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On 4 Jun 2004 at 20:18, Jeff wrote: > I know I should know this term, as it's > tossed around a lot, but what does it > really mean, and what is it's function? The crankshaft moves in many different ways in addition to just the round and round motion that we all think of. One of these ways is for it to vibrate in a torsional manner, as in the two ends vibrating back and forth, rotating in opposite directions. Because of the large flywheel mass on the drive end, that end doesn't move much, which leaves the pulley end with a lot of rather high frequency torsional vibration. This vibration, because of it's high frequency, can eventually cause fatigue failure of the crank. Adding an additional "flywheel" at the pulley end of the crank reduces the vibrational resonant frequency thus extending the time it takes to accumulate enough cycles for fatigue failure. Adding a bit of energy dissipating rubber in there will actually damp the vibrations, reducing the potential for damage even more. Our fans do both, since they have mass at a large radius as well as a hub that is linked to the fan with a rubber collar. You can't see this rubber part unless you drill out the rivets, but it's there. -- ******************************* Jim Adney, jadney@vwtype3.org Madison, Wisconsin, USA ******************************* ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org