Engine Distribution Systems and Valve Train Components

Role and Components of Distribution

The distribution system has the mission to allow the entry of the mixture and the gas outlet. The arrival and exit must occur at times that are adequate and synchronized.

Distribution System Components

This compounds the valves and the other synchronized components of the crankshaft with intake valves and exhaust valves, along with their systems and support-tree fixing cams, rocker-actuating mechanisms, and mechanical or hydraulic pushers.

Distribution Set and Performance

Valve synchronization with the crank, its opening times, and speed travel are crucial for engine performance and emissions. There are various ways to mount the distribution, from the very simplest to complex and effective systems, though costs may be high. We can distinguish the following systems and configurations:

• Shutter system according to the lights: 2-stroke rotary valve, 2-stroke reciprocating valve, and 4-stroke.
• Location of valves: "Valves in the block system" (SV). All elements of the distribution are hosted on the block; however, this system is no longer used.
• Head-valve systems: These favor the circulation of gases. There are two configurations depending on the position of the camshaft: in the block (OHV) and in the cylinder head (OHC).

Cylinder Head Configurations

Within the cylinder head, there are two options: SOHC (Single OverHead Camshaft) or DOHC (Double OverHead Camshaft).

OHV Provisions

Valves are located in the head, while the camshaft is in the block. The transmission of motion from the cams to the valves is done by way of levers actuated by pusher rods. This system is used very little due to the quantity of elements and the brunt of its limitation regarding high revolutions and weight.

OHC Drive Systems

In OHC systems, valves are in the head or cylinder head, and the camshaft is also located in the cylinder head. This simplifies the mechanism, requiring very few components. Often, rockers, tappets, or semi-rockers are used.

Camshaft Drive Mechanisms

Several systems exist for driving the camshaft: timing belts with tensioners or gear trains. These systems can be mounted on any motor. Another possible system is operated by a remote tree, though it is used very little.

Belt and Gear Types

The transmission of movement is achieved by a toothed flexible belt. The teeth of the belt can be of different types to adapt to the requirements of the engine; the most used types are trapezoidal and round. This system offers total simplicity due to the mechanical materials used. Operation is quiet, and disassembly and assembly do not offer complications due to its situation.