Jim,

Yes there is some confusion between a harmonic balancer and damper, but the
device I'm referring to uses an elastomer tuned to a specific frequency to
clip harmonic resonance.

This has nothing to do with balance, which can be addressed in the ways you
mentioned -- counterweights, balance shafts, etc. An engine can make a lot
of vibration and shaking (up and down and side to side) and not have a
problem with torsional resonance.

The opposite is true too -- a very smooth engine can all of a sudden break
its torque shaft from torsional resonance. That's why torsional resonance is
known as the silent killer.

Regards,

Gordon.



"Jim Carriere" wrote in message
.. .
Gordon Arnaut wrote:
For example, most V-8 engines come with a harmonic balancer, even though
they have four power pulses for each crankshaft rotation. That's because
there is enough flex in the crankshaft that the crank can begin to
resonate at some rpm within the operational range.

Actually, V-8s have a harmonic balancer because they would otherwise have
a first order imbalance. The physics explanation is pretty long and
doesn't make a lot of sense anyway, but it's because the crankpins are 90
degrees apart (inline fours don't have this imbalance because the pins are
in pairs 180 degrees apart, but they have second order imbalance
instead... that is what a pair of balance shafts cures) and the mass on
the ends of those crankpins (rods and pistons) flinging around are at
different distances along the crankshaft. Also, the harmonic balancer on
a V-8 is two weights, one on each end of the crankshaft. A lot of people
don't realize there are two weights, not just the one on the front of the
engine.

Harmonic dampers are a different animal. They will smooth out power
pulses on any engine configuration. Harmonic balancers have nothing to do
with power pulses and everything to do with complicated vibration of large
pieces of metal moving back and forth in different directions and
different places.

I think the terms balancer and damper are confused with each other because
they look almost the same- a big part attached to the front of the
crankshaft to make the engine smoother.