TM 5-3810-300-24-&P-3
1.6.2
Connecting Rod Bearings
Bearing shells are available in .010", .020"and .030 "
Bearing
*New Bearing
Minimum
undersize for service with reground crankshafts. To
Size
Thickness
Worn Thickness
determine the size bearings required, refer to Crankshaft
standard
.1548"/.1553"
.1530"
undersize are available to compensate for slight journal
.002" Undersize
.1558"/.1563"
.1540"
wear where it is unnecessary to regrind the crankshaft.
.010" Undersize
.1598"/.1603"
.1580"
.020" Undersize
.1648"/.1653"
.1630"
CAUTION: Bearing shells are NOT reworkable
from one undersize to another under any
.030" Undersize
.1698"/.1703"
.1680"
circumstances.
*Thickness 90 from parting line of bearing.
Install Connecting Rod Bearing Shells
After removal, clean the bearings and inspect them for
scoring, pitting, flaking, chipping, cracking, loss of babbitt
With the crankshaft and the piston and connecting rod
or signs of overheating. If any of these defects are
assembly in place, install the connecting rod bearings as
present, the bearings must be discarded. However,
follows:
babbitt plated bearings may develop minute cracks or
small isolated cavities on the bearing surface during
1. Rotate the crankshaft until the connecting rod journal
engine operation. These are characteristics of and are
is at the bottom of its travel, then wipe the journal clean
NOT detrimental to this type of bearing. The bearings
and lubricate it with clean engine oil.
should not be replaced for these minor surface
2. Install the upper bearing shell--the one with the
imperfections. The upper bearing shells, which carry the
short groove and oil hole at each parting line--in the
load, will normally show signs of distress before the
connecting rod. Be sure the tang on the bearing shell fits
lower bearing shells do.
in the groove in the connecting rod.
Inspect the backs of the bearing shells for bright spots
3. Pull the piston and rod assembly down until the
which indicate they have been shifting in their supports.
upper rod bearing seats firmly on the crankshaft journal.
If such spots are present, discard the bearing shells.
Also inspect the connecting rod bearing bore for burrs,
4. Note the numbers stamped on the connecting rod
foreign particles, etc.
and the bearing cap and install the lower bearing shell --
the one with the continuous oil groove--in the bearing
Measure the thickness of the bearing shells, using a
cap, with the tang on the bearing shell in the groove in
micrometer and ball attachment J 4757, as described
the bearing cap.
The minimum
thickness of a worn standard connecting rod bearing
5. Install the bearing and cap and tighten the
shell should not be less than .1530" and, if either bearing
connecting rod bolt nuts to 60-70 lb-ft (81-95 Nrn) torque
shell is thinner than this dimension, replace both bearing
(lubrite nut) or 65-75 lb-ft (88-102 Nm) torque
shells. A new standard bearing shell has a thickness of
(castellated nut).
.1548 " to .1553". Refer to Table 1.
6. Install the lubricating oil pump and the oil inlet and
In addition to the thickness' measurement, check the
outlet pipes.
clearance between the connecting rod bearing shells and
NOTE: If shims were used between the oil
the crankshaft journal. This clearance may be checked
pump body and the main bearing caps, install
by means of a soft plastic measuring strip which is
the shims in exactly the same location from
squeezed between the journal and the bearing (refer to
which they were removed.
rod bearing-to-journal clearance with used parts is .006".
7. Install the oil pan, using a new gasket.
Before installing the bearings, inspect the crankshaft
8. Refer to the Lubricating Oil Specifications in Section
13.3 and fill the crankcase to the proper level on the
dipstick.
Do not replace one connecting rod bearing shell alone. If
one bearing shell requires replacement, install both new
If new bearings were installed, operate the engine on the
upper and lower bearing shells. Also, if a new or
reground crankshaft is to be used, install all new bearing
shells.
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