Engine Distribution Systems: OHV, OHC, and DOHC Mechanics

Engine Distribution Systems

OHV (Overhead Valve): In this system, the valves are located in the cylinder head and the camshafts are in the block. The opening occurs as the cam rotates, moving up the tappet and the pushrod, which makes the rocker arm pivot, acting on the valve.

OHC and DOHC: The OHC is a single camshaft for both intake and exhaust. DOHC features one camshaft for intake and another for exhaust.

Control of the Distribution

For every two crankshaft turns, the camshaft drives one. This can be done by:

• Gear wheels: These are used only when it is an OHV system.
• Chain: Formed by two roller sprockets responsible for dragging a chain that can be single or double. It also includes a tensioner charged to maintain tension and offset the effects of wear. This is a very sturdy rubber heel that is applied against the chain with constant pressure by a spring; this system requires constant lubrication.
• Timing belt: This is the most used system, and its advantages are that it requires no lubrication, is quiet, and is very economical.

Valves and Their Components

Valves are elements that open channels for intake and exhaust. At least one intake and one exhaust valve are mounted per cylinder, and they are cooled by the passage of fresh gas from the intake.

Manufacturing: They are made from one piece of raw material that is molded by heating and given shape by pressure, therefore retaining their original properties. Intake valves use chrome-silicon, and intake materials retain their properties at high temperatures.

Valve guides: This is the piece that slides on the rod in its movement and focuses the valve on its seat. It is manufactured in cast iron with a special alloy.

Valve Seats: The element that is supported on the head of the valve to close it.

Valve spring: The spring provides the force necessary to keep the valve closed and is mounted with a prior tension that is transmitted to the valve through the retention plate and the semiconductor.

Camshaft Function and Constitution

The camshaft is the element that governs the distribution system and sets the angle of opening and closing of the valves. It receives the rotation of the crankshaft and transmits it to the valve against the force of the spring.

Constitution

It consists of many cams and valves in the engine, arranged so that they make the movement of the valves according to the distribution chart. It can be mounted on practically every block, although it is often mounted in the cylinder head.

Intermediate and Tilting Elements

Intermediate Tappets: They are powered directly by the cam, and their mission is to increase the contact surface between the pieces so that wear is reduced and lateral stresses are better distributed. In OHV systems, they act on the pushrod, and in OHC systems, they act directly on the valve.

Pushrods: These rods are used when the camshaft is mounted in the block, and their mission is to transmit motion from the tappets to the rockers.

Rockers (Tilting Elements)

Rockers are levers mounted on an axis at their center. They receive the thrust of the cam at one end, which is transmitted to the valve at the other. These levers are driven by pushrods in OHV systems or directly by the cam in OHC systems.