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GM Alternator- reverse direction and cooling


ARUCKEY
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I have added a GM V-8alternator to my 1938 Nash. After installing, I realized that the cooing fan on the alternator just behind the pulley is turning in the wrong direction. I found that it is ok to run the alternator in this reverse direction and will still put out 12 volts. I understand some marine engine run in the reverse direction compared to cars. Looking for a replacement fan with reverse direction fan blades. Someone mentioned 1965-69 Corvair ran in reverse direction.

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Some cars with flat belts drive the alternator backwards. Corvair engines run backwards to all normal engines. Try your local auto electric shop, they probably have a box full of pulleys and fans under the work bench and can fit you out with a better fan.

Does your Nash have a conventional V belt drive alternator? It sounds like you got one of the odd reverse rotation alternators when you need a conventional one.

The fan is arranged to draw air in the back of the alt and out thru the fan.

Edited by Rusty_OToole (see edit history)
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This alternator is from a Chevy V-8 engine and is designed to run in a counter-clockwise direction. It is now running in a clockwise direction on my Nash engine 6 cylinder engine and the fan behind the pulley is not pulling air through the alternator.  I am looking for a fan that is designed to be used on some marine v-8 engines. These engines rotate in a clockwise direction.  Obviously not all marine engine are set up to run that way, only certain applications.  In the end I may just cut of the blades and weld them on in the opposite direction.

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The alternator innards do not care what direction the shaft (field in this case) is turning.

 

But the cooling fan does. Or more to the point, the innards care if they get cooled properly!  In the Corvair world, many people buy the later internal regulated alternator from the 70s and 80s, and they just swap the front housing (because of an odd mounting pattern on the Corvair) and the fan to the replacement alternator. You just have to swap the fan. 

 

Try one of the Corvair vendors, like California Corvair Parts or Corvair Ranch in Pennsylvania for a used fan.

 

BTW, to swap the fan, you need to hold the shaft with an Allen wrench (5/16 IIRC). DO NOT hold the fan by the blades, they will bend.

Edited by Frank DuVal (see edit history)
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  • 2 weeks later...

Nope, the GM alternator has a hex in the shaft, so the pulley and fan can be removed with hand tools. 

 

I do agree, the generators need an impact gun, as holding the fan blade is just going to bend the fan blade. DAMHIK.😁

Alternator Nut Removal and tightening.jpg

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Almost all alternators are set up for clockwise rotation. About the only Chevy application that is set up for CCW is Corvair. But you may be mistaken. The fan is designed to pull air from the rear through the alternator and exhaust it through the front. Yes, this is counter to the natural airflow direction. But the reason is that the fan is there to cool the diodes and regulator, which are in the back of the unit.

 

The only front engine cars that I know of set up for reverse rotation are Jaguar E-Type and Honda Prelude. But there are a LOT of aftermarket parts available for Delco alternators, including omnidirectional fans, generally used for marine and aviation applications. There's more on this in my writeup on E-Type swaps:

 

https://www.coolcatcorp.com/faqs/LucasBosch.html

 

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