<VV> Fan belt tension (Clarification)

Sat Apr 14 18:29:19 EDT 2012

     I can put this to rest.  Tension your Corvair fan belt. If it 
appears a little too tight then that is bad - if it seems way too lose 
it will run. I've followed this practice for 44 years and never had a 
belt problem.

     What? The issue isn't put to rest. Damn.

Lon Wall
www.corvairunderground.com


  On 4/14/2012 8:11 AM, jvhroberts at aol.com wrote:
>   Well, temper tantrum aside, rayon, the most common V belt cord material, has a CTE of 120 ppm/C. 356T6 aluminum has a CTE of 19 ppm/C. So, I was off a bit, but clearly the cords in the belt expand a LOT more than the engine case does. The pulleys are steel, and have a CTE of about 9 ppm/C.
>
> So, histrionics aside, the real deal is the belt expands a LOT more with temperature than the engine does. A LOT more. Also, the crankcase gets nowhere near as warm as the heads. And the belt, well, if you're having fun with the car, it gets pretty damn hot.
>
> These are the facts and they are NOT in dispute. So, whatever axe this guy has to grind, grind it privately.
>
>
>
> John Roberts
>
>
>
>
> -----Original Message-----
> From: RoboMan91324<RoboMan91324 at aol.com>
> To: virtualvairs<virtualvairs at corvair.org>; cmckinley313<cmckinley313 at verizon.net>
> Sent: Thu, Apr 12, 2012 9:02 pm
> Subject:<VV>  Fan belt tension  (Clarification)
>
>
> Chuck and All,
>
> I would like to clarify some misstatements made on this  subject.
>
> It has been stated by another that fan belts thermally expand  at a rate of
> about 10 times that of steel, aluminum, etc.  This is  completely wrong for
> several reasons as follow.
>
> 1.  Even if the belts were made completely of polymers,  the polymer would
> expand at 3.3 times that of aluminum.  (0.000041 vs.  0.0000123 Inches per
> Inch per degree F rise).  This is not close to the 10x  claimed.  Of course,
> far worse, it was claimed that the belts (not  polymer alone) had a 10x
> expansion rate which leads to the  following.
>
> 2.  Our fan belts are not merely made of polymer.   They are composites
> made of polymers combined with fibers that are intended to  keep the belts from
> stretching under either tension or thermal expansion.   The relative rates
> of thermal expansion are 0.000017 for a fiber reinforced  polymer vs the
> previously stated .0000123 of aluminum in inches per Inch per  degree F rise in
> temperature.  This calculates to approximately 38% more  expansion for the
> belt as compared to aluminum for the same temperature  rise.  38% is a far
> far cry from the 1000% claimed.  Even this 38%  differential is moot due to
> the following.
>
> 3.  The crankcase of our engines reach a significantly  high temperature
> when driven.  Anyone who has accidentally touched a hot  engine can testify to
> this.  Of course, being air cooled, our Corvair  engines get hotter than
> water pumpers.  While the engine is running, the  belts we use have a very
> benign temperature rise because the only way they  can absorb heat is from very
> short duration contact with the crankshaft  pulley.  The flexing and
> friction also causes temperature rise.   Counteracting this heat gain, the belt
> is
> flapping through fairly cool air in  the chamber above the engine.  As you
> know, this air is constantly pulled  into the upper chamber by the engine's
> fan and has no time to heat up before  being drawn into the engine by the
> fan.  It is very close to the ambient  temperature you and I enjoy outside the
> car.  In addition, a moving section  of the belt is being significantly
> cooled due to the air stream which is pulled  into the fan at the mouth of the
> "Turkey Roaster."  This is what is called  forced convection cooling and it
> is significant.  If the fan belt were to  reach actual engine temperature on
> a regular basis, yes, it would stretch but we  would be replacing them
> every few hundred miles or sooner.  So, while the  belt has an approximate 38%
> greater thermal coefficient of expansion  compared to the aluminum crankcase,
> the belt's temperature will only rise a few  degrees while the engine can
> rise hundreds of degrees.  Remember, the  coefficient of thermal expansions
> is defined with "per degree rise in  temperature."  In the actual  operating
