Valve timing

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In a piston engine, the valve timing is the precise timing of the opening and closing of the valves.

In four-stroke cycle engines and some two-stroke cycle engines, the valve timing is controlled by the camshaft. It can be varied by modifying the camshaft, or it can be varied during engine operation by the relatively new technology of variable valve timing. It is also affected by the adjustment of the valve mechanism, and particularly by the tappet clearance; This variation is normally unwanted.

Many two-stroke cycle and all wankel engines do not have a camshaft or valves, and the port timing can only be varied by machining the ports. Some supercharged two-stroke diesel engines do however have a cylinder head and camshaft similar to a four-stroke cycle engine.

In a steam engine, the control of the valve timing is an important part of the operation of the engine. See valve gear, and also Walschaerts valve gear, Berry accelerator valve gear, Baker valve gear, Woolf valve gear, Caprotti valve gear, Corliss valve gear.

[edit] See also

• Four-stroke cycle#Valve Timing.
• Cylinder head porting.

[edit] External links

• Berry accelerator valve gear.

• Steam locomotive valve gear simulation software, listing twenty types of locomotive valve gear.

• The impact of valve timing on engine performance and emissions.