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RE: Lighter flywheels

To: "'mark holbrook'" <rolling_rock_12@yahoo.com>, spitfires@autox.team.net
Subject: RE: Lighter flywheels
From: Richard Gosling <richard.gosling@exprogroup.com>
Date: Thu, 18 Oct 2001 08:48:11 +0100
Harmonic balancer?  You've got to be kidding.  OK, I have not got a GT6
engine, nor have I ever inspected one closely, but I'd be very surprised if
any engine from the '60s had a harmonic balancer on it, although I don't
know when they first made an appearance.

It is true that harmonic balancers are designed around a particular
behaviour of the crank, which will change if the flywheel is changed.
Designing the frequency of harmonic balancers was one part of the job I left
a couple of months ago.

The other effect of a lighter flywheel is to remove some of the smoothing
effect  it has on revs, particularly at idle.  Every time a cylinder fires
the crank will speed up a little, every time a cylinder compresses the crank
will slow, and the flywheel reduces these rapid little changes in speed, to
give a smoother idle.  However, the more cylinders you have the less this
effect is anyway, as each firing cycle is closer to the ones before and
after, so for a 6-cylinder engine a lighter flywheel should still not result
in too lumpy an idle.  This is all theory, if anyone has personal experience
it is probably more valid!

Crankshafts should ideally be balanced 'fully dressed', since that is how
they are run.  In fact, in manufacture, masses are frequently bolted onto
the crankpins to represent the conrod and piston masses for the balancing
operation.

Richard & Daffy
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