When rebuilding or tuning an engine for more power, the changes to the stock layout result in additional forces that can prove counter-productive. Higher rev lines, added torque and more horsepower from reworked internals or stroker kits to increase displacement must be balanced so all parts work seamlessly. This is where harmonic balancers enter the engine tuning scene.

Basics of Engine Harmonics and Balancers

Engine harmonics is the sum of different vibrations generated when the engine spins to create power. This can include unbalanced vibrations, resulting from changes to pistons and conrods, forward and backward axial vibrations in the crank, and torsional vibrations resulting from the twisting and rebounding of the crankshaft in each engine cycle. Precisely matching pistons, conrods and crank counterweights deal with most unbalanced vibrations while thrust bearings and main bearing support plates handle axial vibration, Most problems though stem from torsional vibrations. The constant twisting and rebounding of the crank accelerates wear in all connected components, robs the engine of power and can potentially seize the entire assembly. This happens when engine RPMs match the natural resonance of the turning assembly. Though rare, the result is a snapped crank and a huge repair bill.

Many cars (especially bigger V8s) have a crankshaft harmonic balancer slapped onto the front crank pulley. This is a circular device, usually consisting of a metal outer and rubber interior. The rubber absorbs and minimises vibrations, thus preventing engine wear and maintaining smooth power transfer. OEM balancers are designed with the stock internals in mind, so when swapping out pistons, conrods or going with a reworked crank, consider whether the factory balancer can handle changes to torque and engine speeds.

Why Upgrade? 

Harmonic balancers are masters of multitasking. They minimise torsional vibrations with each crank rotation and prevent the likelihood of severe engine damage. This also reduces lost power, especially as RPMs increase. Moreover, they dampen the effect of excessive vibrations on moving parts, so smaller but still vital bottom-end engine parts such as main bearings and conrod bolts endure less wear. The same goes for top-end components like valve springs, and parts directly linked to the crank pulley, including timing and serpentine belts. 

Going with stroker kits, changing engine geometries, using forged internals, or pushing more air into the cylinder with turbo and supercharging are all major upgrades that significantly increase power output, and as a result, extend power bands and engine vibration. The stock balancer won’t be able to function under the increased stress, with the rubber soon wearing out due to higher temperatures, and cracks forming in the rubber interior. Other signs besides engine wobble or pronounced noises are oil pump failure, snapped timing belts, and off-timing, particularly misfires. Depending on the vehicle, you can also get a check engine light in the dash. Choosing a performance harmonic balancer is only a logical addition to any engine upgrades. 

Balancer Types

Elastomer

These are found in stock applications and consist of a rubber material mated to the crank hub and the inertia ring or weight. This is the part that dampens and nulls much of the vibration. Performance variants can include multiple rubber rings and increased thickness and hardness in tune with engine output. Design specifics, such as varying ring diameters, can also work at engine speeds where vibrations are most noticeable. 

Viscous or Fluid Balancers 

This type of crankshaft harmonic balancer gets its name from a viscous fluid, usually silicone, placed between an internal inertia ring and metal outer housing. As teh inertia ring and housing start to spin and differ in frequency, a shearing action is created inside the fluid and this converts the vibrations into heat. excess heat is dissipated out of the outer housing. The design is more effective than elastomer harmonic balancers and can control vibrations across a wider RPM range. You’ll see these are stock equipment in high-end production cars. They can also be added as aftermarket upgrades on tuned vehicles. 

Friction Balancers

A less common design uses a set of clutch discs. These can be of varying sizes and matched with inertia rings and springs to exert different amounts of pressure at varying engine speeds. The working principle is similar to fluid balancers. When the crank rotates, the clutch pack slips, and converts vibrations into heat. Friction balancers are another upgrade to consider if teh stock rubber balancer isn’t up to the task, and you need more power from the engine without tearing it to bits. 

Choosing the Right Harmonic Balancer 

The parts are sold for both factory and modified cars, with the main buying factor being size. The overall diameter of the balancer must suit engine displacement, output numbers, and factors like turbocharging creating abrupt increases in torque. Generally, the bigger the engine, the bigger the balancer. This though increases weight (and affects acceleration) so consider balancers made of lightweight metal housings to dial in the correct mass for your engine. Lastly, only buy balancers that have been safety tested (to double the operational engine speeds) to ensure they last when you’re harder on the acceleration pedal.