ENGINE BLOCK COMPONENTS

There are many components and subcomponents of the engine block. This lesson will discuss the seven major components and their related parts. These major components are the camshaft pistons, connecting rods, crankshaft, flywheel, vibration damper, and oil pan. Let's begin with the camshaft.

1. The Camshaft

Camshafts are usually made from cast or forged steel. The surfaces of the lobes are hardened for long life. In most cases the camshaft is located in the engine block and is supported, and rotates, in a series of bearings located along its length. Its purpose is to provide for the opening and closing of the engine valves.

2. The Pistons

When a flammable gas mixture is ignited and burns, the gases expand producing heat and pressure. If the heat energy has nothing to work on, it will do nothing more than warm an area. The function of the piston is to convert the heat energy into mechanical energy. The piston is a hollow metal tube with the top enclosed. It is on this enclosed top that the heat energy works. The energy produced by the heat drives the piston down inside the cylinder in the same manner that gunpowder would drive a cannonball through the barrel of a cannon when fired. If the energy produced by the burning gases is allowed to pass between the piston and the cylinder walls, it is wasted energy; therefore, you must have a pressure-tight seal between the piston and the cylinder walls. Take a look at the piston below As you can see, near the top of the piston is a series of lands and grooves. 

THE PISTON

To obtain a pressure-tight seal, a series of rings is installed into the grooves near the top of the piston. Just below the lands and grooves is a hole that extends through the piston. There are two types of rings--compression rings and oil control rings. The top two rings are the compression rings and are responsible for forming the pressure-tight seal.

The piston moving in the cylinder causes friction. Even though the smooth surface of the cylinder walls helps to reduce the friction, the smooth surface is not enough. To further reduce the friction, the cylinder walls must be lubricated with oil but we cannot allow excess oil to remain on the cylinder walls. Oil remaining on the cylinder walls would be burned with the gases when the piston travels down inside the cylinder. Eventually there would be no more oil. To prevent or at least minimize this situation, the bottom ring, the oil control ring (usually a three-piece ring) wipes excess oil from the cylinder wall as the piston travels downward. 

PISTON RINGS

3. Connecting Rod

So far, you have heat energy being converted to mechanical energy by the pistons; but like heat energy, mechanical energy must have something to work on. If not, it is wasted. The piston traveling straight down must cause the wheels of the vehicle to rotate. That is, the up and down motion (reciprocating motion) of the piston must be converted to rotary motion. The crankshaft, which delivers power from the engine, goes around in a rotary motion, but the pistons must be connected to the crankshaft in a way that will allow for this change of motion to occur. A component known as the connecting rod does this.

This is where the hole in the side piston is employed. A snug-fitted pin called the piston pin is manufactured for this hole. The pin attaches the connecting rod to the piston. This is done by inserting the pin through the holes in the side of the piston and through the piston pin bushing (a friction-type bearing) located in a hole at the top of the connecting rod. The connecting rod is allowed to swing freely on the piston pin in much the same manner as your hand swings on your wrist. (For this reason, you will often hear the piston pin referred to as the wrist pin.) The bottom of the connecting rod is connected to the crankshaft by a bearing cap. 

CONNECTING ROD AND RELATED PARTS

4. Crankshaft

As stated previously, the crankshaft delivers power from the engine. The function of the crankshaft when aided by the connecting rod is to change the reciprocating motion of the pistons to rotary motion.

The crankshaft extends through the length of the engine and has a series of throws and journals. Some of these journals are on the shaft itself, and others are located on the throws. The journals on the centerline of the shaft are main journals; those located on the throws are connecting rod journals. Notice that the throws cause the connecting rod journals to be offset from the centerline of the crankshaft.

The main journals connect the crankshaft to the crankcase while still allowing the shaft to rotate. A main bearing cap is bolted over each of the crankshaft's main journals after the crankshaft is positioned in the crankcase. 

CRANKSHAFT CONSTRUCTION

The connecting rod journals provide a place to attach the connecting rod to the crankshaft. After the connecting rod is seated on the crankshaft, a connecting rod bearing cap is bolted over the journal to the connecting rod. Therefore, when the piston is driven down in the cylinder, it drives the connecting rod, which drives the crankshaft throw (or counterweight) causing the crankshaft to rotate.

 

RECIPROCATING MOTION TO ROTARY MOTION OF THE CRANKSHAFT

5. Flywheel

In some engines, there is a brief interval when the pistons do not drive the crankshaft. However, with enough momentum, the crankshaft can travel through this brief portion of its rotation. To accomplish this, a large wheel known as the flywheel is bolted to the rear end of the crankshaft.

6. Vibration Damper

Under certain engine speeds and loads, the crankshaft tends to vibrate. To reduce this vibration, a small wheel known as the vibration damper is bolted to the front end of the crankshaft. Vibration dampers often serve as a pulley for the fan, generator, and accessory belts or they may have a pulley attached to accommodate the various belts. Below image shows what the components would look like if they were assembled outside the engine block. 

VIBRATION DAMPER LOCATION

With the exception of the flywheel and the vibration damper, all the moving parts discussed up to this point require lubrication (engine oil) stored inside the engine oil pan. So let's discuss the oil pan. 

7. Oil Pan

The oil pan is a reservoir for engine oil. It is a large metal pan fitted and bolted to the bottom of the crankcase. It encloses the crankcase and all moving parts. Oil is picked up from the oil pan by the oil pump and distributed throughout the engine. 

OIL PAN AND RELATED PARTS