Alternator/Water pump belt vibration

Stevehose

Stevehose

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An annoying vibration has cropped up, between 2200 and 2800 rpm the alternator/water pump belt starts to flap a little which I can feel in the accel pedal. I can rev it in neutral and watch the belt section between the harmonic balancer and the water pump start to flap, then it goes away at higher or lower rpms. I had an alternator alignment issue before but I bent the mounting tabs to straighten it out, and there is no flapping or unusual movement of the belt over it's pulley. Here's what I have so far:

New (shorter) alt belt - no difference
Change in belt tension - changes the rpm vibration/severity range slightly
No visual wobble of the balancer or water pump pulleys
Don sent me a balancer which I installed last year.
Balancer and water pump pulleys appear to be in perfect alignment

If the alternator were still out of alignment, why would the flapping occur between the balancer and the water pump as this is the shortest length of belt?

Any ideas? TIA.
 
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Alternator is brand new installed before the Vintage and has no bushings (same as my original and previous 85 amp one), bolts between 2 tabs on a bracket on the block. And if it were bad, would this manifest itself with belt flapping between the harmonic balancer and the water pump?

Ohmess said:
Have you checked the alternator bushings?
Click to expand...
 
Is the alt tight where it bolts to the mount? Even though the alt has no bushings, there should be no clearance at either end of the mount. You may have to run a washer or shim between the bracket and the alt. Hope this makes sense to you


Thanks, Rick
 
Maybe check if all pulleys on engine are ok (not distorted). Or if water pump bearing don't have any slack.
 
Yes the tabs are tight and the alt is snug without even tightening the 17mm bolt.


stphers said:
Is the alt tight where it bolts to the mount? Even though the alt has no bushings, there should be no clearance at either end of the mount. You may have to run a washer or shim between the bracket and the alt. Hope this makes sense to you


Thanks, Rick
Click to expand...
 
I checked for water pump bearing play but could not detect any, the pump is a year old.

All pulleys look good when viewed in motion.

Strange...

Wladek said:
Maybe check if all pulleys on engine are ok (not distorted). Or if water pump bearing don't have any slack.
Click to expand...
 
Check the 36mm nut on the crank. When it is loose, this annoying problem happens.
 
crank nuts...I hate crank nuts...

I will run briefly without the belts to test per Don then look at the pulleys, would the crank nut still act up if not under tension from a belt, and should I break the nut and retighten or just tighten?

Thanks.

Vern said:
Check the 36mm nut on the crank. When it is loose, this annoying problem happens.
Click to expand...
 
****UPDATE***

It appears that the alt belt is wandering slightly back and forth in the water pump and balancer pulley grooves at various speeds, more noticable in the balancer pulley and less so in the water pump pulley. The PS belt doesn't appear to be wandering in the groove of the water pump pulley. The balancer doesn't appear to wobble and I installed the crank nut last year when I did some lower end work so I don't think it's loose but I will check it due course.

So then I put the AC belt back on and sure enough the alternator belt wanders in the balancer pulley but the AC belt does not which tells me this pulley is ok?

Therefore I am going to examine the alternator again to make sure it is feeding straight into the crank, since this has been a previous issue. Gremlins piss me off!
 
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Stevehose said:
****UPDATE***

It appears that the alt belt is wandering slightly back and forth in the water pump and balancer pulley grooves at various speeds, more noticable in the balancer pulley and less so in the water pump pulley. The PS belt doesn't appear to be wandering in the groove of the water pump pulley. The balancer doesn't appear to wobble and I installed the crank nut last year when I did some lower end work so I don't think it's loose but I will check it due course.

So then I put the AC belt back on and sure enough the alternator belt wanders in the balancer pulley but the AC belt does not which tells me this pulley is ok?

Therefore I am going to examine the alternator again to make sure it is feeding straight into the crank, since this has been a previous issue. Gremlins piss me off!
Click to expand...
I dunno Steve, sounds like some voodoo Louisiana curse or something, anything we should know about?
 
I think you're right, Marie Leveau or something . I swapped out the crappy looking 2 piece alternator pulley that came on my recent 85 amp alternator (didn't realize it was a 2 piece till today) for my old solid one piece one. Big improvement but not 100% gone, its now mildly annoying down from very annoying so i think i may be onto something. I will look at the geometry a little more. Gary, it's the serrated belt, and the recommended 9415 belt number, although i put a slightly shorter version on to minimize slack (9412). Is there a difference with the non-serrated?

Are there any black magic tricks to aligning pulleys other than a straight edge? I think this is where i will focus next.

Don, this is an upgraded alternator from BNR and i have the 9 blade fan and fan clutch with the hole in it.

Thanks for the suggestions.


bluecoupe30! said:
I dunno Steve, sounds like some voodoo Louisiana curse or something, anything we should know about?
Click to expand...
 
Start the car cold with fan removed
Remove AC fan belt
Remove PS belt
Fire it up and tell us what you see

Those fans I like are back in stock (15 bucks) at rmeuropean
 
Steve, two things come to mind:

1. warped /bent pulley. You can take an 18" steel ruler and lay it across the outside face of the pump pulley and alternator pulley. Turn the pulley and see if the ruler remains parallel to the crank pulley.

2. are all the mounting surfaces between the backside of the pulleys and the balancer and pump flange free of rust or paint buildup?

good luck,
 
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