The eight major mechanical components of the basic engine are the following parts:
- Cylinder block
- Cylinder head
- Connecting rods
- Timing gear case and gears
- Rocker shaft assembly
Typical Cylinder Block
The cast iron cylinder block for the engine has four cylinders which are arranged in-line. The cylinder block is made of cast iron in order to provide support for the full length of the cylinder bores. Worn cylinders may be rebored in order to accommodate oversize pistons and rings.
The cylinder block has five main bearings which support the crankshaft. Thrust washers are installed on both sides of number 3 main bearing in order to control the end play of the crankshaft.
Passages supply the lubrication for the crankshaft bearings. These passages are cast into the cylinder block.
The cylinders are honed to a specially controlled finish in order to ensure long life and low oil consumption.
The cylinder block has a bush that is installed for the front camshaft journal. The other camshaft journals run directly in the cylinder block.
The engine has a cooling jet that is installed in the cylinder block for each cylinder. The piston cooling jet sprays lubricating oil onto the inner surface of the piston in order to cool the piston.
A multi-layered steel (MLS) cylinder head gasket is used between the engine block and the cylinder head in order to seal combustion gases, water, and oil.
Typical cylinder head
The engine has a cast iron cylinder head. The inlet manifold is integral within the cylinder head. There are two inlet valves and two exhaust valve for each cylinder. Each pair of valves 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 machined into the cylinder head. There is a renewable valve stem seal that fits over the top of the valve guide.
The pistons have a Quiescent combustion chamber in the top of the piston in order to provide an efficient mix of fuel and air. The piston pin is off-center in order to reduce the noise level.
The pistons have two compression rings and an oil control ring. The groove for the top ring has a hard metal insert in order to reduce wear of the groove. The piston skirt has a coating of graphite 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.
The connecting rods are machined from forged molybdenum steel. The connecting rods have bearing caps that are fracture split. The bearing caps on fracture split connecting rods are retained with Torx screws. Connecting rods with bearing caps that are fracture split have the following characteristics:
- The splitting produces an accurately matched surface on each side of the fracture for improved strength.
The crankshaft is a spheroidal graphite iron casting. The crankshaft has five main journals. Thrust washers are installed on both sides of number 3 main bearing in order to control the end play of the crankshaft.
The crankshaft changes the linear energy of the pistons and connecting rods into rotary torque in order to power external equipment.
A gear at the front of the crankshaft drives the timing gears. The crankshaft gear turns the idler gear which then turns the following gears:
- Camshaft gear
- Fuel injection pump and fuel transfer pump
- Lower idler gear which turns the gear of the lubricating oil pump.
Lip type seals are used on both the front of the crankshaft and the rear of the crankshaft.
A timing ring is installed to the crankshaft. The timing ring is used by the ECM in order to measure the engine speed and the engine position.
The crankshaft oil seal is mounted in the aluminum timing case. The timing case cover is made from pressed steel.
The timing gears are made of steel.
The crankshaft gear drives an upper idler gear and a lower idler gear. The upper idler gear drives the camshaft and the fuel injection pump. The lower idler gear drives the oil pump. The water pump drive gear is driven by the fuel injection pump gear.
The camshaft and the fuel injection pump rotate at half the engine speed.
The engine has a single camshaft. The camshaft is made of cast iron. The camshaft lobes are chill hardened.
The camshaft is driven at the front end. As the camshaft turns, the camshaft lobes move the valve system components. The valve system components move the cylinder valves.
The camshaft gear must be timed to the crankshaft gear. The relationship between the lobes and the camshaft gear causes the valves in each cylinder to open at the correct time. The relationship between the lobes and the camshaft gear also causes the valves in each cylinder to close at the correct time.
The camshaft has two camshaft lobes for each cylinder. The lobes operate either a pair of inlet valves or a pair of exhaust valves. As the camshaft turns, lobes on the camshaft cause the lifter to move the pushrod up and down. Upward movement of the pushrod against rocker arm results in a downward movement that acts on the valve bridge. This action opens a pair of valves which compresses the valve springs. When the camshaft has rotated to the peak of the lobe, the valves are fully open. When the camshaft rotates further, the two valve springs under compression start to expand. The valve stems are under tension of the springs. The stems are pushed upward in order to maintain contact with the valve bridge. The continued rotation of the camshaft causes the rocker arm, the pushrods, and the lifters to move downward until the lifter reaches the bottom of the lobe. The valves are now closed. The cycle is repeated for all the valves on each cylinder.