Lesson 1/Learning Event 1
FIGURE 28. CRANKSHAFT.
The crankshaft may well be called the backbone of the engine. It ties together the action of all the pistons--
changing their back and forth motion into rotary motion and carrying the power to the flywheel.
In addition to having many throws, the crankshaft has several machined bearing surfaces for mounting it in the
crankcase. Each mounting point in the crankcase is called a main bearing. The main bearings are made much
like the connecting rod bearings with removable caps and two-piece bearing inserts. One of the main bearings
has a lip or thrust surface on the sides of the bearing inserts. This is to control the end thrust or endwise
movement of the crankshaft. Oil seals are used at each end of the shaft, where it sticks out of the crankcase,
to prevent the leakage of lubricating oil.