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 TM 9-8000
operation. For the various engine configurations, typical
throws are arranged as follows:
(1) In-line four-cylinder engines have throws one
and four offset 180 degrees from throws two and three.
(2) V-type engines have two cylinders operating off of
each throw. The two end throws are on one plane offset
180 degrees apart. The two center throws are on another
common plane. They are also offset 180 degrees apart.
The two planes are offset 90 degrees from each other.
(3) In-line six-cylinder engines have their throws
arranged 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.
(4) V-type 12-cylinder engines have throw
arrangements like the in-line six-cylinder engines. The
difference is that each throw accepts two-engine
cylinders.
(5) V-type six-cylinder engines have three throws at
Figure 3-30. Piston Pin.
120-degree intervals. Each throw accepts two-engine
(3) The crankshaft, with the exception of the bearing
cylinders.
journals, is plated with a light coating of copper.
d. Crankshaft Vibration. A crankshaft is very prone to
(4) The bearing journals are case- hardened.
vibration because of its shape, extreme weight, and the
tremendous forces acting on it. The following are three
(5) The bearing journals are ground to size.
basic areas that are of concern when considering
vibration in crankshaft design.
(6) Threads are cut into necessary bolt holes.
c. Throw Arrangements (Fig. 3-35). The arrangement
problem with a crankshaft is
of the throws on the crankshaft determines the firing
order of the engine. The position of the throws for each
cylinder arrangement is paramount to the overall
smoothness
of
Figure 3-31. Piston Pin Construction
3-18
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