TM 5-3810-300-24&P-3
1.6.2
CONNECTING ROD BEARINGS
The connecting rod bearing shells (Fig. I) are precision
NOTE: If shims are used between the oil pump
made and are replaceable without shim adjustments.
body and the main bearing caps, save the
They consist of an upper bearing shell seated in the
shims
so they may be reinstalled when
connecting rod and a lower bearing shell seated in the
installing the oil pump.
connecting rod cap. The bearing shells are prevented
from endwise or radial movement by a tang at the parting
3. Remove one connecting rod bearing cap. Push the
line at one end of each bearing shell.
piston and rod assembly up into the cylinder liner far
enough to permit removal of the upper bearing shell. Do
Various types of bearings have been used. Currently,
not pound on the edge of the bearing shell with a sharp
multiple layer copper-lead coplated or aluminum triplated
tool.
bearings are in use. These bearings have an inner
surface, called the matrix, of copper-lead or aluminum.
4. Inspect the upper and lower bearing shells as
A thin deposit of babbitt is then plated onto the matrix.
outlined under Inspection.
This babbitt overlay has excellent resistance to friction,
corrosion and scoring tendencies which, combined with
5. Install the bearing shells and bearing cap before
the material of the matrix, provides improved load
another connecting rod bearing cap is removed.
carrying characteristics. These bearings are identified by
the satin silver sheen of the babbitt when new and a dull
Inspection
gray after being in service. The former copper-lead
bearings had a copper color when new and turned very
Bearing failures may result from deterioration (acid
dark during engine operation.
formation) or contamination of the oil or loss of oil. An
analysis of the lubricating oil may be required to
The upper and lower connecting rod bearing shells are
determine if corrosive acid and sulphur are present
different and are not interchangeable.
The upper
which cause acid etching, flaking and pitting. Bearing
bearing shell is grooved midway between the bearing
seizure may be due to low oil or no oil.
edges, part way up from each parting line, with an oil
hole through the shell at the termination of each groove.
The lower bearing shell has a continuous oil groove,
extending from one parting line to the other, in line with
that of the upper bearing shell. These grooves maintain
a continuous registry with the oil hole in the crankshaft
connecting rod journal, thereby providing a constant
supply of lubricating oil to the connecting rod bearings,
piston pin bushings and spray nozzle through the oil
passage in the connecting rod.
Remove Bearing Shells
The connecting rod bearing caps are numbered 1, 2, 3,
etc., with matching numbers stamped on the connecting
rods. When removed, each bearing cap and the bearing
shells must always be reinstalled on the original
connecting rod.
Remove the connecting rod bearings as follows:
1. Drain the oil and remove the oil pan.
2. Remove the lubricating oil pump and the pump inlet
and outlet pipes.
Fig. 1 - Connecting Rod and Bearing Shells
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