Figure 3-40.Crankshaft construction.
The crankshaft, with the exception of the bearing
journals, is plated with alight coating of copper.
The bearing journals are case-hardened.
The bearing journals are ground to size.
Threads are cut into necessary bolt holes.
Crank throw arrangements for four-, six-, and eight-
cylinder engines are shown in figure 3-41. The
arrangements of throws determine the firing order of the
engine. The position of the throws for each cylinder
arrangement is paramount to the overall smoothness of
operation. For the various engine configurations,
typical throws are arranged as follows:
In-line four-cylinder engines have throws one
and four offset 180 degrees from throws two and
V-type engines have two cylinders operating off
each throw. The two end throws are on one plane
offset 180 degrees apart. The two center throws
are on another common plane, which is also 180
degrees apart. The two planes are offset 90
degrees from each other.
In-line six-cylinder engines have throws
a-ranged on three planes. There are two throws
on each plane that are in line with each other. The
three planes are arranged 120 degrees apart.
V-type twelve-cylinder engines have throw
arrangements like the in-line six-cylinder
engine. The difference is that each throw accepts
V-type six-cylinder engines have three throws at
120- degree intervals. Each throw accepts two-
The crankshaft is supported in the crankcase and
rotates in the main bearings (fig. 3-42). The connecting
rods are supported on the crankshaft by the rod
bearings. Crankshaft bearings are made as precision
inserts that consist of a hard shell of steel or bronze with
a thin lining of antifrictional metal or bearing alloy.
Bearings must be able to support the crankshaft rotation
and deliver power stroke thrust under the most adverse
The crankshaft rotates in the MAIN BEARINGS
located at both ends of the crankshaft and at certain
intermediate points. The upper halves of the bearing fit
right into the crankcase and the lower halves fit into the
caps that hold the crankshaft in place (fig. 3-43). These
bearings often are channeled for oil distribution and
may be lubricated with crankcase oil by pressure
through drilled passages or by splash. Some main
bearings have an integral thrust face that eliminates
crankshaft end play. To prevent the loss of oil, place the
seals at both ends of the crankshaft where it extends
through the crankcase.
When main bearings are
replaced, tighten the bearing cap to the proper tension
with a torque wrench and lock them in place with a
cotter pin or safety wire after they are in place.
VIBRATION DUE TO IMBALANCE is an
inherent problem with a crankshaft that is made with