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If your vehicle is free from engine vibration you can thank the harmonic balancer attached to your engine’s crankshaft. A harmonic balancer, or as many refer to them as either a harmonic damper, harmonic dampner, or a harmonic dampener works to keep your engine spinning smoothly. We’re not here to give a grammar lesson, we’re here to talk about everything harmonic balancer, and how it impacts your vehicle’s performance. When it comes to harmonic balancers, there are so many options, but we’re here to help you make a vibration-free decision that is right for your build and your budget.

How Does a Harmonic Balancer Work?

In a nutshell, a harmonic balancer keeps an engine from vibrating itself into a million pieces by converting the engine's vibrations into heat, which is transferred to various parts of the harmonic balancer that is attached to the front of the crankshaft. A harmonic balancer or harmonic damper is designed to improve engine dynamics by absorbing any vibration due to the crankshaft’s rotational forces. Even if the engine’s rotating assembly is internally balanced, the job of a harmonic balancer is still to absorb vibration. With an engine’s pistons, rods and crankshaft slinging in every direction, the harmonic balancer is tasked with absorbing the torsional forces from the rotating assembly. Controlling engine vibration goes a long way in ensuring your engine bearings will last long after the break-in period. Knowing which harmonic balancer to get depends on the engine you plan to have under the hood.

A harmonic balancer Ford 302 application is matched to the engine’s flexplate or flywheel to keep vibration at bay, while other engine combinations are internally balanced and have no need for an external balance harmonic balancer. A harmonic balancer Chevy 350 application can be either internally or externally balanced. To make sure you have the right harmonic balancer SBC application, 305 and 350 engines with a 2-piece rear main seal feature an internal balance, but a harmonic balancer Chevy 350 application for a 1-piece rear main seal can be either internally or externally balanced. A harmonic balancer 454 application will be an external balance, as will a small block 400. A harmonic balancer Ford 302 and 351 Windsor application will be an external balance, but the Ford modular engine is an internal balance, as is the Chevy LS family of engines. Knowing if your engine is internally or externally balanced will play a big role in whatever harmonic balancer you choose.

Mopar engines are the same way in that some are internally balanced, and others are externally balanced. What you need to do is if you have a factory-built engine, figure out if it’s internally balanced or externally balanced, and go from there. However, if working with an engine builder, the way they put together a rotating assembly will decide the avenue you go down as to whether you choose an internally balanced or externally balanced combination. That will help decide which harmonic balancer you will need.

Can A Bad Harmonic Balancer Cause Vibration?

Yes, a harmonic balancer or harmonic damper can go bad and cause a vibration. Most factory harmonic balancer designs are made of two circular pieces of steel bonded together by a rubber or elastomer material. Most factory harmonic damper designs consist of a hub, then an elastomer or rubber material, and an outer ring. All three pieces are bonded together and pressed or bolted to the snout of the crankshaft. In some cases, oil leaks or exposure to various fluids or chemicals can cause the rubber to break down and over time, become separated. When that happens, a vibration is usually the first sign of an issue with your harmonic damper, and you will need to replace the harmonic balancer.

Fluid dampers are a type of SFI harmonic balancer that use a flywheel suspended within a specialized fluid to dissipate harmful vibrations. Due to its greater ability to manage heat (remember: a damper converts vibration energy into heat), a fluid balancer is more effective across a wider operating range. Plus, all moving parts are fully self-contained in the SFI balancer, allowing it to meet SFI 18.1 safety ratings for extreme racing conditions. TCI's Rattler line is constructed in a similar way, except without the fluid. The Rattler is unique in its ability to absorb energy, rather than convert it to heat. An SFI harmonic balancer is needed if running 10.99 or quicker in the quarter mile for drag racing and is often required in other sanctioned racing series as well.

Are Harmonic Balancers Interchangeable?

Within engine families, yes, a harmonic balancer SBC application will fit a wide range of Chevy small block engines. However, you can’t take a harmonic balancer SBC example and fit it to a Ford small block. Speaking of which, Ford small block engines can share the same harmonic balancer, and with different weights available, can be used with either 28- or 50-oz flywheel and flexplate options. Most harmonic balancer options we list, if they’re an externally balanced harmonic damper, will come with the required weight to mate them to the properly weighted flywheel or flexplate. The harmonic balancer SBC options include different sizes, as well. The big difference between harmonic balancer applications is how the crank pulley attaches, and how many bolts it uses. This is one of the main reasons you can’t take a harmonic balancer off one engine and just blindly put it on a totally different engine from a different engine family or manufacturer.

How Long Do Harmonic Balancers Last?

Generally speaking, a harmonic balancer isn’t one of those engine components that stands out as something that needs replacing. They can last the lifetime of a vehicle in many cases, even way over 100,000 miles. When you see the rubber separating from the hub or outer ring, or flopping around while the engine is running, you need a new harmonic balancer. If you notice increased engine vibration, or excessive engine bearing wear, mismatched timing marks, or various other engine maladies, a bad harmonic balancer could be the issue. When replacing a harmonic balancer, don't forget these install/removal tools to ensure you don't damage the balancer or crankshaft.

Are All Harmonic Balancers the Same?

Harmonic balancer designs are available in either elastomer (rubber), fluid, or friction designs. Most factory harmonic balancer designs are of the elastomer variety. A fluid harmonic balancer uses fluid as its vibration absorbing material, while friction designs use clutches or clutch packs to defeat a crankshaft’s torsional deflection. Some harmonic balancer designs use both fluid and clutch packs to keep vibration at a minimum. Some harmonic damper designs are available in both internally and externally balanced applications. As an example, harmonic balancer 454 applications and small block Ford applications are available with different bolt-on weights that can be used to mate the harmonic balancer to a specific weight balance flywheel or flexplate, but also be left off for use with an internally balanced engine.