66 Diesel Technology Copyright Goodheart-Willcox Co., Inc. rods, there is an oil hole in the big end of the rod opposite the rod cap. This hole is the entrance to an oil gallery that runs up the center of the rod to lubricate the piston pin and to spray oil to cool the piston’s underside. Incorrect installa- tion of the rod bearing will cover this hole, blocking the flow of oil, and causing engine failure. Oil Pan The oil pan forms the bottom of the engine. It is bolted to the bottom of the cylinder block with bolts and sealed with a soft gasket. The area formed by the oil pan and the bottom half of the cylinder block is called the crankcase, since it encloses the crankshaft. One of the oil pan’s major jobs is to provide a reser- voir for the engine’s lubricating oil. The lowest part of the oil pan is called the sump. The oil pickup tube extends into the sump and is covered by a coarse wire screen that pre- vents dirt and bits of metal from entering the lubrication system and damaging the engine. There are many different oil pan designs, such as front, center, and rear sump con- figurations, Figure 4-11. By changing the shape of the oil pan, the same engine can be made to run upright, on its side, or even upside down. Flywheel The pistons do not supply a smooth continuous flow of power to the crankshaft. Instead, they provide individual power pulses that result in a rough, jerky turning motion. To compensate for this motion, a flywheel is used to store some of the kinetic (or motion) energy of the power strokes. Flywheels are large, flat disks and are usually made of heavy cast iron or steel. The flywheel uses its momentum to push the pistons during the exhaust and compression strokes. Top dead center is the position in the stroke when the piston is at the very top of the cylinder. Heavy flywheels can store more energy than light flywheels. The rear surface of the flywheel may be ground smooth and used as one of the contact surfaces for the clutch disks. The ring gear for the starter motor is an integral part of the flywheel assembly, Figure 4-12. The flywheel housing is mounted to the cylinder block. It supports the starter motor and protects the clutch or torque converter. Some diesel engines are rigidly coupled to heavy loads that serve the same purpose as a flywheel. These installations include generator set armatures, torque con- verters, and large fans and propellers. Vibration Dampers The vibration damper is mounted on the front of the crankshaft next to the accessory pulleys. Its job is to help absorb the torsional harmonics (lengthwise twisting) in the crankshaft. This twisting is a result of the multiple power strokes or pulses received from the connecting rods. When subjected to these forces, the crankshaft can begin vibrating like a giant tuning fork along its entire length. The longer the crankshaft, the more difficult it is to control torsional vibration. The vibration damper may use a ring of viscous fluid or heavy rubber and steel rings to absorb and dissipate crankshaft vibrations. Some larger diesel engines have a complex system of weights and springs in their vibration dampers. Smaller dampers usually consist of a heavy cast iron rim with a rubber ring located between the rim and the damper’s hub. Internal Balancers An internal engine balancer is actually an extra shaft that is geared to the crankshaft. It turns in the opposite direction of crankshaft rotation at a speed that is the same Front Sump Sump Drain plug Rear Sump Figure 4-11. Two common oil pan configurations found on mobile engines. Other designs are used on both mobile and stationary diesel engines. Flywheel Ring gear for starting motor Figure 4-12. The starter ring gear is part of the flywheel assembly. This gear can be replaced separately from the flywheel in most cases.