The cylinder block is the largest part of the engine. It has cylinders in which the pistons operate and bearings that carry the crankshaft. The cylinders and pistons are in the upper part of the cylinder block and the crankshaft is in the lower part. The lower part is called the crankcase. It has webs which carry the crankshaft main bearings.

The crankshaft is fitted to the engine block. It is supported by the main bearings to take the radial loads from the connecting rods. One set of main bearings also has a thrust bearing fitted to it to take loads along the crankshaft.

The large end of the connecting rod connects to the crankshaft and the small end connects to the piston. The piston pin or gudgeon pin connects the piston to the connecting rod.

The piston is fitted with three piston rings. The top two rings seal the piston to the cylinder wall and prevent combustion gases from entering the crankcase. The bottom ring prevents excessive oil from entering the combustion chamber from the crankcase.

The cylinder head is bolted to the top of the cylinder block. A gasket, the cylinder-head gasket, is fitted between the parts to provide a seal. The cylinder head carries the camshaft, the valves and the valve-operating mechanism. Intake and exhaust ports in the cylinder head are opened and closed by the action of valves.

The valve cover fits on top of the cylinder head and covers the valve mechanism. The valve cover is of aluminium alloy. A gasket is fitted between it and the top of the cylinder head to provide an oil seal.

The oil pan, or sump, is attached to the bottom of the crankcase and closes off the internal parts. It also acts as a reservoir for the engine oil. The oil is circulated throughout the engine by the oil pump before returning to the oil pan.

The oil leaving the oil pump passes through the oil filter before it is circulated through the engine. The filter removes particles of carbon or other foreign material from the oil.

The water pump is driven by the fan belt from the crankshaft pulley. It circulates coolant throughout the engine and radiator assembly.

The intake manifold carries the air–fuel mixture into the engine. The exhaust manifold carries the burnt gases out of the engine. Manifolds are flange-mounted to the cylinder head over the inlet & exhaust ports. The inlet manifold is made of alloy and the exhaust manifold is made of cast iron to resist heat.