Compression release

The 2012 Ducati 1199, equipped with an electric starter, uses a compression release that is automatically activated at low engine speed by a centrifugal flyweight on each exhaust cam.

This reduces the work needed to spin the high 12.5:1 compression ratio engine, allowing for a smaller battery and starter motor, amounting to a total weight saving of 3.3 kilograms (7.3 lb).

[2] From the mid-1960s to the late-1970s, engine compression releases were also used to supplement rear wheel braking on many two-stroke motorcycles, primarily those used off-road or for various types of dirt-track racing, such as motocross and flat-tracking.

Small diesel engines may be fitted with compression release valves if they are to be started by hand cranking.

Once the engine spins to starting speed, centrifugal force causes the lever to move out of the way, and the exhaust valve is allowed to seat fully.