What causes a crank shaft pulley to wobble?

Discussion in 'GM Powertrain' started by Gsquared, Mar 8, 2009.

  1. Gsquared

    Gsquared New Member

    I bought a 2006 Suburban with 75k miles on it about 2 weeks ago and just had the power steering pump replaced and steering shaft too. The day I turned the vehicle in to get the PS pump replaced, I noticed a squealing noise coming from the engine (sounds like a cricket). After getting the truck back, the noise had seemed to go away but now, it's loud as heck. It seems to be coming from one of the pulleys but I can't make out which one.

    Anyway on top of that, today my father-in-law noticed the crank shaft pulley wobbling and he said only one thing can do that, an accident to the front end. Is he right? What else would cause it to wobble and could a bent shaft be the only thing making it do that? I can't tell if the squeaking noise is coming from that pulley but it's sound like it's in that vicinity. He has a 2001 Tahoe with the same 5.3L v8 and we started it up and his pulley is rock solid. So what does this mean?

    I just read from other forums on a Google search that it could be that the pulley wasn't torqued right. Would they have messed with that pulley while doing power steering pump exchange? They did say they did do a full tune-up when they prep'd the truck for resale and maybe they changed the belt. Could something have happened then and am I doing damage by driving it?

    I noticed when making the video that when my wife stepped on the gas (2k rpms), the wobble seemed to go away (I think).

    Here are two clips of the wobble. Don't pay attention to the audio going in and out. My camera records ambient sounds in a weird way.

    Video Clip 1:
    http://s474.photobucket.com/albums/...neral Photos/?action=view&current=Pulley1.flv

    Video Clip 2:
    http://s474.photobucket.com/albums/...neral Photos/?action=view&current=Pulley2.flv
    Last edited: Mar 8, 2009
  2. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    The pulley is pressed on to the hub between a thick rubber dampener. Once it gets bent it's going to wobble. It may have been in an accident or maybe some debris got caught in there. I would remove and inspect the pulley.
  3. Gsquared

    Gsquared New Member

    Man, I'm all for vehicles coming equipped with black boxes so new owners can find out the truth before they buy. The Carfax checked out clean but that's only for damage reported.:grrrrrr:

    Any other insight?
    Last edited: Mar 8, 2009
  4. Z71_guy

    Z71_guy Epic Member 5+ Years 1000 Posts

    If i remember right the harmonic balancer is part of the crank pulley and that part of the pulley may have gone bad.
  5. John W

    John W Rockstar 100 Posts

    Better get it checked as soon as possible because if the harmonic balancer is bad it can break the crankshaft.
  6. KirkW

    KirkW Rockstar

    Any accident severe enough to contact and damage the crankshaft pulley would leave obvious, tell-tale marks in other places. In other words, think of everything else that would have to be crunched before reaching the pulley.

    I'd sooner believe the harmonic balancer is defective, possibly the result of bad service, possibly just "one of those things".

    Just to be sure we're looking at the same thing in the video - the pulley that is centered in the frame of the video is a tensioner pulley. You can see it moving back and forth as it constantly maintains an even tension.

    The pulley in the upper-right of the video frame is the crankshaft pulley. It's hard for me to tell from video, but if that's the one that is wobbling as it rotates, then it most likely is due to a distorted harmonic balancer.

    Replacing the balancer requires a "harmonic balancer puller/installer", one that threads into the balancer mass. You can't use a regular pulley-puller that grips the edges since this will rip the rubber portion apart.

    It's also possibly that the fan-belt pulleys (which bolt to the balancer) are distorted, mis-mounted or bent. It's easy enough to remove those pulleys with standard tools, then check them for flatness and runout on a flat table-top. Perhaps when they were installed (or re-installed following service), some dirt was trapped under the pulley and/or they were torqued improperly, causing the wobble.

