DETROIT DIESEL 53
Connecting Rod 1.6.2
CONNECTING ROD BEARINGS
Bearing failures may result from deterioration (acid
The connecting rod bearing shells are of the replaceable
formation) or contamination of the oil or loss of oil which
precision type and consist of an upper shell seated in
results in scratching, etching, scoring or excessive wear.
the connecting rod and a lower shell seated in the
An analysis of the lubricating oil may be required to
connecting rod cap (Fig. 2, Section 1.6.1). The bearing
determine if corrosive acid and sulfur are present which
shells are located by and prevented from end wise or
cause acid etching, flaking and pitting. Bearing seizure
radial movement by a tang at the parting line at one end
may be due to low oil or no lubricating oil.
of each shell. The connecting rod bearing shells used in
the engines incorporate a relief groove in each end of
Check the oil filter elements for heavy sludge deposits.
the shell to provide clearance for the connecting rod
If necessary, replace the elements.
bolts.
After removal, clean the bearings and inspect them for
The connecting rod bearing caps are numbered
scoring, pitting, flaking, etching and dirt grooving. If any
1R, 1L, 2R, 2L, etc. on
of these defects are present, the bearings must be
the V-type engine, with matching numbers stamped on
discarded.
However, babbitt plated bearings may
the connecting rod. Each bearing cap (and bearing
develop minute cracks or small isolated cavities on the
shell) must be installed on its original connecting rod.
bearing surface during engine operation. These are
characteristics of and are NOT detrimental to this type
Since the upper and lower connecting rod bearing shells
of bearing. The bearings should not be replaced for
are different, they must not be interchanged. The upper
these minor surface imperfections. The upper bearing
bearing shell has two short oil grooves and two oil holes;
shells, which carry the load, will normally show signs of
each groove begins at the end of the shell and
distress before the lower shells do.
terminates at an oil hole. The lower bearing shell has a
continuous oil groove from one end of the shell to the
Inspect the back of the bearing shells for bright spots
other. These grooves maintain registry with the oil holes
which indicate they have been moving in their supports.
in the crankshaft journals, thereby providing a constant
If such spots are present, discard the bearing shells.
supply of lubricating oil to the connecting rod bearings
Also inspect the connecting rod bearing bores for burrs,
and to the piston pin bushings and spray nozzle through
foreign particles, etc.
the oil passage in the connecting rod.
Measure the thickness of the bearing shells at point "C",
Remove Bearing Shells from Connecting Rod
90 from the parting line, as shown in Fig. 6, Section
(Connecting Rod, Piston and Liner in Place)
1.3.4. Use a micrometer and ball attachment J 4757 as
illustrated in Fig. 7, Section 1.3.4.
1. Drain the engine lubricating oil.
The minimum thickness of a worn standard bearing shell
should not be less than .123". In addition to this
2. Remove the oil pan.
thickness measurement, check the clearance between
3. Disconnect and remove the oil pump inlet tube
the connecting rod bearing shells and the crankshaft
assembly.
journal. This clearance may be checked with the
crankshaft in place by squeezing a soft plastic
4. Remove one connecting rod bearing cap. Push the
measuring strip between the crankshaft journal and the
connecting rod and piston assembly up into the cylinder
bearing shells (see Shop Note in Section 1.0).
liner far enough to permit removal of the upper bearing
shell. Do not pound on the edge of the shell with a
One connecting rod bearing shell should not be
sharp tool.
replaced. If one bearing shell requires replacement,
both the upper and lower shells should be replaced.
5. Inspect the upper and lower bearing shells as
outlined under Inspection.
Inspect the crankshaft journals, as outlined in Section
1.3, for wear before replacement bearings are installed.
6. Install the bearing shells and bearing cap before
another cap is removed.
Bearing shells in .010", .020" and .030" undersize are
available for service with crankshafts which have worn
Inspection
or have been ground to a smaller journal diameter
Visual
inspection,
as
well
as
dimensional
measurements, should be made to determine whether
the used bearings are satisfactory for further service or
must
be
replaced.
1970 General Motors Corp.
July, 1970
SEC 1.6.2 Page 1
