TM 5-6115-400-35
inches when installed and with bearing
Raising the bore .003 inch-.004 inch at the
caps properly torqued.
flywheel end of the engine can be
tolerated if the bore is made straight and
(2) The bearing shells are prevented from
the front main bore is not repositioned.
radial movement by a dowel pin in the
When installing a replacement cap, make
bearing cap which locates the lower half
certain the casting or part number on the
of the bearing shell and in turn prevents
cap is in the same relative position as the
the upper bearing shell from radial
number on the old cap when installed.
movement. The halves of the bearing
(2) After the bearing cap has been machined,
shells are identical, therefore, they may
the dowel for locating the bearing shell,
be installed in either the upper or lower
must be pressed into the cap. Press
positions.
dowel in far enough so that top of dowel is
b. Removal.
flush with the bottom of the bearing shell
(1) Remove the crankshaft (refer to para 60).
oil groove when shell is positioned in the
(2) Remove the main bearing upper shells
cap.
from their seats in the cylinder block.
(3) If a main bearing burns out with enough
(3) Remove the main bearing lower shells
heat to cause distortion at one or more of
from their seats in the main bearing caps.
the main bearing bores or saddles,
Note.
generally the block and bearing caps will
Identify bearing shells as to their
pull in at their joint causing an oblong
original location in the cylinder block
bore. If the flat areas, where the cap
and main bearing caps in the event
contacts the block around the main
inspection proves they can be
bearing attaching capscrews, have
reused.
distorted so they are no longer flat and
straight, the area will have to be hand
c. Inspection.
filed and fitted to the replacement bearing
(1) Any bearing shells that are scored,
cap so that when the new cap is installed
chipped, pitted, or worn beyond the
it will not be distorted from being pulled
specified limits given below must be
down on an out-of-square surface. A thin
replaced. Inspect backs of the shells for
coat of Prussian Blue can be used on the
bright spots. Bright spots on backs of the
new cap to detect any out-of-squareness
shells indicate shells have shifted in their
at this point.
supports and are unfit for further use.
59. Main Bearings
Note.
a. General.
The specified clearance between
main bearing shells and the
(1) The main bearings are of the precision
type and are replaceable without
crankshaft journals is .0021 inch -
machining.
The front and rear main
.0048 inch. New bearing shells must
bearings are 1.995 inch-2.005 inch long;
be installed when this clearance
the four intermediate main bearings are
exceeds .009 inch.
1.495 inch-1.505 inch long; and the center
(2) With crankshaft removed, measure inside
main bearings are 2.746 inch-2.756 inch
diameter of the bearing at a point 900
long. The center main bearing includes
from the parting line, with bearing cap
four thrust flanges and four dowel pins
installed and tightened to the specified
which prevent the flanges from moving
torque. Bearing shells when in place are
radially. All the main bearings have an
.002 inch larger in diameter at the parting
inside diameter of 8.9981 inches-3.9998
line
129
