An often overlooked part of an engine is the harmonic balancer. Failure in the harmonic balancer can be as simple as a squeaking noise or as catastrophic as an engine failure. Proper service procedures and learning to spot symptoms helps prevent most problems the harmonic balancer may cause.
The purposes of the harmonic balancer
Many people have noticed the heavy metal disk on the front of an engine. What seems very simple is really a precision component. We call the assembly a harmonic balancer but it is not one thing. The harmonic balancer is a precise assembly, with multiple parts.
Engineers often use the harmonic balancer as an attachment for the pulley that drives the accessory belts. The harmonic balancer also serves several other important functions.
As the name implies, the harmonic balancer helps in balancing the engine. Some have offset weights that provide balance to the crankshaft and other internal engine parts. It also has an even more precise function as a vibration damper.
Torsional distortion and the harmonic balancer
Automobile engines are reciprocating assemblies by design. We say this because pistons move up and down in the cylinders. These pistons turn the crankshaft, much as we turn a crank by hand. As each cylinder fires, the piston pushes down on the crankshaft journal causing it to rotate.
This sudden jolt of power applied to the crankshaft also causes a twist. After the initial application of force the crankshaft almost immediately springs back. Engineers refer to the twisting of the crankshaft as torsional distortion. A torsional distortion of up to two-degrees is common. Each cylinder exerts a force as it fires. The effect of the twisting and springing back results in a harmonic, which can destroy the engine.
Harmonics result in greatly increased vibration
Imagine a spring attached to an offset pin on a rotating disk. A slowly rotating disk causes the spring to gently move up and down. At lower speeds, the weight moves in a regular pattern. We may call this a non-critical RPM. If we increase the speed, the weight may start to jump violently. We may call this a more critical RPM. If we imagine several springs, all moving together, this is similar to the forces acting on a crankshaft.
How the harmonic balancer works
At minor-critical RPM, the individual twists cancel each other or at least do not add to the whole. As we reach major-critical RPM the twisting combines, drastically increasing the force. Left unchecked this can cause the crankshaft to break.
Engineers design the harmonic balancer to help dampen this twisting and spring-back. They mount the heavy outer ring of the harmonic balancer to the hub with a pliable rubber. Attaching this to the front of the crankshaft, helps dampen the torsional distortion.
As the crankshaft accelerates, the rubber will twist and allow the mass of the outer ring to slightly lag behind. When the crankshaft snaps back, the mass of the harmonic balancer responds, helping to cancel the harmonic. On the rear of the engine, the flywheel and engine load serve a similar function.
By calculating the precise characteristics of the engine and sizing the harmonic balancer accordingly they control torsional-distortion. This helps to prevent critical harmonics that might break the crankshaft.
Ways a harmonic balancer fails
A harmonic balancer can fail in different ways. A common failure with a harmonic balancer is deterioration of the rubber. Continuous force on the rubber mounting builds heat. Heat builds up and can damage the rubber that bonds the ring to the hub. When this occurs, the balance ring can slip out of position.
Over heating the engine can make the situation far worse. Excessive engine heat will cause damage to the rubber. Another cause of damage to the harmonic balancer is an oil leak. Oil can damage the rubber and drastically accelerate deterioration.
Rubber hardness and the harmonic balancer
A harmonic balancer can also fail without coming apart. The hardness of the rubber in the harmonic balancer is critical. We can measure the hardness of rubber with an instrument called a durometer. Rubber used in the construction of a harmonic balancer may measure around 60 on the durometer scale.
Deterioration makes the rubber softer but age and heat can also cause it to harden. When the rubber gets harder or softer, it changes the frequency of the harmonic balancer. This can result in RPM-related vibration and cause damage to the crankshaft.
We test the hardness of the rubber with a durometer and may need to replace a harmonic balancer when the rubber gets too hard or too soft. This type of diagnosis is not common and often this problem goes mis-diagnosed for a long period. RPM related vibration is often cured by replacing a bad harmonic balancer, though it looks okay.
Catastrophic harmonic balancer failure
An early symptom of a separating outer ring is often noise. A knocking sound from the front of the engine is common. A squeaking noise as the engine rotates may also occur. Often folks may mistake this for a squeaking belt.
Quick diagnosis and repair are important. The outer ring may come off and do tremendous damage to the radiator, water pump and anything in proximity. The failed balancer no longer protects the crankshaft. Continued use may cause the crankshaft to break, immediately destroying the engine.
When the outer ring of the harmonic balancer slips from its normal position, a vibration will result. This vibration may cause the fastener on the harmonic balancer to come loose. When this occurs the hub may slip on the crankshaft and damage the key way they use to index it. Such damage normally requires engine disassembly and very expensive repair. It is also preventable with early diagnosis.
The outer ring should run perfectly true, with the center hub. Any wobble that we can see is likely too much. We can use a dial indicator to measure run-out. Any run-out in excess of 0.010 inches is the cause for alarm. A close physical inspection can reveal many problems. Rubber that is missing, squeezing out of place or dry rotted is a problem and calls for replacement. Never attempt to reassemble a balancer that is coming apart.
Hardened seals can damage the harmonic balancer
On many engines, the harmonic balancer also serves as the sealing surface for the front crankshaft seal. Infrequent oil changes allow the seals to harden. This can cut a groove into the seal surface and ruin the harmonic balancer. Oil leaks out and gets on the rubber holding the harmonic balancer together. Oil leaks may be the cause of or the result of a harmonic balancer failure.
Improper harmonic balancer service
Harmonic balancers are precision devices and improper service may easily damage them. They do not design the outer ring as a place to pull the harmonic balancer from the engine. Using a wheel puller to remove a balancer is a sure way to destroy it. Prying or beating on the balancer will also cause damage.
We remove a harmonic balancer with special tools designed for the job. Many balancers have threaded holes where a puller attaches. Others have special bosses cast into the hub, where we use a special puller to remove them.
They make other tools to install the harmonic balancer onto the crankshaft. We usually thread these into the crankshaft. Tightening a large nut against a bearing gently pushes the harmonic balancer into position. Attempting to remove or install a balancer without the proper tooling will normally cause severe damage.
The large bolt that retains the harmonic balancer is sometimes a torque-to-yield component and we replace it when removed. Always check with service data or replace the bolt to be safe. Torque on the bolt is also critical and we must tighten it to specifications.
Aftermarket harmonic balancers
In recent years, many aftermarket replacement balancers have come into the market. Some of these are okay but they do not build all to OEM standards. Using substandard parts, in such a critical area is not smart. Improper mass, poor machining or low-quality bonding of the rubber can result in a catastrophic failure.
Harmonic balancer repair
When the original part is no longer available, they can sometimes rebuild a harmonic balancer. Specialized services are available to replace the rubber and make other repairs. This is very valuable with an antique vehicle, where original parts are no longer available.
With proper service, the harmonic balancer can last the life of the engine. Inspect and repair any problems quickly. Repairing a minor oil leak can save a major repair. Additionally, use only qualified service professionals, that employ the proper tooling and methods when repairing your vehicle.