> environment, the engine expands much more than the fan belt in  our Corvairs.
>
> 4.  As stated above, polymers and rubber expand  at 0.000041 Inches per
> Inch per degree F rise.  The fact that the  included fibers prevents the belt
> from growing significantly along its length  does not negate the laws of
> Physics.  The polymer must expand.  If it  cannot grow in length due to the
> fibers, the expansion must relieve itself  somehow.  It does this by "plumping
> up."  In effect, the belt grows  both in depth and width when it heats up.
> The net result is that the belt  will get tighter on the pulleys despite its
> greater coefficient of  expansion.  You might call this a "reverse" thermal
> coefficient and it is  likely that Engineers take this into account when
> designing belts far  application in hot environments.  Of course, this growth
> in cross section  will be minimal because, as stated above, the temperature
> rise of the belt will  be minimal.
>
> For all the above reasons, I think we can accept my contention  that the
> Corvair engine grows more than the belt in real world use.
>
> Next, the belts on water pumpers stay on and last longer  because they are
> in-line unlike the odd configuration of our Corvairs.   They do not twist as
> much as 90 degrees before rushing on to the next pulley as  they do on our
> cars.  This is one reason they can be adjusted  tighter.  This was hinted at
> by another.
>
> Next, on water pumper fans, the clutch decouples the greatest  rotating
> inertia in the cooling system; that being the fan blade  assembly.  To verify
> this, go out to any water pumper with a fan clutch and  turn the fan with
> your finger.  It turns extremely easily.  Because of  this, the effect it has
> on a fan belt when changing engine speeds is nearly non  existent.
>
> Lastly, on water pumpers, if there are multiple driven  components like
> A/C, power steering, etc. they usually have multiple belts  so that each belt
> is not subjected to too much slippage when RPMs change  quickly.  The
> rotating inertia is spread between belts during acceleration  and deceleration.
> Of
> course, this isn't the only reason to use multiple  belts.  Serpentine
> belts usually work alone but they have the advantage of  "dynamic" tightening to
>
> allow slippage as necessary without excessive  wear.  Again, these are
> in-line (on a two dimensional plane) so there is  little danger of popping a
> belt off.  Our Corvairs' belts drive only the  fan and the alt/gen.  If there
> is an A/C compressor, it has its own belt  and it is in-line.
>
> On a final note, VV has many contributors who are real  authorities on
> technical topics as well as historical information as regards our  Corvairs and
> autos in general.  Many are very knowledgeable in off-topic  subjects as
> well.  I think we are all thankful for their  contributions.  I know I am.
> Unfortunately, there are a few  individuals who seem to feel that stating
> invalid information in an  authoritative manner makes them appear to be true
> authorities on a given  topic.  This is a sad reality in personal, business and
> political arenas as  well as here on VV.  Of course, they are entitled to
> their opinions as are  we all.  However, it is to our benefit to recognize
> these individuals as  being less than the experts they try to portray
> themselves as.  Once  identified, we can take their statements with a grain of
> salt.
> It  would be unfortunate if someone were to take misinformation as fact,
> apply it to  something important and live to regret it.
>
> Not to sound arrogant or self absorbed but you might say that  once you
> have read this clarification, "all will become clear."
>
> I would be happy to forward a link or links to sites which  show the
> numbers I have claimed above.  Just ask.
>
> Doc
>
> 1960 Corvette, 1961 Rampside, 1962 Rampside, 1964  Spyder coupe, 1965
> Greenbrier, 1966 Canadian Corsa turbo coupe, 1967 Nova SS,  1968 Camaro ragtop
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> In a message dated 4/11/2012 4:09:22 P.M. Pacific Daylight Time,
> virtualvairs-request at corvair.org writes:
>
> Message:  8
> Date: Wed, 11 Apr 2012 17:33:23 -0400 (EDT)
> From:  RoboMan91324 at aol.com
> Subject:<VV>  Fan belt tension
