<VV> Fan belt tension

Wed Apr 11 17:33:23 EDT 2012

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

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In a message dated 4/11/2012 1:27:58 P.M. Pacific Daylight Time,  
virtualvairs-request at corvair.org writes:

Message:  1
Date: Wed, 11 Apr 2012 12:03:53 -0400
From: chuck mckinley  <cmckinley313 at verizon.net>
Subject: <VV> Fan belt  tension
To: VirtualVairs AA <virtualvairs at corvair.org>
Message-ID:  <1334160233.1878.10.camel at mingus>
Content-Type: text/plain;  charset=UTF-8

Speaking of fan belts, I'd like your thoughts on correct  tension. I've 
seen very different ideas on this, from very tight (at the risk  of rapidly 
wearing out the blower bearing) to loose enough that you can just  turn the fan 
by hand with the belt installed. I've tended to use the latter  approach, 
as it makes sense, and there's still enough friction to turn the  generator. 
Comments?

Cheers,
Chuck McKinley
'63 Monza  900