Understanding the Camshaft: How It Works and Which One to Choose

When you ask a biker, they'll tell you that motorcycles have a soul, a personality of their own.
If the heart of our engine is the oil pump, the lungs are the cylinders, and the brain is the ignition switch, then following this analogy, the camshaft would be the character or personality.
This element is decisive and determines the behavior of our engine, since its design defines the delivery of torque (and power). To give an example, if a 100 hp engine is fitted with a different camshaft, this won't increase power, but it will change HOW and WHERE this power is delivered. If this power delivery is progressive and maximum torque is obtained at low or medium revs, we will have a motorcycle that is easy to ride in any gear, powerful, and ideal for accelerating, traveling, and navigating around the city. If, on the other hand, the engine torque is delivered in a more concentrated manner and at high revs, we will have a motorcycle with a sportier and more aggressive character, ideal for releasing adrenaline and braking quickly.

The cams
The camshaft's function is to open and close the intake and exhaust valves in the cylinder head, thereby controlling the filling and emptying of the cylinders.

It is a rotating element that has eccentric lobes (cams) that push the rods that move the valve train (as in Big Twin models), or the valves directly (as in V-Rod models).

By varying the shape of the cams, you can control the length of time the valves remain open (duration) and how far they open (lift). Therefore, when choosing this component, it is essential to consider the characteristics of the engine in which it will be installed and the vehicle's primary use.
There are engines with a single camshaft, such as the Evolution or the Milwaukee Eight,

with two trees, like the Twin Cam (hence the name of this engine),

with three trees like the Indian Thunderstroke,

or with four independent camshafts as in the Sportster models...

Emissions compatibility
Like almost all engine components, the original camshaft is designed to ensure proper engine operation within current regulations, not optimal performance. Therefore, replacing this component with a high-performance one will optimize air intake and exhaust, instantly improving overall performance.

Technical characteristics
When selecting a camshaft from different manufacturers, we must take into account its characteristics, which can be summarized as follows:

• Lift or Opening: Determines the height of the lobe and how far the valve will rise from its seat.
• Duration: Marked by the width of the lobe, it indicates how long the valve remains open.
• Timing: Indicates when the valves open and close in relation to the piston position.

A key factor that will tell us the "character" of a camshaft is the intake valve closure relative to bottom dead center (BDC). Generally, if it's less than 30°, it's a low-RPM camshaft; if it's 30° to 50°, it's a mid-range camshaft or one for light motorcycles. If it's more than 50°, we're talking about optimization for high RPM or highly powered engines.

How to choose a camshaft
When replacing our camshaft there are 2 basic issues that are worth knowing:

• What is the main use of the motorcycle and riding style?

• What are the engine features, and what other modifications have been made to the motorcycle?

Final conclusions
As you may have noticed, choosing the camshaft is a complex and very important decision, as it will greatly influence the performance and sensations the engine transmits.
It is therefore essential to think of this component as another part of the whole, complementing, optimizing, and enhancing its main features.

Frank Burguera

#harleymechanics