> To:  virtualvairs at corvair.org, cmckinley313 at verizon.net
> Message-ID:<7f08.772da2f5.3cb752a3 at aol.com>
> Content-Type: text/plain;  charset="US-ASCII"
>
> Hi Chuck,
>
> I don't recall seeing anyone  suggest a "very tight" tension on  a Corvair
> fan belt but I must  admit I skip some of the postings.  Always  tighten
> the
> belt so  you are just able to turn the alternator or generator fan  with
> one
> or two fingers.  You said, "just turn the fan" and I assume you  do  not
> mean
> the engine's cooling fan.  The engine fan has a  much larger  diameter and
> is
> much easier to turn even when the belt  is too  tight.
>
> If you over tighten the belt, you can shorten the  life of the  fan bearing
> (as you said) as well as the alt/gen  bearing, fan belt, etc.   However,
> there are other reasons to  avoid over tightening the belt as  follows....
>
> 1.  The  engine's cooling fan is a fairly large rotating  mass.  This means
>
> that it takes energy to spin it up to speed and once it  is at speed,  it
> is
> storing that energy.  In effect, it is a flywheel.    When you accelerate
> in
> first gear, you bring the fan up to speed.   When you  shift to second
> gear,
> the engine slows quickly (sometimes  very quickly) and the  fan tries to do
> the same but can only slow to  a limited degree.  Because  the fan wants to
> keep spinning while  the damper/crankshaft pulley has already  slowed,
> something must  slip, break or pop off.  Slipping is preferable to  the
> other two  and
> this is how the system was designed to operate.  It is   during the
> upshifts
> and to a certain degree, the downshifts that your belt  will  be more
> likely
> to pop off if it is too tight.  This is  especially the case  if you are an
> aggressive driver.  I believe  there is somewhat less risk of  this being a
> problem if you have an  automatic trannie.
>
> 2.  Pretty much everything expands as it  gets  hotter.  However, aluminum
> expands more per degree of  temperature rise than  many substances
> including
> steel.  As you  know, the Corvair crankcase and  other components are
> aluminum.   If your belt is a little tight when it is  cold, it will become
> too tight
> once the engine gets up to operating temperature  when the engine  expands
> and your belt could become far too tight if the engine   overheats for any
> reason.  You can see this if you check the  tightness of  the belt when
> cold and
> again immediately after you have  taken a drive.   (Don't burn your
> fingers.
> The alt/gen pulley  can also get quite  hot.)
>
> As a cautionary note, if you get general  service for your  Corvair at your
> local mechanic, check your belt  tightness when you get it  back.  Some
> mechanics are  conscientious and might check and tighten your  belt to what
> they
> think it should be.  Along this line of reasoning, you  should  also verify
> your tire pressure.  As you may know, our cars need   higher pressure in
> the
> rear compared to the front which is the opposite of  most  other cars.  The
> mechanic may think he is being thorough  raising the  pressure in the front
> but
> is actually creating a  dangerous situation in his or  her ignorance.  By
> all
> means tell  him but don't assume that just telling  the mechanic not to
> play
> with  the belt tightness or tire pressure is  sufficient.  The guy who
> "writes you up" may not be the guy who works on  your car or  FC.  I have
> also
> heard horror stories where the garage "helper"   tops off the Corvair's
> "radiator" with water.  You do not want to  drive the  car with a crankcase
> full of
> oil/water  mixture.
>
> Lastly, always carry a spare belt because you will be going  nowhere fast
> if
> you lose your belt.  It is cheap   insurance.  The belt is often torn up or
> permanently bent up when it  pops  off at speed.  You should also carry the
> proper tools to  replace the belt  but at least generic tools can be
> borrowed
> in a  pinch.  The proper size  belt may not be available where you break
> down
> on a holiday weekend up in the  mountains or in the desert  ........
> Murphy's Law.
>
> Doc
>
> 1960 Corvette, 1961 Rampside,  1962 Rampside, 1964 Spyder  coupe, 1965
> Greenbrier, 1966 Canadian  Corsa turbo coupe, 1967 Nova SS, 1968  Camaro
> ragtop
>
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