In most diesel engines, the top bearing shell is removable with the top cap and the lower
shell is rolled out of or into position by the crankshaft. Unless bearings are at opposite ends of the
engine, they should be removed one at a time in order that the crankshaft may be held in position. The
shell should be rolled out of and into position with the same directional rotation of the crankshaft.
Crankshaft bearing failures often are caused by the shaft's misalinement or flexing. This
condition in turn can be traced to a low or misalined bearing resulting from a loose or distorted bearing
support or cracked engine frame. Bearing supports should be tight and in perfect alinement before a
shell is installed.
When checking the wear on a bearing, measure shell thickness with a micrometer at both
sides, at the bottom, and at any other points showing wear. If any number less than a complete set of
bearings is renewed, the shells applied must be scraped with a fine grit stone to within 0.001 inch of the
same thickness as the adjoining bearings or of the old shell. After the new shell is sized properly it
should roll into place freely. When installing a complete set of main bearings, roll a shell out from one
end of the engine and install a new one; then replace the shell at the opposite end of the engine. In this
manner the crankshaft is kept in place while intermediate bearings are being changed and less force is
necessary in rolling in the shells.
With all the shells in place and the caps tight, rotate the shaft by hand to make sure that it
is free. After the engine is reassembled, idle it under its own load for a few minutes in order to locate
any friction. Then stop the engine and remove one shell at a time and scrape if necessary. Continue this
operation until all shells show a good bearing.
c. Axle bearings. Typical axle bearing maintenance involves checking the oil depth: 1 3/4 inch
minimum, 3 1/2 inch maximum, measured on slant. Change any glazed packing, making sure that it is
packed tightly against windows and axle. Use a suction pump to take a sample of oil from the bottom of
the chamber and check it for water. If water is found, withdraw the oil and repack the bearings with
fresh packing. Bearings normally require repacking every 25,000 to 30,000 miles of service or every 6
months, whichever comes first.
To pack axle bearings, first empty and clean out the packing chamber. The axle caps are
fitted with a spring packing pusher; insert a wedge between the pusher and the axle to keep the spring