<VV> Unique fan belt keeper-oner (Now, Those Flapping Belts)

[RoboMan91324 at aol.com]

Mel,

The fan belt will still want to flap and I would think that there would be 
noise concerns with the belt hitting the sleeves.  Also, I think the belt 
would probably wear out fairly quickly.  At that point, it would probably be a 
PITA to replace the belt especially if it happened on the road.  If the 
belt fails catastrophically, you might have some guide sleeves being thrown 
around the engine compartment, possibly taking out some other items like a 
distributor cap, fuel line, etc.

If you feel a real need to tinker (the vast majority don't) I think an 
idler wheel as shown in a picture link in a previous post is a much better idea. 
 If it is in constant rolling contact, it will very effectively shift the 
natural frequency of the belt much higher and also diminish the amplitude.  
If it is not in constant contact, it will at least disturb the excitation 
each time the belt flaps far enough to touch it.  If the bearing is free 
spinning and the idler wheel has low enough inertia, the wear on the belt should 
be minimal.

Just an opinion.

Doc
1960 Corvette; 1961 Rampside; 1962 Rampside; 1964 Spyder coupe; 1965 
Greenbrier; 1966 Corsa turbo coupe; 1967 Nova SS; 1968 Camaro ragtop
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In a message dated 1/28/2010 6:33:30 PM Pacific Standard Time, 
mfrancis at wi.rr.com writes:

> This discussion of the belt frequency harmonics gave me the alternate 
> idea of assembling a fixed, two-piece sheet metal sleeve, which would form a 
> close-fitting guide tube around the belt, from the idler to the fan pulley. 
> Has this approach ever been tried?
> 
> The Wright brothers were able to get past these same harmonic problems in 
> the very long chain-drives to their two propellers using metal guide tubes 
> and they never had any failures that involved thrown chains.
> 
> Mel
> 
> ----- Original Message ----- 
> From: <RoboMan91324 at aol.com>
> To: <virtualvairs at corvair.org>; <dkdewald at pasty.net>
> Sent: Thursday, January 28, 2010 6:14 PM
> Subject: <VV> Unique fan belt keeper-oner (Now, Those Flapping Belts)
> 
> 
> > Dale,
> >
> > You are not exactly correct.  Analogies such as you describe are used to
> > understand similarities in different disciplines.  However, the analogy 
> > you
> > draw between the mechanical components and an electrical circuit though
> > correct in general is not the cause of the flapping belt.  I believe we 
> > were
> > talking about the flapping and not so much the variable looseness and 
> > tightness
> > of the belt.  Under the steady conditions of idle, the tightness and
> > looseness variance caused by the crank is minimal but does excite a 
> > particular
> > frequency.
> >
> > The belt flapping is caused by sympathetic vibration that is excited by 
> > the
> > crank pulses Craig described.  The pulse frequency (or a multiple of the
> > pulses) matches the frequency of the section of belt that is vibrating. 
> > To
> > draw a musical analogy, piano tuners often start the process by striking 
> a
> > tuning fork of known frequency and holding it close to a piano string.  
> If 
> > the
> > string vibrates, its natural frequency is the same as the tuning fork.  
> (A
> > multiple of the natural frequency is not likely to happen in this
> > application.)
> >
> > If the vibration of the belt at idle is disturbing, you can change it by
> > one or more of several methods.
> >
> > 1.  You can change the idle speed so that the belt and crank pulses no
> > longer match.
> >
> > 2.  You can change the tightness of the belt.  To use another musical
> > analogy, think about the strings on a guitar.  As you tighten or loosen 
> > the
> > string, its natural frequency changes.  You can easily hear the 
> > difference.
> >
> > 3.  You can change the mass of the belt.  A thicker belt will have more
> > mass per unit length and will want to vibrate at a lower frequency. 
> > Again,
> > think of guitar strings.  The thicker strings (more mass) vibrate at a 
> > lower
> > frequency and the thinner strings (lower mass) vibrate at a higher 
> pitch.
> >
> > Keep in mind that the sections of the belt are different lengths and can
> > change tightness depending on whether you are accelerating or 
> decelerating 
> > as
> > well as other variables.  As an example, you might vibrate a section of 
> > belt
> > under normal idle but it might not vibrate once you load the
> > alternator/generator with headlights, radio, wipers, defrost fan and 
> such 
> > turned on.  This
> > alone could change the tightness of the belt enough to cause a visible
> > change in vibration.  Also, if you make a change as suggested above, one 
> 
> > section
> > might stop vibrating and another start vibrating.
> >
> > Best regards,
> >
> > Doc
> > 1960 Corvette; 1961 Rampside; 1962 Rampside; 1964 Spyder coupe; 1965
> > Greenbrier; 1966 Corsa turbo coupe; 1967 Nova SS; 1968 Camaro ragtop