Does a Harmonic Balancer ever fail

[Tony H]

45+ years old and has rubber elements-do they fail? Can't imagine they last forever. I see rebuilding services on the net. Are they "tuned" for specific parameters?

[Tony H]

Did some research-they fail slowly over time as the elastomer hardens and loses it's elasticy or they can fail catastrophically as well. So it's not doing anything anymore. They can be rebuilt with more modern silicone elastomer injection.

[Tomguy]

I know it's not an MB, but here's one that was 18 years, 208k miles or so at the time.

[Tony H]

Wow-bad. I never knew what they did until I did some research. It's more of a shock absorber than a balancer; absorbing the individual combustion impulses on the crankshaft.

[Benz Dr.]

I've rebuilt a lot of MB engines and I've never seen one come apart. Like anything mechanical, they can break or wear out, but I think it's not all that common.

[rocky raccoon]

A new(er) car I know but ...

My wife's 2008 E320 (Diesel) lost hers and it took the serp belt which also took the power steering pump. A $1900 repair by the dealer.

[Usaguy]

There a basically 2 designs of harmonic balancers:


1. Rubber insulated part drives the belt - those tend to fail and can leave you stranded


2. belt pulley is connected directly to the crank and the rubber insulated part doesn't drive the belt - those rarely fail and even if they do you don't loose your belt and lucky for us almost all old mb (+30 yrs) have this style.

[ACCD]

They absolutely fail, wear out. Just replaced one on my 93 300ce. When it starts to make noise, nasty, deep rattling sound, get it repaired ASAP.

[oldsinner111]

may I ask something on this. I always thought a balance,and blueprinted engine,never needed a balancer
,just a crank pulley

[Benz Dr.]

Originally Posted by oldsinner111

may I ask something on this. I always thought a balance,and blueprinted engine,never needed a balancer
,just a crank pulley

How do you suppose it was balanced in the first place?

[oldsinner111]

Balance they weigh pistons,rods,pins, to match,crank is shaved here and there,so no runout. Block bored perfect

[Tony H]

From what I understand the harmonic balancer is not really a balancer but an absorber of harmonics created by the combustion pulses. It is not passive-it has an active element.

[oldsinner111]

so blueprinted motors have them too? I thought they were a fast way to balance mass produced motors

[Frank Reiner]

Originally Posted by Tony H

From what I understand the harmonic balancer is not really a balancer but an absorber of harmonics created by the combustion pulses. It is not passive-it has an active element.

This statement is the correct understanding of the function of the harmonic dampner/absorber. The device is NOT involved in the balance of the rotating/reciprocating assembly. It is not a "balancer" at all.

Every crankshaft will have a natural torsional resonant frequency. Think of the crankshaft as a torsion bar, suspend it rigidly by one end, and give the free end a torsional displacement (twist). When the twist force is released the crankshaft will oscillate about its axis at some frequency. That is its natural frequency. When in the engine and running, at some RPM the power pulses will be of a frequency that matches the natural frequency of the crankshaft. At that frequency the natural torsional resonance will be amplified by the power pulses and can become great enough to cause damage to bearings and camshaft drive components, and in the extreme case lead to outright breakage of the crankshaft.
The harmonic dampner absorbs and reduces the intensity of the torsional resonance.

[Tomguy]

Yep, two main purposes of it.
1) Reduce torsional loads on the crank itself caused by drive accessories,
2) Reduce vibration and noise in belt-driven accessories.

Like Frank said, the crank is not a solid rigid piece of metal - it has harmonics. Also, when it's being slammed by multiple pistons at multiple angles, they can induce OPPOSING harmonics. Ex: in an inline engine, when a cylinder fires, the nose of the crank will bend up in an opposite reaction. in a V engine, it bends at the angle away from the firing cylinder. These miniscule vibrations can cause extra stress if, say, the engine RPM harmonics from firing collide with the crank's innate harmonics or external ones, such as if a tight belt is hard-mounted to the crankshaft, causing crank snout failure for example. Some engines are actually known for this specific failure mode, like early Miatas.

The harmonic balancer serves to prevent not only crank failures by displacing what could be a runaway harmonic causing the crank to fracture, but also helps prevent accessories, such as the water pump, from suffering similar fates.

Just because an old MB crank pulley (harmonic balancer) may not hard-fail doesn't mean it's still doing its job as needed. Old, hard rubber can mean you're essentially driving your engine harmonics in a bad way and causing crank (or accessory) stress.