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Discussion Starter · #1 ·
I just replaced my 64 amp 10si with a 94 amp 12si alternator. I also replaced the V-belt and upgraded the size of the charge wire. The engine is a GMPP 350 with the stock '75 drive belt system.

The rebuilt 12si alternator seems to make quite a bit more noise, and I'm not sure if its just the larger cooling fan on the alternator, or if there is something wrong with it.

I get a noise that sounds like drive belt squeal when I start it up cold, but its not the belt slipping - is it bearings in the alternator? Is there anywhere I could put a little lubrication on the bearings?

It also sounds like my engine fan (HD clutch fan) is making more noise, but then I realized it might the fan on the alternator. I assume this is normal?

Thanks,

Bruce
 

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whats the output??

I have heard this before on vehicals of my own. It doesn't necessassarily mean anything is wrong. you have steped up in charging capacity and some noise is normal. As far as oiling the bearings??! Not possible. You would have to tear the alt apart to access the bearings.I'll tell you a an easy way to check the alt and charging system. First remove the alt belt,lay your hand on the alt and spin it with the other hand, you shouldn't feel any roughness or here any growling. Next reinstall the belt making sure to not over tighten as this will cause noise as well. You can buy what is called a cricket gauge to check the proper belt tension. Next crank the engine and turn on all lights and accessories and check what the voltage is at the battery with a digital volt ohm meter. It should maintain at least 13.5v with all lights and accessories on and should not exceed 14.7 volts under no load at idle. If voltage is low make sure all connections are clean and tight on all points in the charging system and all ground connection points are clean and tight. you will have to remove the connections to verify there isn't hidden corrosion. If this doesn't resolve the issue post it again and we'll go over it again and see if we can figure it out. hope this helpd thanks Brian :cool:
 

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You may want to remove the alternator and loosten the screws that hold the 2 halves together, rap it a few times with a rubber hammer and put it back tighten them back down. My buddy used to have an alternator and strarter rebuild business and I saw him do this many times on the test machine.
 

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Doc here, :pimp:

If you rebuilt the alternator, you may have an issue with spinning bearings under load..

The End-bells will wear to the old bearing diameter, and new installation of bearings will be slightly undersized.

Whenever rebuilding these units I always advocate using a very small center punch and placing a "Dimple " each 1/3 the way around..this way once the end~bells are attached, the bearings Can Never spin.

Do not attempt to oil the bearings. For one, they are perma~lubed, and sealed..If you break that seal, they will allow dirt in, and the bearing will just burn right out..(within a few days) . And Two, if you do get a lubricant in there it will just melt out and splatter all over the interior of the alternator, insulating the slip rings , and causing shorts.

One other probability exsists..if you put the slip ring brushes in counter to the Arc in the slip ring OR if you didn't hold them all the way off the slip ring while installing the end bell, they could have snapped with a flat surface on the slip ring, making noise.

Doc :pimp:
 

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Discussion Starter · #5 ·
The 12si alternator I installed is a rebuilt Delco alternator from Advance Auto, which sells it under the Palladium brand name.

Voltage output appears fine on the new alternator, since it maintains about 14 volts at idle with the headlights on and the heater fan on high. This is a major improvement from the old alternator I replaced.

The startup noise/squeal seems to be going away, so maybe the bearings are okay. I need to give a few more days and see if there is any change.

Bruce
 

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Doc here, :pimp:

OK, another thing it could be, on some of those new / Rebuilt Alternators, is if the Groove for the has just the slightest bit of paint on it, or is super smooth, they will slip until the belt and pulley wear into one another..

If you have a lot of paint (anything more than overspray) a lot of times the belt will just snap within the first few minutes or run time..(had it happen several times!)

Doc :pimp:
 

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Discussion Starter · #7 ·
Doc,

You might have the right answer.

This rebuilt alternator snapped the old belt in the first minute after startup and I had to make a run to buy a new belt. I assumed it was just time for the old belt to go, but maybe it was related to the pulley on the rebuilt alternator.

The pulley isn't painted. Its a very bright and shiny metal finish, and I wondered how well the old belt would grab on the smooth surface. The alternator may have been grabbing unevenly until some of the shine wore off the pulley and the belt took a set into the groove.

Bruce
 
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