All about the camshaft on Harley-Davidson motorcycles

We often hear about this internal engine component, which is one of the most unknown in terms of its characteristics. The camshaft isn't a component that's commonly replaced when upgrading custom motorcycle engines, probably due to a lack of awareness of the actual changes in engine performance after replacement.
We'll explain the basics of how it works so you can fully understand how to decide if you're interested in replacing your original camshaft with a high-performance one.

The function of the camshaft
This element is responsible for opening and closing the valves at the right time to produce the four strokes of the engine: intake, compression, combustion, and exhaust.

Although in theory the valves remain in the positions shown in the image, in reality, and because air has mass and inertia, the valves open a little earlier and close a little later than their respective times. This is why, for the same motorcycle, there may be different camshafts, with different characteristics, which will change the way the engine "breathes."
The camshaft consists of 1 shaft on Big Twin Evolution models, 2 shafts on TwinCam models

and 4 axles on Sportster models.

These shafts rotate in conjunction with the crankshaft at half speed and have an oval-shaped part that pushes the rod, which in turn opens and closes the valve.

But which one is better?
When I have to explain which is the best camshaft for a particular engine, I compare it to the gearbox, which everyone understands: it is not "better" for the engine to run in one gear or another; the ideal gear will depend on the conditions of use and driving.
The same thing happens with camshafts; we must choose the right one taking into account several factors:
-The main use of the motorcycle (sport, city, loaded travel...)
-Our driving style (relaxed, aggressive, jumping the gun at traffic lights, or towing a trailer)
-The type of engine and the modifications we have made to it (if we have an engine with a lot of torque simply because it is very large, we can sacrifice a little torque without hardly noticing it; if the engine goes up to a lot of RPM, we can choose a suitable shaft to work in this range...)
One of the main characteristics that the camshaft will determine is the point of maximum torque: in the same engine, if maximum torque is produced at low RPM, we will have strength, acceleration, and ease of handling; if it is produced at high RPM, we will have power, speed, and we will have to drive with more "joy."
In short, the camshaft does not increase or decrease power or torque, it simply changes the point where these variables reach their maximum value, changing the “personality” of our engine.

Types of camshafts
When choosing our camshaft, it's highly recommended to consult a recognized professional, who will advise us on our selection based on our engine's components and our expectations for its performance.
It should be noted that the original camshafts are not fully optimized to take advantage of the maximum engine performance because they must comply with strict emissions and noise regulations. Therefore, replacing this component, even one with very similar values to the original, will provide changes in engine performance, slightly increasing maximum torque and power.
A key point when choosing our ideal camshaft is to look at the degrees of closure of the intake valve after the BDC (Bottom Dead Center). This information is provided by the component manufacturer:

-Less than 30º will provide us with a high-torque engine at low RPM, ideal for acceleration and heavy motorcycles.
-30º to 50º is generally a camshaft that boosts mid-range revs, perfect for light motorcycles and fast riding.
-More than 50º are used in racing and tuned engines, which are constantly driven at high RPM and where power is paramount.

Let's get to work
Once you've chosen your camshaft, all you have to do is purchase the appropriate gasket kit and replace it, following the manufacturer's instructions (with very aggressive camshafts, it's often necessary to modify some components such as the valve springs or pushrods) and the workshop manual for your model.
We're going to perform the swap on a 103ci Softail engine, installing a Crane camshaft that will give the engine a broader torque curve, giving us more power from very low revs up to almost 5000 RPM, with hardly any loss of power.

Comparing the camshafts in the previous photo, we see the differences in the valve opening lobes. Crane's higher manufacturing quality is also evident, with an improved finish.
We will lift the rocker arms to remove pressure on the camshafts,

We will carry out the replacement (you can consult this other technical article for more details on how to change the camshaft in a Twin Cam engine) and we will reassemble it, following the manuals to the letter and respecting procedures and tightening torques.

Adjustment and calibration
Once the installation is complete, we need to modify the fuel injection map to adapt to the engine's new "breathing," as we will have increased its volumetric efficiency at many points in the map. We will do this by programming the ECU.

After which we can test the bike on the road to observe the change in the "character" of the engine.