<VV> Harmonic balancer

[Craig Nicol]

Chris wrote:
I know where it goes but am clueless about what it does. Why is it called a
harmonic balancer?
And do they fail or where out?
Chris mann

Craig replies:
A crankshaft is something of a noodle; it twists under load.  Every time a
piston has a power output stroke, the crankshaft twists or "winds up" and
then when the powerstroke is over, it unwinds. All of this force occurs
between the connecting rod in question and the flywheel.  By installing a
mass (the harmonic damper/balancer) at the opposite end of the crankshaft,
the twisting force is split: Some of the force is applied to the portion of
the crank between the connecting rod and the flywheel and some is applied
between the connecting rod and the harmonic balancer. Splitting the torque
lowers the stress on the crankshaft and reduces the possibility of cracking.
In addition to splitting the force, the balancer also reduces the peak force
by absorbing the peak and slowly releasing the energy - this is the function
of the rubber coupling between the center hub and the heavy outer ring.  The
balancer is tuned to absorb force or dampen forces at a specific frequency
("harmonic" frequency) where the crankshaft can destructively resonate
(ring) that is known to be damaging to the crank.

Over time, the rubber ring deteriorates and the outer ring begins to slip -
when this occurs the balancer can no longer absorb the peak forces and
eventually the ring will come off the hub resulting in damage to the oil
filter and other items near the uncontrolled heavy flying ring. Alignment
marks on the hub and ring indicate a slipping ring. Timing marks will also
be inaccurate if the ring has slipped. 

A 6-cyl crankshaft accelerates and slows three times for each revolution.
Late model cars use this phenomenon to determine engine misfire - no
acceleration = misfire.  The harmonic balancer reduces these impact loads to
prolong crankshaft life and avoid catastrophic crankshaft fractures.