It didn't really explode, just shed all of the plastic fins. I have an 86 GT with a LS1 swap that was installed using an Archie kit. It has the stock SI type alternator. Problem is that I have had 2 of them break off all of the plastic fins for the fan. The first one failed shortly thereafter. I am just waiting for the second one to die. The first was replaced under warranty but I don't want to have to change it every few weeks. I asked Archie and since he never heard of this problem, he didn't have any advice. I don't think it is hitting anything and don't see any damage on the firewall or nearby components. The only thing I can figure is that the engine pulley on the LS motor is quite a bit larger than the v6 so the alternator turns to fast. The Fiero alternator pulley is smaller than the Corvette alternator pulley that came with the engine.

Has anyone ever had this happen? Any advice?

This weekend I am replacing the struts, plus changing the cradle and rear control arms to poly. While I was at it, I was thinking about doing the CS alternator upgrade. I was going to use one from a 90's big block truck that has the larger 6 groove pulley. This also has metal fins on the fan. I am hoping this will solve the problem but I am seeking advice if there is a better alternative.

Thanks in advance -
James

if you think its over-rev'ing then replace the pulley on the alt with a larger one? also maybe try some metal blades?

I have had this problem before, installed (3) rebuilt alt before I got a decent one. Each had inturnaley exploded within a day or two of installation. Just kept returning them until I got one that lasted the last 10 years so far. Just bad rebuilds.
The were from NAPA
My sympaties been there.

Is this a 12Si with the smooth front external fan behind the pulley? Is the belt rubbing the fan?

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1986 SE Aero coupe.

3.4 DOHC swap is complete and running, now just have to finish the rest of the car...

Check to see if the pulleys ARE lined up properly.

I'd swap in a CS130 alternator. They were on the 88 Fiero.
https://www.fiero.nl/forum/Forum2/HTML/127379.html

I have them on my GT and my Indy.




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Calgary time/temp

3.4L Supercharged 87 GT Click me
Super Duty 4 Indy #163 Click me

[This message has been edited by fierosound (edited 02-28-2014).]

Metal fans won't fix over rev'ing problem. Plastic fan is early warning the alt can/will die soon.
Using CS130 won't help either.
You need correct alt pulley for crank pulley.

alt to crank pulley size ratio sets Alt's RPM.

If use small WP pulley then OE for this engine then will cause problems is cooling system.
WP will have problem from cavitation, even destroy the WP, by over rev.

if both are small... then maybe use smaller crank pulley.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

You should try to keep the max alt rpm at 15000 rpm. To figure that out multiply your motor rpm times your pulley ratio.

For tight installs and higher rpm motors we use a honda alt converted to one wire, their about the side of a orange and 1/3 the weight of a gm. you can buy them fairly cheap and they take heat better than a v6 gm alt. and they will spin the higher Revs no problem too. and any Gen/ALT rebuilder can change the amperage to your choice for a couple 20s

Thanks for all of the replies and advice. I think I will go with my original plan and install a CS130 type from a truck. This will have a larger pulley and a metal fan.

-James