This was posted on Volvo 1800 list, I think it's worth a reading if you do
not know what harmonic balancers are for (just like I did not know..)
Tadek
Re: Harmonic Balancer
Posted by: "zemog1ja" zemog1ja@yahoo.com zemog1ja
Sun Dec 6, 2009 7:07 am (PST)
Jim, I've been reading the responses to the the harmonic balancer post
and even though I feel that it's up to each individual owner to do
whatever to their engines, perhaps a better explanation about the
mechanics of a vibration damper will help all of us to decide whether
to install one or not. When the crankshaft throw receives the force
of the piston on the power stroke, the crankshaft twists slightly. This
twisting may be so minute that is not measurable. It may only strain
the crankshaft, causing stress in the metal without exterior movement.
But the heavy crankshaft resists the strain, and after the initial push
from the piston and connecting rod, pushes back. In effect, the piston
tries to bend the crankshaft, and the crankshaft tries to straighten
itself. When the crankshaft pushes back, it over-reacts and then tries
to straighten itself in the other direction. These oscillations take
place for several cycles and finally die out, similar to a tuning fork.
Everytime there is a firing impulse in the engine, the crankshaft gets a
push and starts vibrating again. At certain speeds, the pushes received
by the crankshaft occur simultaneously with the efforts of the
crankshaft to straighten itself. This increases the magnitude of the
osciallations. At certain speeds the vibration can become so great that
the shaft will break. This vibration is called torsional vibration. It
can cause heavy wear on timing chains. The sprocket at the fron of the
crankshaft constantly osciallates against the chain. Torsional
vibration rarely causes any problems at the flywheel end of the engine
because the heavy flywheel dampens the oscillations. The harmonic
balancer, located at the front pulley on the crankshaft, is made of an
outer heavy ring, a rubber ring, and an inner hub. When the crankshaft
oscillates, the balancer oscillates with it. When it gets to the end of
the oscillation, the outer ring keeps going and twists the rubber
slightly. The outer ring stretches the rubber and dampens the torsional
vibration in the crankshaft. Since each engine will give out different
oscillations then the damper must be tuned to the crankshaft. Whether
the harmonic balancers are made of rubber rings or frictional material
and springs these willl wear out and must be replaced. Sorry about
the long winded explanation but it was the only way to fully explain the
function and purpose of the harmonic balancer.
Bill63S
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