<VV> Do Gen Pulleys Lose Their Grip?

Tony tonyu@roava.net
Thu, 20 May 2004 16:40:11 -0700

At 1439 05/19/2004 -0400, goofyroo@excite.com wrote:
> I have a modern (7127) alternator installed on an early with a custom
bracket.  It uses the original generator pulley.  The system works fine until
you put a really, really heavy load on the alternator (AC with condenser fan),
then the voltage starts dropping.  

Not entirely unexpected.   What *is* the rating on your alternator?   And how
much does the voltage drop?    

>An alternator rebuilder, whom I know and trust, says the unit checks out
fine.  (I had replaced the diodes, regulator, and brushes in
He says the belt is probably losing grip.

Do you hear any shrieking or chirping noises?   One way is to simply watch the
alternator with the engine running with a heavy load while you rev the
engine.    However, it's gonna have to be slipping a LOT to drop the voltage
enough to become an issue.   

>When you look at it, on a Corvair the belt only grips the gen/alt and idler
pulley over about 1/4 of the pulleys' circumference.  Unlike on other engines,
where the belt contacts about 2/3 of the pulley.

However, a lot of people have been running standard alternators with AC and
other accys all on at the same time and no real problems.   

>Any thoughts on what might be done to improve the grip?  I have tried
tightening the belt, using a "cogged" belt, and loosening the belt, to no

It's been my experience that the belt needs to be relatively loose in order to
stay on the engine unless you never rev the engine to any degree...  better
luck is had with Powerglide cars than manual shift cars.   

I'd work with a smooth polish on the pulley and use a cut belt...  IF the
alternator pulley is actually slipping.   The standard cut belts will bulge
slightly when pulled around a corner and grip the pulley tighter.  A cogged
belt will not.   The cut belt on a polished pulley is gonna give you the
tightest grip you can expect without excessive belt wear.    

I'd also check out the wiring, especially the heavy wire from the
alternator to
the battery + terminal.   If that wire has a less than adequate connection on
either end, voltage drops could become evident, along with hot connections.

There are sharper people in here than me, who likely will have better
information for you but this is what I've seen in my times.