TM 5-2420-230-24-2
Bearings, Main (001-006)
B3.9 and B5.9 Series Engines
Page 1-12
Section 1 - Cylinder Block - Group 01
Operate the engine to normal operating temperature, and
check for leaks.
Bearings, Main (001-006)
General Information
The crankshaft is a balanced, forged steel unit. Four-
cylinder engines have five main bearings. Six-cylinder en-
gines have seven main bearings. The lower bearing shells
are all the same. All of the upper bearing shells are also the
same with the exception of the journal adjacent to the rear
one. The next to last journal is fitted with a flanged upper
bearing shell. The flanges control the end thrust of the
crankshaft.
The upper bearings have three holes in them. The middle
hole receives lubricating oil from the main oil rifle. One of
the adjacent holes is aligned with a drilling in the camshaft
journal and serves as an orifice for lubrication flow to the
journal. The other adjacent hole supplies lubricating oil for
piston cooling. The hole does not align perfectly with the
cooling nozzle. The hole is offset to keep it away from the
highly loaded bearing area.
NOTE: Oversize service main bearings are available for
reground crankshafts.
L-690
