9-22. MAIN BEARINGS REPLACEMENT.
General. Main bearings consist of two shells, an upper and lower. Only the upper shells of the main bearing
have oil holes and therefore, are not interchangeable. Care must be taken during installation that the main
bearing shell containing the oil hole is installed in the cylinder block. If a main bearing shell without an oil hole is
inadvertently installed in the cylinder block, lubricating oil will be prevented from reaching the bearing shell. This
will result in burned bearing shells and a severely damaged crankshaft. If the main bearing shells are
serviceable, replace them in the same main bearing bores from which they were removed. To avoid nicks,
scratches, and contamination, keep the handling of bearing shells to a minimum.
Inspection. Inspection of main bearing shells is accomplished during the replacement procedure in accordance
with step d, below.
To avoid crankshaft or bearing damage, each main bearing shell must be removed and
Installed before proceeding to the next bearing shell. Start at No.1 bearing shell, and match-
mark the bearing caps to the cylinder block If necessary.
Remove the main bearing side-lock capscrews (14, Figure 9-24) and lockwashers (15) from both sides of cylinder
Remove the capscrews (16) and washers (17) securing the main bearing cap (1 8) to the cylinder block (58).
Using main bearing cap puller ST-1116 or a small pry bar, remove the main bearing cap (18).
Remove the lower main bearing shell (19 or 20) from the cap (18) and, if damaged, remove the dowel (21).
Fabricate a removal tool in accordance with Figure 9-33.
Install the removal tool in the lubrication hole in the crankshaft (32, Figure 9-24) and rotate the crankshaft so the
flat of the removal tool contacts the edge of the bearing shell (22 or 23) opposite the tang on the bearing shell
(Figure 9-33). Rotate the crankshaft to remove the bearing shell.
Dry cleaning solvent PD-680, Type Ill, or equivalent, is flammable and moderately toxic to the
skin, eyes, and respiratory tract. Assure adequate ventilation. Skin, eye, and respiratory
protection is required to avoid Injury to personnel.
Being careful not to mix or interchange the bearing shells (19, 20, 22, and 23). Clean each bearing shell in
filtered solvent PD-680, Type II, or equivalent, and dry carefully.
Visually inspect each bearing shell for defects and signs of uneven wear. Interpret bearing shell
appearance as follows:
Bearing shells that have been operating at the correct clearance and with adequate lubrication, will
have a dull gray color. Bearing shells having a black surface, or showing varnish build-up, have
been running at excessive clearance and shall be replaced.
Bearing shells that show bright shiny spots or areas, have been running at insufficient clearance and
shall be replaced. If the bright areas appear along one edge of the bearing shell, misalignment
exists. Check the main bearing bores for alignment in accordance with paragraph 9-31.
Bearing shells that are flaked, scored, galled, or show visible, embedded dirt particles shall be