    With the fan-belt pulley removed you'll be able to examine the harmonic balancer more closely for damage. Removing the plugs and turning the engine over with the starter will allow you to see if the balancer is wobbling.

    You might get lucky and find that 'two wrongs make a right' - in other words, removing the fan-belt pulley and reinstalling it rotated 180° from where it was makes everything straight again.
  7. Gsquared

    Gsquared New Member

    Kirk, thanks for the information on what a decent front end collision would do to the rest of the engine. I don't see any other issues with the front end of it (not that I would know what to look for) so maybe the problem lies with another faulty part like you mentioned. My father in law was pointing to the tensioner as the crankshaft pulley and he said it shouldn't wobble so it looks like he's got that part wrong. But, regardless, we started his Tahoe up and the "now tensioner":wink: was solid as a rock. Should mine?

    Chevy showed me a service order that showed the truck got an $800 tune up before it was put on the lot for sale so could it possibly be that a new belt would cause the tensioner to "wobble" until it got broken in like his probably is? It's got a major belt squeal too that keeps getting louder and louder so could that help justify the wobble or is the tensioner always going to do that as the belt wears in and out? I just handed into Chevy this morning so I'll tell you what they report.
  8. KirkW

    KirkW Rockstar

    Ok, if we're talking about the tensioner pulley jumping up and down - that could be caused by something as simple as a piece of dirt jammed in grooves of one of the pulleys. If all the other pulleys are not wobbling, then remove the belt and examine it for signs of damage (both grooved and smooth sides of the belt). Some cracking is normal, even a few grooved ribs missing. But if you have several inches of missing ribbing, especially sections of adjacent ribs, then that's a problem.

    While you have the belt off, check all the pulleys to make sure there is no sand, dirt, grease, belt material, etc., jammed in any of the grooves. Check the smooth-sided pulleys for dirt/damage/dents. Try rotating all the pulleys by hand - they should all turn smoothly, with no changes in resistance as they turn. Some will be stiffer than others to turn, but turn they should. The only pulley you can't turn by hand is the crank-pulley itself.

    The tensioner pulley itself might be bad. You would feel bad bearings inside as you turn the pulley - this one should spin easily. Any roughness or looseness indicates a problem. The A/C and alternator pulleys will also spin easily (the alternator has a bit more mass and inertia to its rotation). The water-pump and P/S pump should have a some smooth resistance due to the seals and liquid inside them.

    You said the power-steering pump was replaced. I assume it uses a pressed-on pulley? Make sure it was pressed on all the way so that the p/s pump pulley lines up (is on the same plane) with all the other pulleys. A straight-edge might help, but usually there are things in the way that make using a straight-edge difficult. Try sighting down the belt line to see if its straight.

    Was the belt changed? Make sure you have the correct belt - sometimes you get a belt of the right length, but wrong number of grooves (i.e. - a 5-groove belt mating to a 6-groove pulley - the results usually don't last long).

    This on-line video has a bit of info on what to look for on the serpentine belt pulleys:


    PS - as for the squealing problem - that could be coming from an accessory, or from the belt. To figure out which one, squirt silicone spray on the belts. You can do this while the engine is running, but obviously be very careful of any moving parts. If the silicone spray makes the noise "go away", then the squeal is coming from the belt and all of the above inspections apply. If the noise remains, then one of the accessories is causing the noise. A mechanic's stethoscope will help narrow down which accessory. Or the above inspections of the pulleys will find the offender.
    Last edited: Mar 9, 2009
  9. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    Good Post Kirk!
  10. KirkW

    KirkW Rockstar

    I just found this other link which better explains belt tensioners:


    In particular the following line caught my eye:

    "Excessive movement or rocking of the tensioner pulley, or "belt flutter" when the engine is running. This means the spring inside the tensioner is weak and/or the bushing is worn. The tensioner needs to be replaced."

    In short, the belt-tensioner may simply be worn out and need replacing. It's fairly cheap and easy to do, even for the first-timer.

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