C2.2 Engine and C1.5 Generator Set Caterpillar

Naturally aspirated engines pull outside air through an air cleaner directly into the inlet manifold. The air flows from the inlet manifold to the engine cylinders. The fuel is mixed with the air in the engine cylinders. After the fuel combustion occurs in the engine cylinder, the exhaust gases flow directly to the outside air through the exhaust manifold and the exhaust system.

Each piston makes four strokes:

1. Intake

   Air is drawn into the cylinder through the open inlet valve. Fuel is sprayed into the engine by the fuel injection nozzle.

2. Compression

   The mixture of air and fuel is compressed in the cylinder in order to heat the mixture to the temperature of combustion.

3. Power

   The mixture of air and fuel ignites at the top of the compression stroke. The expansion of gases from the combustion forces the piston downward. This force creates the power of the engine.

4. Exhaust

   The piston moves upward in order to force the gases of combustion from the cylinder through the open exhaust valve.

The sequence of the strokes by all of the pistons in all of the engine cylinders provides constant air flow from the air inlet system during the engine operation.

The valve mechanism cover contains a closed breather assembly. The gases in the valve cover, which are caused by blowby, pass from the crankcase to the inlet manifold. The breather is sealed from the outside air by a diaphragm. Above the diaphragm, the cover is vented to the outside air by a small vent hole so that pressure does not build up.

Cylinder Head And Valves

Illustration 1	g00905459
Cross section of the inlet and exhaust valves in the cylinder head (typical example)

Illustration 2	g00905464
Cylinder head and valves (typical example) (1) Collets (2) Valve spring retainer (3) Valve spring (4) Valve seal (5) Valve guide (6) Cylinder head (7) Cylinder head gasket (8) Pushrod (9) Lifter (10) Exhaust valve (11) Inlet valve

The valves and the rocker shaft assembly control the flow of air into the cylinders and out of the cylinders during engine operation. The cylinder head assembly has two valves for each cylinder. Each valve has one valve spring (3). The ports for inlet valve (11) and exhaust valve (10) are on the left side of the cylinder head.

The valve moves along a steel valve guide (5). The valve guides can be replaced.

The inlet valve and the exhaust valve are opened and closed by the rotation and movement of the following components:

• Crankshaft

• Idler gear

• Camshaft

• Valve lifters

• Pushrods

• Rocker arms

• Valve springs

The camshaft gear is driven by the idler gear. The camshaft gear, the idler gear and the crankshaft gear are timed together. When the camshaft turns, the valve lifters are moved up and down. The pushrods move the rocker arms. The rocker arms make the inlet valves and the exhaust valves open and close. This is in sequence with the firing order of the engine. The valve springs force the valves back to the closed position.