The valve train typically includes the camshaft, valve lifter, rocker arm, rocker arm shaft, valve, valve spring and valve guide. On engines with traditional mounting of the camshaft in the cylinder block, the valve train also includes lifters and pushrods. Overhead cam engines may use more than one camshaft per cylinder head. Engines use different valve configurations, such as two, three, four or five valves per cylinder. These various valve arrangements are used for different engine breathing requirements. Some engines also use variable valve timing, which allows the engine to change breathing characteristics under different operating conditions. Valvetrain opening/closing & duration controls the amount of air and fuel entering the combustion chamber at any given point in time. Timing for open/close/duration is controlled by the camshaft which is synchronized to the crankshaft by a chain or belt.
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In an internal combustion engine, the cylinder head sits atop the cylinders and consists of a platform containing part of the combustion chamber and the location of the valves and spark plugs. In a flathead engine, the mechanical parts of the valve train are all contained within the block, and the head is essentially a flat plate of metal bolted to the top of the cylinder bank with a head gasket in between; this simplicity leads to ease of manufacture and repair, and accounts for the flathead engine's early success in production automobiles and continued success in small engines.This design, however, requires the incoming air to flow through a convoluted path, which limits the ability of the engine to perform at higher rpm, leading to the adoption of the overhead valve head design.
Connecting Rod Movement:
The connecting rods are most usually made of steel for production engines, but can be made of aluminium (for lightness and the ability to absorb high impact at the expense of durability) or titanium (for a combination of strength and lightness at the expense of affordability) for high performance engines, or of cast iron for applications such as motor scooters. They are not rigidly fixed at either end, so that the angle between the con rod and the piston can change as the rod moves up and down and rotates around the crankshaft.
The connecting rods are most usually made of steel for production engines, but can be made of aluminium (for lightness and the ability to absorb high impact at the expense of durability) or titanium (for a combination of strength and lightness at the expense of affordability) for high performance engines, or of cast iron for applications such as motor scooters. They are not rigidly fixed at either end, so that the angle between the con rod and the piston can change as the rod moves up and down and rotates around the crankshaft.
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