LO 8-11 Identify and describe the purpose, function, and types of diesel engine flywheels

1. Flywheels

Flywheels

Flywheels are like large plates bolted to the rear of the engine, and they serve several purposes. Their primary purpose is to provide some inertia between power impulses to keep the engine rotating. Storing energy in the heavy flywheel produced during each power impulse and releasing it when the engine speed slows down helps to smooth out engine speed. A toothed ring gear, fastened to the circumference of the flywheel, provides a drive point for the starting motor pinion gear. To crank the engine, the starter will engage the engine through the flywheel ring gear. Starter ring gears are usually friction fitted; this means they are first heated and placed over the circumference of the flywheel before they contract. Using an electric welding machine, a bead of filler material is applied to the flywheel and ring gear in several places to assure adhesion to the flywheel when ring gears are replaced in the field.

Behind the flywheel is the rear main bearing seal (also called the rear seal ). The rear seal prevents crankcase oil from leaking into the flywheel housing. Turning tools are often temporarily attached to the flywheel to rotate the engine when performing service procedures Figure 71.

A flywheel also provides a mounting surface for a clutch in the case of a manual transmission and a torque converter for automatic transmissions. The heavier mass of the torque converter requires only a thinner and lighter flywheel (called a flexplate ) to connect to the engine Figure 72. Flywheel shape and construction can vary depending on the type of clutch used and whether torsional damping capabilities are built into the flywheel.

On the flywheels of many engines are scribed markings, letters or numbers that are used as reference points to adjust valves or install fuel injection components. For this reason, the flywheel must be precisely lined up with the correct engine position corresponding to markings on the flywheel. Flywheel bolt holes may be offset to ensure that the flywheel is installed in the correct position. A dowel pin may also be used to properly locate a flywheel to align the centerline of the flywheel with the crankshaft Figure 73.

FIGURE 08-71: The turning tool attached to the bell housing of this Detroit DD15 is used to rotate the engine during service procedures.

FIGURE 08-72: A thinner, lighter flywheel, called a flexplate , is used to connect the torque converter of an automatic transmission to the engine.

FIGURE 08-73: This flywheel has a dowel pin to verify that the flywheel is installed in the correct position.