All Small Six 76' i6 250 w/AC - Alternator Belt keeps squealing and snapping

This relates to all small sixes
M

MavChick76

New member
76' maverick - i6 250 w/AC (links in paragraph to parts used)

The V-belt that is connected to my alternator/water pump/crank shaft keeps squealing. I have practically replaced everything and can not find the main issue.

The car is a surviver so everything including the engine is almost all original. At first I noticed the water pump pulley was slightly bent.

The original part number for my pulley was D3DE 8509 AA. This is a 2 groove pulley that connects the water pump to both the alternator and A/C. I could not find another exact match for this 2 groove pulley, but I am currently not using the A/C and that is what the groove closest to the fan was needed for. So instead of getting an exact replacement of D3DE 8509 AA I got C9ZE-8A528-C which is the 1 groove version the original pulley.

Once I know I had a straight pulley I put it back on the water pump but still saw some slight walking which lead me to believe the water pump shaft may have also been bad? I went ahead and replaced the water pump to be safe. After this the pulley seemed to spin straight on the shaft just fine.

Drove it after these fixes but it still started to wear the belt and squeal after around 30-40 minutes of driving.

The only thing left I could think was that the alternator was bad or causing resistance so I replaced the alternator as well. I know it is not the crankshaft pulley because that is connected to the power steering and I have never had any issues with those pulleys/belt. After replacing the alternator I was able to drive it for hours before the squealing started to slowly pop back up again.


Any Idea on what could be causing this?? I am at a loss. The only other thing I can think of is to get a slightly smaller belt so it fits inside the grooves of the alternator lower but I have seen mixed opinions on doing that.


I don't have a video with the squealing happening because when it's first starting it comes and goes but here is a video of it running before I had replaced anything:
https://drive.google.com/file/d/1dv1GF0rFvFZlJ0P6bZ-OOcB3J0hOQq7H/view?usp=drivesdk
https://drive.google.com/file/d/1k01OmQX9NsVqnrvQnc5Q3aoK4NWqX5OZ/view?usp=drivesdk

And here it is with the new pulley/water pump/alternator (and yes the belt is very loose in this video because I have not adjusted the tension of it after it started squealing again):
https://drive.google.com/file/d/1GRHl_Uua_4-hyCouhlSoYTEJVa0gkj3D/view?usp=drivesdk
 
Is the bracket at top of alternator bolted firmly to block? Looks like some movement there when revving up.
 
with engine movement it is difficult to tell, also considered alt bracket and bottom bracket and block fasteners integrity...
.
.
 
Hi, my first guess is that the belt is too narrow for the water pump pulley. The inside of the V belt should not bottom out on the pulley. The belts are designed to ride on the sides of the pulley. I would try a thicker belt. Google a V belt thickness chart. The belts use a letter size. Good luck
 
So I am curious, this just started happening and there had not been any one working on the vehicle? Taking the belt off the smog pump etc?
And the Mav had been running/driving fine?
 
bmbm40 said:
So I am curious, this just started happening and there had not been any one working on the vehicle? Taking the belt off the smog pump etc?
And the Mav had been running/driving fine?
Click to expand...
The car had been sitting for about 40+ years untouched and when we pulled it out of the mud we had to replace a few things (the water pump and alternator being one of them). This has been an issue since we have had it running. Besides for this issue it drives perfectly. after messing with it for some time now I am pretty sure the issue is the alignment of the ALT pulley.

The water pump and harmonic balancer pulley are perfectly aligned but the ALT pulley is about 1/4-3/8" too far forward (toward the radiator). Any idea on next steps for this?

link to Photos/Video folder of alternator connected to brackets on engine:
https://drive.google.com/file/d/1HL6_N0Y-S0qJHfNl9phss_r9OZMjluY9/view?usp=drivesdk
 
MavChick76 said:
The water pump and harmonic balancer pulley are perfectly aligned but the ALT pulley is about 1/4-3/8" too far forward (toward the radiator). Any idea on next steps for this?
Click to expand...

I would remove the alternator mounting bracket and redrill/file/elongate the block mounting holes into slots. This way you can slide the bracket back and forth until the pulley is perfectly aligned, and then snug it down tight. The top bracket can either be bent, or, just use a couple washers as spacers.

50+ year old cars = mods for adjustment.

The thick shouldered double pulley isn't helping, either. Swapping to a thin shouldered stamped steel pulley -might- give move the belt plane back enough to run without problems. You'd need an impact wrench to do the swap, and, an old style pulley. Even then, you still might not gain enough to cure the misalignment.

Cut slots.

Rick(wrench)
 
rickwrench said:
I would remove the alternator mounting bracket and redrill/file/elongate the block mounting holes into slots. This way you can slide the bracket back and forth until the pulley is perfectly aligned, and then snug it down tight. The top bracket can either be bent, or, just use a couple washers as spacers.

50+ year old cars = mods for adjustment.

The thick shouldered double pulley isn't helping, either. Swapping to a thin shouldered stamped steel pulley -might- give move the belt plane back enough to run without problems. You'd need an impact wrench to do the swap, and, an old style pulley. Even then, you still might not gain enough to cure the misalignment.

Cut slots.

Rick(wrench)
Click to expand...
Thanks! I like the slot cutting idea!

Right now I am waiting for a slightly higher quality alternator to come in to switch to a 1 wire and see if the measurements are any different on it. If they aren't I will probably go forward with cutting the slots.
 
The Mav may have been parked because of this same problem or, most likely, there was a difference in the replacement parts and if you don't have those original parts to compare then you rely on mods and suggestions as stated elsewhere/previously. Stating the obvious, sorry. So the mechanic for the alt replace is a known qualified mechanic? Did the replacement alt come with pulley attached? It was a rebuilt most likely and could have been sent out with an incorrect pulley attached. You are getting good advice from very qualified members (way more than me) so it will get resolved.
 
bmbm40 said:
The Mav may have been parked because of this same problem or, most likely, there was a difference in the replacement parts and if you don't have those original parts to compare then you rely on mods and suggestions as stated elsewhere/previously. Stating the obvious, sorry. So the mechanic for the alt replace is a known qualified mechanic? Did the replacement alt come with pulley attached? It was a rebuilt most likely and could have been sent out with an incorrect pulley attached. You are getting good advice from very qualified members (way more than me) so it will get resolved.
Click to expand...

As of recently I am/have been doing all the repairs and replacements myself with the help of my qualified mechanic roommate. And yes the new alt came with the pulley already attached but I have compared multiple of this specific Alt and that is just how the pulley comes.

After I get in a higher quality alt, if the alignment is still an issue, I plan to slot out the alternator brackets connected to the engine as rickwrench suggested.
 
If you have the lowet bracket off, it would be interesting to see part number. I wonder if it's the wrong one. I think the 250 and 200 spacing is different, and wp height too
 
comet6 said:
If you have the lowet bracket off, it would be interesting to see part number. I wonder if it's the wrong one. I think the 250 and 200 spacing is different, and wp height too
Click to expand...
I highly doubt that the brackets are the wrong part number. Everything in this is practically 100% original except for the alternator and a few other thing s i replaced.

But unfortunately I cant’t see the part number on it right now.
 
So, the new alternator's pulley is out of line with the other two pulleys. If you still have the old alternator, does its pulley line up with the others?
 
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