numbers
Currently the 300 Series uses a 35
split line connecting
rod and cap assembly (672116C91) with tang in rod and
slots in cap.
The 400 Series uses two connecting rod assemblies:
1.
The old 35
split line connecting rod and cap
assembly (684294C91 and 685012C91) with slot
and tang in rod and cap.
2.
The new 45
split line connecting rod and cap
assembly (688923C91) with tang in rods and
slots in cap. The new rod and cap assembly
have a revised piston pin, oil reservoir and bolts.
NOTE: Old and new connecting rods can be
intermixed for engines In the field. New connecting
rod bolts (6 766 79C2) can be used in the old
connecting rod assemblies but old bolts (676679C1)
must not be used In new connecting rod assemblies.
The PISTONS are cast aluminum alloy, which are cam
ground and weight controlled. Each piston is fitted with
two COMPRESSION RINGS and one OIL CONTROL
RING.
Atomized fuel is injected into a dish-shaped recess in the
dome of the piston by the injection nozzle valve. The
force of combustion pressure is transmitted by the piston
and connecting rod to the crankshaft. The escape of
combustion pressure past the piston is prevented by the
piston rings. The fit of the piston and rings in the sleeve
must be close enough to prevent the escape of
combustion gases, yet free enough to keep friction to its
working minimum.
The 300 Series and early 400 Series engines are
equipped with a crankcase mounted ventilation system
which utilizes conventional pistons and piston rings. Late
model 400 Series engines have the new valve cover
mounted crankcase ventilation system.
These used "BALANCE-PRESSURE" pistons with a
revised second land configuration (Fig. 3) and top ring
groove. A new "INTERMEDIATE PISTON RING" (Fig.
4) was also released with an increased ring gap
specification.
Cutback Land Piston
All 400 Series Turbocharged engines use pistons
incorporating the cutback land design [Refer to Fig. 3].
Cutback refers to the pistons smaller diameter above the
top ring groove compared to the diameter below the top
ring. The passageway created by the smaller diameter
allows combustion gas pressure to reach the top piston
ring.
CGES-185-3
PRINTED IN UNITED STATES OF AMERICA
Page 2
