<VV> Fan Belt Experience
Sethracer at aol.com
Sethracer at aol.com
Tue Jul 2 01:44:09 EDT 2013
Okay - My two cents. On Sunday I went through a day of Autocross belt
problems. This experience will be applicable to only a few folks. You will see
why. On my race motor, I am running one of the LeVair half-speed fan kits.
The kit replaces the drive pulley with a smaller pulley that bolts to the
center of a disassembled late model dampener. (They is a good supply of
these, by the way.) The system also uses a larger pulley at the fan. There is
also a modified mount to provide a better alignment for the alternator and
the idler pulley. The two changes of the pulleys offset each other and the
design uses a stock-length fan belt. I ran the complete set-up at a track
event and a bunch of autocrosses last year with no belt problems. I have been
using a Corvair Underground spring loaded idler as well. At the last event
of 2011, I ran several runs, the last of which, it turns out was without a
belt. Due to my negligence the idler setup had come adrift, followed
shortly by the belt. Continued running loosened up a valve seat, and the season
was over. In preparation for going to Kalamazoo, I prepped another 140, and
moved the belt drive system over - except for the belt, which had been
damaged, I used a new Clarks HD belt. I re-assembled the Idler, assuring that
it would not come loose. Now I wanted to make sure the car would work for
the long-haul back to Kalamazoo. In an event two weeks ago, I had no
problems, but the small lot didn't really tax the systems, really no shifting. On
Sunday we ran a fast, fun event at Marina, top of second gear for me and a
few shifts. On my second run, the light comes on, the belt had departed. I
installed a new identical belt, lubed the crap out of it - and it came off
at the first shift. I cruised slowly back in, put the seemingly undamaged
belt back on, ran my fourth run - actual 2/3's of it, Light on, shut off.
After I brought the car back to the pit area, I put the belt back on, hitched
it up and towed home.
I talked a bit with Warren last night, we went over the possibilities. He
is running the exact same set-up. He mentioned one possibility, the belt,
when restrained by the idler, is pulled back to the rear of the car a bit
more than vertical. He said that both he and Michael had found that whenever
the belt is leaning back from vertical, there is a tendency to come off. A
wider belt might functionally run as a longer belt, because it would ride
higher on the pulleys. One other note, I was running an early version of
the Underground idler. I also had a new one sitting on the shelf. The spring
in the pulley on the newer ones is definitely longer (stronger?) that the
This morning I removed the idler and swapped the heavier spring on. I went
through the dozen or so fan belts, looking for a shorter one. The Current
Clarks HD and their Otto Parts Super belt were all the same length, allowing
the belt to lean backwards. I did have new pair of older Otto Parts belts
marked C8704. They are definitely shorter and, when installed, feed
vertically up to the idler.
In the past, I have run the Gates 3VX560 belt (Notches on the bottom) and
the Dayco Top Cog belt. Those are listed as 56" length belts. I noted that
both of these belts are available as 55" lengths as well. This morning I
ordered one of each and they will be the next test.
There is another Autocross this Sunday at Marina. If the belt survives, the
car goes to Kalamazoo!
The jury is still out on whether the belt length is THE factor. We shall
see. - Seth Emerson
In a message dated 7/1/2013 7:01:39 P.M. Pacific Daylight Time,
RoboMan91324 at aol.com writes:
I believe that the only time a properly adjusted belt will slip is under
high acceleration/deceleration conditions on the motor RPM. This happens
during shifts. The motor changes RPM very quickly at these shift points.
You want the fan to slip a little at these points or the fan belt will be
more likely to fly off. Unless the belt is too loose, I don't think the
will freewheel other than the mentioned accel/decel situation. This is
especially the case when everything has warmed up to operating levels.
the belt and pulleys are warm/hot, the contact friction increases. Also,
engine will have grown due to thermal expansion.
Just my opinion,
1960 Corvette, 1961 Rampside, 1962 Rampside, 1964 Spyder coupe, 1965
Greenbrier, 1966 Canadian Corsa turbo coupe, 1967 Nova SS, 1968 Camaro
In a message dated 7/1/2013 4:51:52 P.M. Pacific Daylight Time,
virtualvairs-request at corvair.org writes:
Date: Mon, 01 Jul 2013 15:16:18 -0700
From: Bill & Chris Strickland <lechevrier at q.com>
Subject: Re: <VV> Fan Belt Physics
To: virtualvairs at corvair.org
Message-ID: <51D1FFB2.5060603 at q.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
> Belt is too tight! When the engine is COLD...using your HAND ONLY pull
back on the idler/ tensioner pulley.. lock it and leave it..
> You should be able to slip the alternator fan with a finger...
Well, that is one opinion and it seems to work for lotsa folk, but it is
not the only opinion. I don't like the idea that I could be loosing a
of cooling air in an already inefficient system by fan belt slippage due
the belt being too loose.
Fan belts are now made a lot tougher than they were in the sixties -- use
good ($$$) belts!
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