Valves

In a combustion engine, an intake or exhaust valve usually consists of a disk with a stem, which is opened by a cam and closed by a spring.

The lifter typically translates the rotational motion of the cam to a reciprocating linear motion in the linkage system.

Also, it signifies the total intake and exhaust valves in an internal combustion engine. For example, a 24-valve V-6 would have 4 valves per cylinder 24/6=4. A 16-valve V-8 would have 2 valves per cylinder 16/8=2. More valves allow the engine to breathe better at high RPM and produce more power.

Closing Force

The force needed for the spring to close a valve.

Timing

The angle made by the crank with its top or bottom dead-center position at which some valve opens or closes.

Valve Float

A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components. The onset of valve float prevents higher-rpm operation. Extended periods of valve float will damage the valvetrain.

Valve Lifter

The cylindrically shaped component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates. Most valve lifters have an oil-lubricated hardened face that slides on the cam lobe. So-called "roller lifters", however, have a small roller in contact with the cam lobe: thereby reducing the friction between the cam lobe and the lifter. Also known as a valve follower.

Valve Seat

That part of the valve mechanism upon which the valve face rests to close the port.

Valve Spring

The spring which is used to close a valve.

Valve-Spring Retainer

The part which is held against a groove or grooves on the valve stem and in turn holds the valve spring in a state of compression.

See also: Cam Follower, Camshaft, Internal Combustion Engine, Timing.

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Subjects: Engines