Harmonic Balancers - The Most Important Crankshaft Component Explained

The heart of every vehicle is the engine block and it's been evolving ever since it was first made. Cylinders and pistons are what make the combustion process possible with the help of air and fuel. But there is one component that is crucial for transferring the power generated by the cylinders and pistons. The crankshaft sits right below them and converts their movement into rotation which is sent to the flywheel and transmission. This is how a vehicle works on a fundamental level and it all depends on one small component called a harmonic damper/ balancer.

This metal device may not provide power to the engine or affect its performance directly it is still quite an important one. The pulley-like device is mounted onto the crankshaft, on the side opposite from the flywheel and it's made of two cast iron components. These components are fit together with the help of a rubber ring. A harmonic balancer is there to absorb the vibrations from the valve train and rotating assembly. These harmonic vibrations would otherwise destroy the engine's main bearings. You can say that a balancer is what keeps everything running smoothly by working quietly in the background. Often an underrated component it can also vary when it comes to the parts it's made of.

There are three different types of balancers, elastomer, friction-style and viscous (fluid). An elastomer harmonic balancer is the one mentioned above with the rubber connecting the two metal pieces. These usually come stock on the vehicle and offer solid performance. Whilst stock elastomer balances are nothing out of the ordinary there are aftermarket ones that are fine-tuned to meet specific RPM ranges. This means that you can find elastomer balancers that can handle high-performance applications.

Friction-style dampers/ balancers use a set of clutch discs that help control the vibrations. With varying styles and sizes of the discs alongside the spring-loaded pressure, the effectiveness of these balancers is at a high level. This is because manufacturers are able to tune the dampers to a specific RPM range make it them highly versatile.

Viscous harmonic dampers are filled with thick fluid which is often silicone placed between the outer housing and inertia ring. The vibration causes the inertia ring and housing to spin back and forth a shearing action occurs within the fluid. This action converts the vibrations into heat which dissipates through the outer housing. Viscous harmonic dampers are usually more expensive than their rubber-reliant counterparts.

This is because viscous balancers are able to handle a broader RPM range, maybe not as broad as friction-style balancers but definitely broader than elastomer ones. For viscous balancers, it's said that they can be more effective at higher RPM ranges. This is due to the fact that the fluid inside of them is not bonded to the damper itself, giving it an unlimited ability of movement.

The diameter of a balancer can also affect its performance. But finding the right type of diameter depends on multiple things such as torque, engine stroke, rpm range, cubic centimetres and so on. For example, the greater the torque and the longer the stroke of the engine the larger the diameter of the balancer. But keep in mind that bigger balancers affect acceleration and revving. With the right diameter and mass, you'll have the perfect balance.

In case your balancer is going to be used in competitions then it'll need to be one that's SFI 18.1 – approved. This approval is assigned to dampers that can be driven at rotational speeds between 12,500 and 13,500 RPM for at least an hour. Otherwise, any type of balancer will do.

The timing marks which are located on the front of the pulley between the rubber layers can shift. This can cause their placement to be thrown off which makes it extremely difficult to time the engine with a timing light.

A more serious symptom if an issue with the balancer is when the part itself becomes separated. If the rubber layer holding the two metal pieces together dries or wears off it can make the balancer fail completely. This then causes it to separate and when it does the engine belts are typically the ones to come off. This results in the vehicle being left out of any engine accessories.

Although vibrations are something that the harmonic balancer is required to prevent sometimes they can occur which is a cause of concern. Vibrations in the engine occur when the balancer fails or gets to the end of its lifespan which means that it cannot absorb the vibrations properly. This will cause the engine to shake excessively especially when at high speeds. This shaking will be more pronounced and more dangerous the more you drive the vehicle and if you often do so at a high speed.