<VV> Fan belt tension

Wed Apr 11 20:17:26 EDT 2012

 The belt expands thermally about 10x that of any of the metals the engine is made of. It'll get looser as it gets warmer. Check your CTE tables for polymers, and all will become clear. 

The belt has problems because of the design. Stick shifts make things worse. Looser belts stay on better, but wear out faster. That around the corner thing might be fine for an econo car, but run a turbo to redline a bunch of times, and, well, the result is obvious! After all, the fan on a water pumper is WAY more massive than a Corvair fan, and they stay on, even without the viscous clutch! 

John Roberts

-----Original Message-----
From: RoboMan91324 <RoboMan91324 at aol.com>
To: virtualvairs <virtualvairs at corvair.org>; cmckinley313 <cmckinley313 at verizon.net>
Sent: Wed, Apr 11, 2012 7:09 pm
Subject: <VV> Fan belt tension

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

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