In a message dated 97-04-16, Kirk Cowen wrote:
<< The pulley function is only part of the job it does. It also functions
as a crankshaft vibration (impulse) damper. You must remember that
BMC/Leyland NEVER spent any money on their products that they weren't
forced to; and that a one piece casting would be cheaper than the two
piece vibration damper that they used, so there must have been a good
reason for them to use it. >>
Indeed there was! As the crankshaft rotates, each crank throw alternates
between being DRIVEN BY the piston on the power stroke, and DRIVING the
piston on the compression stroke. The forces on the throws from these events
are in opposing directions, creating vibration on the crank. The elastic
material in the pully/dampner absorb most of the shock, making the engine run
smoother, and prolonging engine life. There is more to it than that, but this
simplified explaination gives a good reason for NOT using a solid pulley.
(Engine vibration is a very complicated subject, involving 2nd and 3rd order
harmonics, counterweights, etc.)
Dan Masters,
Alcoa, TN
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