New Alternator Whine/Whistle

[Yatzee]

There are a couple of issues that could cause this noise. Serpentine belts need to track exactly straight with pulley alignment or they tend to sound just like a high pitch whistle. With the new alt mounted and spinning at about 1700 r.p.m. take a squirt bottle and squirt water on the belt just before the alt pulley to see if the noise subsides. If it does then the position of the new alternator is farther ahead/behind where the original alt sat and needs alignment. It may also be cocked and on a bit of a slant. If that does not prove fruitful then the bearings could be at fault and may be of cheap quality. There shouldn't be much in the way of end play if any at all. Some new alt's whine as the brushes which are flat on their tips wear into an arc to match the armature but not that loud. To my knowledge proper bearings should match the speed and side load of the conditions they operate under and I fear yours don't. The alt may have sat around too long before selling and the grease in the bearings has gone a bit dry.

 

[bigmanjbmopar]

Wonder if you over tightening the alt in its bracket if you can be putting too much side force on the pulley making it get a hair off inside? seems unlikely but if the bearings are poor quality maybe?

 

[Yatzee]

That's exactly correct. Some bearings are meant for radial loading and some for axial loading. Timken style roller bearings will do both but are not of the high speed type. When you side load a radial roller bearing, there is no lubrication on the sides of the races so basically the bearing is running dry on the area where the balls travel. I hardly doubt that the alt was not tested before marketed and I would suspect that the manufacturer uses the same brand bearings for all units. You know there's no magic to upgrading the bearings in the alt if you can't return it. If you do, use precision bearings from a supply house that are meant for radial and axial loading and/or thrust - NSK, SKF and FAG brands come to mind. These are a bit pricier so I doubt you'll find rebuilders using them after all they want you coming back right?

 

[rebootej]

The third replacement made the same noise. Still does. Ill have to try your water trick yatzee, It looks pretty straight but it would make sense that something is up with the alignment since all 3 have done it.

 

[bm02tj]

Or they all have the same brand of bearing

 

[rebootej]

Possible but weird all 3 would do it but when i put the old one it an autolite the noise goes away

 

[bm02tj]

Try it with the wiring removed and taped then loosen the belt and if still noisy it is bad bearings
remove belt and spin by hand and listen and feel
if any noise or roughness bad bearings or poor quality