<VV> Fan Belt Physics

Ron ronh at owt.com
Tue Jul 2 00:28:38 EDT 2013

If the pulleys didn't feel hot, then the belt wasn't hot as the pulleys are 
the only way to heat the belt.  Head temps have nothing to do with it except 
when shut down.  When the engine is running, everything on top of the shroud 
is very close to ambient temperature which is the temperature of the cooling 

----- Original Message ----- 
From: "kevin nash" <wrokit at hotmail.com>
To: <virtualvairs at corvair.org>
Sent: Monday, July 01, 2013 8:44 PM
Subject: Re: <VV> Fan Belt Physics

>> Message: 7
>> Date: Mon, 1 Jul 2013 16:51:36 -0700
>> From: "Ron" <ronh at owt.com>
>> Subject: Re: <VV> Fan Belt Physics
>> To: "Bill & Chris Strickland" <lechevrier at q.com>,
>> <virtualvairs at corvair.org>
>> Message-ID: <FEA72EDCB1CE42D79F3BC8F82488E373 at YOUR76500D519C>
>> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>> reply-type=original
>> Is there any slippage that anyone has ever documented or is it just 
>> another
>> theory?
>> RonH
>> Ron- The way most of us set our belts, (light finger pressure to turn the 
>> alternator), yes there quite a bit of slippage at 4000
> rpm- a guy posted this on the fastvair board. He used the tach off of his 
> sds (digital tach to measure engine rpm) and measured
> the fan rpm with a optical tach- there was no slippage with the damper 
> doors shut, but with the damper doors blocked open,
> he was reading 600 rpm lower. Pressumably, he did this with the engine 
> cold and not hot (theres  less pressure for the fan to push
> against when the engine is hot)- however, he did not try doing the test by 
> setting the belt as tight as GM wanted, which was
> 75LBS(!) belt tension set with a belt tensometer. Set that way, I 
> seriously doubt there's any slippage  ( although I intend to
> do that test once I get finished with another project that I have to get 
> done). Once, many moons ago, I did probably come close
> to setting the belt that tight- I know it was just about so tight so as to 
> turn the engine over with the fan (oops- I didn't know any better!)- 
> anyways, the belt came off on one shift at 6500 rpm- never set it that way 
> again. Anyways, I have measured shroud pressure with the engine good and 
> hot, and found ZERO difference in pressure when the belt is set normally 
> vs scary tight.
> Also, I actually did verify what JVH said about the belt expanding more 
> than the engine does hot vs cold, the belt really does
> get significantly looser when the head temps get to 300 degrees vs dead 
> cold. I measured the belt deflection at 1/2" when cold
> and then when the head temps got to 300 degrees, measured the deflection 
> at "very close" to 1"- I do have aluminum pulleys
> on my car, which might have something to do with it (probably very little, 
> as the pulleys didn't feel very hot when I touched them).
> I also bothered to re-check the deflection of the belt after the engine 
> was back to dead cold again, just to make sure that the
> the idler hadn't slipped, and... the belt droop was back, as best I could 
> tell, where it was when I initially set it to 1/2"
> Kevin Nash
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