Engine construction

While multi cylinder engines contain parts, which perform the same function as those in a single cylinder engine,

They are more complex and have many more parts. However, it is easier to understand how an engine is constructed if it is first broken down into section before considering the complete engine. For our purpose, looking at internal parts at the top of the engine, the front of the engine, and the rear of the engine, the main internal parts, and finally the components of an engine assembly will do this.

Components at the top of the engine


These are the parts that are included in what is sometimes referred to as a top overhaul of an engine parts that can be identified in the illustration are:

  1. Timing belt.
  2. Camshaft timing pulley
  3. Camshaft
  4. Rocker arms and shafts
  5. Valves and valve springs
  6. Piston

The timing belt drives the camshaft pulley, which is attached to the camshaft. The cams on the camshaft operate rocker arms, which pivot on their shafts to open and close the valves. The intake valves are opened to admit air-fuel mixture, and the exhaust valves are opened to discharge the burnt gases

Components at the front of the engine.


The parts located at the front of the engine, including those in the previous illustration.

These are:

  1. Piston
  2. Connecting rod
  3. Crankshaft timing pulley
  4. Timing belt
  5. Crankshaft pulley and balancer

The piston is shown on top dead-center (TDC). On the power stroke, combustion pressure forces the piston down on the power stroke. Through the connecting rod, this rotates the crankshaft so that the engine operates.

The crankshaft-timing pulley (or sprocket) drives the timing belt, and this rotates the camshaft to operate the valves as described before. The crankshaft pulley (drive pulley) is a different one to the timing pulley `and is used  to drive parts on outside of the engine – the fan, water pump alternator, power steering and the air-conditioning compressor (these parts are not shown). The pulley is part of vibration damper that helps to reduce engine vibration.

Components at the rear of the engine

A section of the rear of the engine is shown in figure below.

The parts shown are:

  1. Starter ring gear
  2. Flywheel
  3. Piston
  4. Connecting rod
  5. Crankshaft flange

The starter has a pinion, which engages with the ring gear on the flywheel. When the starter is operated, it spins the crankshaft, the pistons are moved up and down, and fuel is taken into cylinder. The fuel is ignited by the spark plugs so that the engine starts and runs. The flywheel is bolted to a flange on the rear end of the crankshaft. It is a heavy cast iron wheel that is used to make the engine run smoothly. It does this by absorbing energy during a power stroke and releasing energy during the other strokes.

Components at the bottom of the engine

Figure below illustrates the lower part of the engine.

The parts shown are:

  • Four pistons
  • Connecting rod
  • Crankshaft
  • Crankshaft balance weights
  • Crankshaft main bearing journals

The crankshafts have number of cranks to which the connecting rods are attached. A bearing between the connecting rod and the crankpin reduces friction and wear. The upper end of the connecting rod is connected to the piston with a large a large piston pin. This allows the connecting rod to move in relation to the piston, with a wrist-like action.

The crankshaft is supported in the crankcase by five main bearings. Only the journals are shown. The journals are the parts of the shafts that run in the bearings. They are accurately ground to produce a fine surface finish. The crankshafts have a number of balance weights. These masses are located opposite the crankpins to balance the crankshafts.

The crankshafts and its bearings are sometimes referred to as the bottom end because they are near the bottom of the engine. The bottom end of the connecting rod is sometimes referred to as he big end because it is the larger end of the connecting rod.

Internal components of the engine.

Figure this below combines all the previous parts of the engine and shows all the main operating parts. These are the valve mechanism, timing belt, crankshafts, piston, connecting rods, and the flywheel.

There are four valves per cylinder. Two intakes and two exhausts. The camshafts pulley is twice the size of the crankshafts timing pulley, so that the camshafts rotates t half the engine speed. A timing belt connects the timing pulleys. This has teeth, which mesh, with the teeth on the pulleys. The camshafts has a cam for each valve and is designed with its cam in the correct position to open the right valve at the right the time. Also, the camshafts is ‘timed’ to the crankshaft

Dismantling at the front of the engine

Parts located at the front of the engine include the water pump (on most engine), the crankcase, pulley and vibration damper, the timing cover and the timing chain or timing belt. Engines with a timing chain have a cast-metal or pressed-metal cover which has to retain oil. Engines with a timing belt have a plastic timing cover. This keeps out dirt, but does not have to be oil-tight because the timing belt runs dry.

Removing crankcase pulley

The pulley fits on the end of the crankcase on a key and is retained by a bolt or nut. A puller could be needed to remove the pulley. After removing the bolt or nut, the puller is fitted to the pulley as shown this below.

Removing the timing cover

Metal timing covers are retained by a number of bolts and can be removed after the crankcase pulley has been removed. There will be a gasket or sealing material between the timing cover and the cylinder block. The timing cover is removed and treated in a similar way to the oil pan.

A lip-type seal is used between the crankcase and the timing cover. It must be renewed if it leaks. The seal is punched out and a new seal installed with a suitable tool as shown in this below. Before the seal is installed, grease should be packed behind the seal to provide initial lubrication

Removing the timing belt

A number of small automotive diesel engines are using a timing belt to drive the overhead camshaft, the fuel injection pump and other engine accessories. The belt is made of a composite rubber material with a toothed pattern on its inside running surface.

During engine operation, the belt wears, and at specified service internals it must be replaced. The majority of timing belt require changing T 100000 Km. However, if the belt shows signs of abnormal wear or deterioration, as shown in figure 11.33,then it should be replaced earlier than the recommended change interval. Failure to change the timing belt at the correct service interval may result in the belt breaking, which will allow the piston to strike the valve, Causing major internal engine damage.

A general procedure for removing a timing belt is as follows:

  • Remove all the covers from around the timing belt area.
  • Rotate the engine crankshaft and align the timing marks for the crankshaft, the camshaft and the injection pump.
  • Release the belt tensioned mounting bolts and pull the tensioned away from the belt.
  • Remove the belt.

Harmonic balancer (vibration damper)

Harmonic vibration is high frequency vibration resulting from twisting and untwisting of the crankshaft. Each piston and connecting rod assembly can exert over a tone of downward force on its journal. This can actually flex (bend) the crank throws in relation to each other. A harmonic balancer, also called a vibration damper, is a heavy wheel mounted in rubber to control harmonic vibration.

Begin by removing any bolts on pulleys attached to the vibration damper, or harmonic balancer, next remove the retaining cap screw in the end of the crankshaft, if used. If a retaining screw was used, the damper may now slide off the crankshaft. If the damper must be pulled off, attach a suitable puller to the damper hub (do not pull on the outer rim) and with draw the damper.



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