The Independent American Magazine for all Mini Owners
Issue link: http://mc2.epubxp.com/i/33538
A cut-away of the rebuildable ATI Super Damper. Unlike conventional bonded XQLWV WKH LQHUWLDO PDVV LV captured between two SDUWV RI WKH KRXVLQJ DQG uses non-bonded o-rings. T he harmonic damper, or crank pulley, is an important but not well-understood part on modern engines. It turns out that more than their fair share have failed on the first generation MCS, so it’s also a part that many of you will be getting to know, whether you want to or not! I’m hoping to help those that do end up needing to work on this part (or who are thinking about making a change for aesthetic or other reasons) so that they can make a well-informed decision. But before we dig into the depths of this important part, we have to spend some time on how power is created. When the spark plug ignites the air/fuel mixture a controlled burn ensues. This presses on the top of the piston that in turn twists the crank. There are two key concepts here: Pressure in the combustion chamber rises very quickly (about a millisecond). The impact on the piston isn’t quite as traumatic as a hammer blow, but it is also far from gentle. The second concept is that of crank twist. This is really where the problems start. It’s hard to imagine the crank twisting or doing anything other than just turning the push of the piston into the rotation that feeds the transmission. But really, it’s a very stiff spring! While this doesn’t make much sense at first, all materials deform a bit when pushed. The materials used in the crankshaft are chosen such that they don’t deform much, and if they do bend a bit, they bend so little as to “spring back” to their un-deformed shape, ringing a bit as well, just like a tuning fork. In an engine, these events repeat time after time, many times a second. At some RPM, these twists are additive, and make the total twist and oscillation grow larger and larger. This is called constructive interference or resonance, and is very bad for an engine if left unchecked. As the twists get larger and larger, a couple of bad things start to happen: The most obvious is that the phasing of the different parts of the crank changes. Because the end near the flywheel has the least twist, and most engines drive the camshafts from the other end of the crank, valve timing can be affected and HP can drop! But another problem is more insidious than just loss of HP. This resonance vibrates everything connected to the front of the crank very severely. In extreme cases, this vibration can lead to total engine failure! All engines go through several different RPM where resonance occurs, so engine builders design it so that the amplitude of these oscillations is controlled. This is where the harmonic damper comes into play…. So what does the harmonic damper do? It’s a little shock absorber for your crankshaft! Just like the shock absorber for your wheel, it dissipates energy so that the oscillations stay small and controlled. Now, longer cranks have more problems than shorter cranks. Inline six-cylinder and V-12 engines probably have by Matt Richter photos by the author and ATI Performance Products Issue 30 MC2 Magazine 35 The Crank Pulley W h a t i t i s, ho w i t w o r k s, a n d ho w t o rep l a c e i t .