Engine Operation 10 UENR4490-01 Cylinder Head Pistons, Rings, and Connecting rods Illustration 6 g02466936 Typical example (1) Valve keepers (2) Valve spring retainer (3) Valve spring The engine has a cast iron cylinder head (5). The inlet manifold is integral within the cylinder head. There are two inlet valves and two exhaust valves for each cylinder. Each pair of valves (6) are connected by a valve bridge that is controlled by a pushrod valve system. The ports for the inlet valves are on the left side of the cylinder head. The ports for the exhaust valves are on the right side of the cylinder head. The valve stems move in valve guides that are pressed into the cylinder head.
There is a renewable stem seal (4) that fits over the top of the valve guide. The valve seats are replaceable. Illustration 7 g03728612 Typical example The pistons (9) have a Quiescent or a Re-entrant combustion chamber in the top of the piston in order to provide an efficient mix of fuel and air. The piston pin (8) is off-center in order to reduce the noise level. The position pin (8) is retained in the correct position by two circlips (3). The pistons have two compression rings (1) and an oil control ring (2). The groove for the top ring has a hard metal insert in order to reduce wear of the groove.
The piston skirt has a low friction coating in order to reduce the risk of seizure when the engine is new. The correct piston height is important in order to ensure that the piston does not contact the cylinder head. The correct piston height also ensures the efficient combustion of fuel which is necessary in order to conform to requirements for emissions.