PeachParts Mercedes-Benz Forum - View Single Post

Tomguy · #15 10-08-2019, 04:49 PM

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.