In light of Simon's explanation, would anyone care to comment on the
advantages of removing the heavy metal cooling fan and replacing it with
an electric fan? Please note that a comparison of electric vs mechanical
fans is not in order: I am concerned with the effect on the valuable
crankshaft pulley.
Thomas James Pokrefke, III
1970 MGB
thomas_pokrefke@juno.com
http://ocean.st.usm.edu/~pokrefke
On Fri, 18 Apr 97 14:49:54 +0200 Simon.MATTHEWS@st.com writes:
> After the posts on the 2-part crank pulleys and alluminium
>pulleys, I
> think it mught be worthwhile to go back to basic principles on
>this.
>
> One has to consider the dynamic nature of the forces in the
>engine.
>
> If order to dampen out movement in the crank, a weight with a
>large
> moment of inertia is required to be fixed solidly to the crank.
>This
> is generally called the flywheel!
>
> Now the flywheel is attached to one end of the crank and there
>will
> undoubtably be twisting in the crank, allowing for much less
>damped
> (more violent) movement at the other end. The question is: why
>have a
> damped pulley? One possible reason might be to eliminate the
>effects
> of the sudden movements (in the crank) on the devices driven by
>the
> pulley, but since the belts must surely stretch, this does not
>seem to
> be a good reason.
>
> The other reason might be to reduce the damping effect of the
>pulley
> on the crank. Using Newton's laws of motion: "for every action
>there
> is an equal and opposite reaction".
>
> The effect of the damper is to 'decouple' the outer part of the
>crank
> pulley during very short pulses from the crank (as it twists).
>The
> inner part of the pulley turns with the crank, but the outer part
>
> turns in a smoother fashion.
>
> The effect of this is to make the crank pulley seem lighter -- at
>
> least when considering the short (fast) pulses in the crank. So
> perhaps an alluminium (lightweight!) crank pulley might work
>after
> all!
>
> I would also suggest that one reason the flywheel is attached to
>the
> back of the engine is that you certainly want to dampen out any
>pulses
> going into the transmission and there anr only 2 ways: 1. Have a
>large
> moment of inertia (flywheel) or 2. have a flexible coupling
> (impractical?). Since the flywheel is required for idling and low
>rev
> operation of the engine anyway, this is what is used.
>
> Regards,
> Simon
>
>
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