Chapter 6 Engine Types and Classifi cations 137 Copyright by Goodheart-Willcox Co., Inc. Engine crankshaft Drive gears Timing belt Balancer shaft A B Camshaft Camshaft sprocket Balancer or silent shafts Balancer or silent shaft drive belt Figure 6-25. Balancer shafts can be used to make the engine run smoother at idle. Counterweights on the shafts help keep the crankshaft spinning on non-power-producing strokes. A— Simple balancer shaft. B—Turbo diesel balancer shafts. (Ford) No power to solenoid Blocker plate in place Body Rocker arm held in place Rocker arm slides up Pedestal Push rod Valve closed Valve open Cam acts on lifter Blocker plate retracted Fulcrum Pedestal Solenoid energized Cylinder Active Cylinder Inactive Figure 6-26. Cylinder deactivation engines simply dis- able rocker arms to keep certain cylinders from working and consuming fuel. This design is old and these engines are rare. (General Motors) A few engines are externally balanced. Extra weight is added to certain points on the flywheel and balancer to prevent engine vibration. A balancer shaft is sometimes used to help smooth the operation of the engine, Figure 6-25. A balancer shaft, also called a silent shaft, is an extra shaft with counterweights. The weights on the balancer shaft are positioned to coun- teract the non-power-producing strokes. A chain, belt, or set of gears connected to the crankshaft is used to spin the balancer shaft, usually at twice the engine speed. Two bal- ancing shafts are frequently used in one engine. A four-cylinder engine normally runs very rough at idle. Vibration can be felt at idle in the passenger com- partment. The balancer shafts help keep the crankshaft spinning between power strokes. With the balancing shafts, low speed smoothness is increased tremendously. Only a small amount of energy is needed to spin the shafts so there is little reduction of fuel economy. Alternative Engine Designs Cars and light trucks generally have a four-stroke cycle, piston engine that operates on one of two fuels—gasoline or diesel fuel. However, there are several alternative engine designs in production or development. Some of these designs are variations of the four-stroke cycle, piston engine. Other designs have a completely different operational design. This section describes several alternative engine designs. Cylinder Deactivation Engine A cylinder deactivation engine (CDE), sometimes termed a variable displacement engine (VDE), uses solenoid-operated rocker arms to alter the number of engine cylinders that function during engine operation. By dis- abling rocker arms, valves, and fuel injectors, the number of cylinders firing and using fuel can be reduced. This, in effect, reduces the displacement of the engine. When accelerating, all of the cylinders and rocker arms function normally. However, when cruising speed is reached and there is a less demand for power, the computer can deac- tivate cylinders to improve fuel economy. Figure 6-26 shows the basic parts of a cylinder deacti- vation engine. This is not a very common design. Even with the valves deactivated, the rings, bearings, and other mov- ing parts in the “dead” cylinders still contribute to frictional losses and reduce efficiency. Variable Compression Ratio Engine A variable compression ratio engine (VCRE) can alter the volume of its combustion chambers, and thus its compression ratio, for improved operating efficiency. In this design, the cylinder sleeves are attached to the cylinder head, but are free to move up and down in the cylinder block. The engine is also supercharged. As shown in Figure 6-27, the cylinder head is movable or tiltable. One side of the cylinder head is mounted on a pivot bar. The other side of the head is positioned by an