Why does my 350 keep burning out the bearings in my altornator?


Asked by Mar 04, 2018 at 10:52 PM about the Chevrolet Tahoe

Question type: Maintenance & Repair

I have a 1992 Chevy Blazer (Fullsize) with a 5.7L
350. About a year ago I had a horrible squeling
coming from the engine bay. Sure enough the
bearings in the altornator were shot. No big deal,
went to the part store and bought a new one.
About 3 months later, the same dam squeling
started up again. Sure enough the bearings in the
altornator were shot again. Took it out, brought it
back and they gave me a new one under warrenty.  
Ran good for another couple months and then the
same squelling came back!!! So brought it back
and got another. Well just my luck the bearings
went again!!!! That's 3 so far all with the rebuilt
status. Got angry and bought a brand new one
from a different part store I trust alot more. What
do ya know the squeling came back. Well no way
it's the altornator it must be something else. Took
out the AC replaced it with a simple pully. Replaced
the clutch fan. Replaced the tensioner and pully
along with every other pull and a new belt. Only two
things left are power steering and water pump. Still
have the squelling. Went out and bought new ones
and while installing I figured I might as well check
the altornaton and sure enough the shafts that
holds the fan and pully is bent.
IT'S BRAND NEW!!!!! When the squelling starts my
volts drop hard. The belt looks to be spinning freely
no problmes. No sings of slipping of belt wear at
all! Even if the altornator is not the squeling it
shouldn't be bent or of axis!!! I just find it hard to
believe that 3 rebuilt altornators and a brand new
one from a different part store are bad right from
the start. It now has me wondering if something on
the engine is destroying my altornators. Maybe too
much tension from the tensioner? (It has a spring
self adjusting tensioner so that doesnt make sense
and it's new) nothing makes sense right now. Does
anyone have any idea of what it could be? Help

10 Answers


Are you running the belt too tight?


I have a spring loaded tensioner on the belt so I cannot loosen or tighten it.


You probably can adjust the position of other accessories that would affect the belt tension. Another possibility is that you are buying junk.


I didn't think I could adjust the position of the accessories so i never considered it. I will look into it tomorrow. Thank you

1 of 1 people found this helpful.

Ok so I'm looking at my engine and I can't adjust the position of any accessories. I just picked up my 5th alternator witch is the exact same as the one I returned, brand new. In terms of quality I can't buy a better one. Unless I go into some rediculous high end performance modle witch would be useless seeing as my engine is stock. Maybe I have been cursed with bad alternators. If my truck requires an altornator with an output of 120 amps but I install an altornator rated for 100 amps (Witch seems to be the one I need), would that burn it out?


Update to my problem. I have a brand new altornator, water pump, and power steering on, all with 10 seconds running time on them. The dam squeling is still there!!!!????? Maybe one of the pully's I pot on is bad? Maybe the main bearing? When the squeling starts my volts drop like the altornator stops charging. No signs of belt slipping. The other accessories are not hooked up to electrical. If the main bearing in the engine was shot would that slow down the altornator enough for the volts on my batterie to drop?


Just thinking. If the main bearing was shot it would slow down the rpm of the engine, in turn slowing down the altornator and all my accessories enough to drop the volts on the batterie?


Absolutely not to the main bearing on the engine... Have you replaced the spring loaded tensioner? To your original question about bearings, have you checked the grounds that are attached to the engine? If an isolated engine/transmission is not fully grounded, this is possible. And one easy way to make sure...run a new ground from frame to engine. Can't hurt.


Ya your right, it's not the main bearing. Yes I have replaced the spring loaded tensioner. Actually no, I haven't checked the grounds attached to the engine from the frame. It is very possible it is not grounded at the moment. Tomorrow I will check all the grounds, and like you said, run a new ground myself to make sure that the connection is not faulty.


If you get it back going, with ground and all, idling...add a little slight, steady force to the tensioner with a pry bar...(yes, I did read that you replaced said item, but I too just went thru this on similar situation with AC idler on Silverado...cheap idler...didn't last 5 minutes, and exploded). If this seem to help, and doesn't seem like too tight a belt...buy a new shorter belt, by a few millimeters...This is easier to do that you think, and it only take 4 to 5 millimeters to make a substantial difference.

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