After reviewing engine balancing in our previous feature, we'll now be talking about distribution and timing for 4-stroke internal combustion engines, with a focus on camshafts.

Regardless if it's a single- or dual-cylinder engine, the timing system will either use a single or double overhead cam design. The decision to rely on one or the other depends on a variety of factors and needs, such as torque delivery, performance and even engine sound. As you can probably imagine, designing camshafts is no easy task.

The role of this all-important component is to open intake valves at a specific time to let a precise amount of air-fuel mixture into the combustion chamber and to open exhaust valves to allow dissipation of exhaust gases produced during the combustion process. The camshaft needs to be perfectly calibrated and operate with extreme precision to ensure proper engine performance.


Let's take a closer look. First of all, when the piston reaches the peak of its stroke (also known as top dead center), the intake valve creates a vacuum inside the intake manifold. The valve remains open until the piston drops back to the lowest point of its stroke (also known as bottom dead center). With Honda's CBR600, for instance, the total opening extends over 255 degrees.

As for the exhaust cam, the opening starts once the combustion is complete, slightly before the piston reaches the bottom dead center. During the actual combustion process, both valves are completely closed to ensure perfect airtightness of the chamber. Therefore, the exhaust valve opens slightly before the bottom dead center and closes slightly after the top dead center.

When the exhaust valve closes, the intake valve has already started opening. That's what engineers call "valve overlap", a crucial step for the efficiency of the air-fuel delivery. Engine output is partly determined by this phase.

The shape and height of the cam also impact performance. A well-designed camshaft will be slightly protruding so as to generate more acceleration in the first place and then a slight negative acceleration (in the opposite direction). This will improve the air-fuel delivery and, consequently, engine performance. A more ovoid cam design will result in greater power at high RPMs.