Replacing Harmonic Balancer

[1987 GMC Jimmy]

I don't want to have pegged this issue wrong. I've got a wobbly harmonic balancer pulley. It's a light, fast wobble, which I heard if it's a sloppy wobble, there's a crankshaft problem, but if not, it's the balancer. Don't know how much truth there is to that. I checked the pulley bolts, and they're tight as hell. I just wanted to see what the consensus was before I did this. The motor's got 72,000 miles on it if I'm not mistaken which seems premature for this. I'll be pretty upset if I replace this, and it doesn't clear up.

 

[Honky Kong jr]

With out seeing it I can’t be sure but rubber degrades over time not mileage. Mileage is a unit of measure we use time is the great equalizer.

 

[1987 GMC Jimmy]

The PO put it the motor in there nine years ago. Not that long ago, I guess, but I don't know what else it could be. The alternator belt started wearing out really fast, and it's making some noises.

 

[PrairieDrifter]

Grab the outer ring of the balancer and see if you can get any slight movement. Only the centerbolt holds the balancer on, the three outer bolts just hold the pulley on.

 

[74 Shortbed]

The pulley bolts on to the hub not the outer ring, take the pulley off and check for crud between the pulley and hub, if there's crud clean both and try it, if it still wobbles take it off and put a dial indicator on the hub(not the ring)and rotate the engine by hand, if there's no movement on the indicator the pulley is bent, not uncommon to get a bent pulley.

 

[1987 GMC Jimmy]

I checked this morning to see if the balancer was wobbly or just the pulley. I took a video, but I can't seem to upload it directly. The pulley moves some, there's a "wah-wah-wah" noise coming from the accessory belt drive, and the belts associated with the pulley are really twangy even though they're adjusted properly. The balancer moves, too, just not as much. I know there's a physics explanation that has to do with it being more apparent farther from the axis of rotation if you think of the problem more like a top spinning, but I'm not much in that particular field. I think this problem is in an early stage where I'm only having some added belt stress, some noise, and some minimal vibrations. It didn't do that before so I'm operating under the assumption that the pulley is okay, and the balancer is the issue. It looks very clean up in there, but I could only know 100% with it removed.

 

[Honky Kong jr]

I checked this morning to see if the balancer was wobbly or just the pulley. I took a video, but I can't seem to upload it directly. The pulley moves some, there's a "wah-wah-wah" noise coming from the accessory belt drive, and the belts associated with the pulley are really twangy even though they're adjusted properly. The balancer moves, too, just not as much. I know there's a physics explanation that has to do with it being more apparent farther from the axis of rotation if you think of the problem more like a top spinning, but I'm not much in that particular field. I think this problem is in an early stage where I'm only having some added belt stress, some noise, and some minimal vibrations. It didn't do that before so I'm operating under the assumption that the pulley is okay, and the balancer is the issue. It looks very clean up in there, but I could only know 100% with it removed.

Pull the pulley and see if it’s cracked.

 

[74 Shortbed]

It didn't do that before so I'm operating under the assumption that the pulley is okay, and the balancer is the issue. It looks very clean up in there, but I could only know 100% with it removed.

It's impossible to see between the pulley and the balancer, and cast iron balancers don't just bend, very easy to find out though.

 

[1987 GMC Jimmy]

You're right, I could only see around the edge. Well, here goes on that one. Thanks, guys. Just wanted some group consensus before I did a PITA job on my daily.

 

[shiftpro]

Jesse when my money order arrives you can go buy a new harmonic balancer

 

[peats]

i'm in agreement with honky kong, either a cracked pulley or a balancer going south. don't wait to fix the problem because if either one lets go you could be replacing the radiator as well. cant believe you are not throwing belts.

 

[peats]

one more thing to look for, the pulley is pressed with a flange that fits into the balancer opening, if PO hammered on the balancer, the pulley might not sit flat on the balancer. i know because PO of my '65 C2 did exactly that, it would throw a belt at around 5,000 rpm. it finally snapped the water pump and i found the problem when i was installing the new crank pulley. really couldn;t see a wobble before it failed. also if you pull the balancer, use a balancer install tool to reinstall it. i had to replace a crankshaft on my 360 (.60 over) due to the threads being stripped out , again from a PO"s negligence.

 

[chengny]

I checked this morning to see if the balancer was wobbly or just the pulley. I took a video, but I can't seem to upload it directly. The pulley moves some, there's a "wah-wah-wah" noise coming from the accessory belt drive, and the belts associated with the pulley are really twangy even though they're adjusted properly. The balancer moves, too, just not as much. I know there's a physics explanation that has to do with it being more apparent farther from the axis of rotation if you think of the problem more like a top spinning, but I'm not much in that particular field. I think this problem is in an early stage where I'm only having some added belt stress, some noise, and some minimal vibrations. It didn't do that before so I'm operating under the assumption that the pulley is okay, and the balancer is the issue. It looks very clean up in there, but I could only know 100% with it removed.

An SBC developing a crack in the crank pulley - where it is bolted to the balancer hub - is hardly a rare occurrence. Here is a stock image:

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Cracks can also form in the grooves of the belt drive section. Here is an example (this one was found in the pulley of an engine I was rebuilding):

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Either type will cause vibration/runout of the pulley - as well as abnormal performance and reduced life of the associated belts. But, while a cracked pulley is certainly serious (and should be dealt with ASAP), it isn't nearly as critical as losing the "interference fit" of the balancer hub to the crank snout.

An interference fit means that after the two parts are assembled, they essentially become one component - with zero clearance or relative motion. In theory, the crank bolt is only required for assembly purposes and the key is only for timing mark alignment. Point is, there should never be any observable play between the balancer hub and crank snout. So it's kind of alarming when you state:

The balancer moves, too, just not as much.

Like Mason says, the sheave is only fastened to the balancer in the area of the hub:

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So, if you are able to create motion - in the outer ring of the balancer - when applying force to the pulley... it becomes a serious issue. If allowed to continue, it's possible that the crank snout could be damaged - and trust me, you don't want to deal with that.

 

[1987 GMC Jimmy]

i'm in agreement with honky kong, either a cracked pulley or a balancer going south. don't wait to fix the problem because if either one lets go you could be replacing the radiator as well. cant believe you are not throwing belts.

I sure hope so. I already started tearing into it today, but the weather and a PS bolt with a wrench that wasn't long enough got to me. It seems to have accelerated the wear on the alternator micro serp belt, but the other two belts seem to be less affected. I think I caught the issue early and hopefully it's not too bad of one.

 

[1987 GMC Jimmy]

An SBC developing a crack in the crank pulley - where it is bolted to the balancer hub - is hardly a rare occurrence. Here is a stock image:

You must be registered for see images attach

Cracks can also form in the grooves of the belt drive section. Here is an example (this one was found in the pulley of an engine I was rebuilding):

You must be registered for see images attach

You must be registered for see images attach

Either type will cause vibration/runout of the pulley - as well as abnormal performance and reduced life of the associated belts. But, while a cracked pulley is certainly serious (and should be dealt with ASAP), it isn't nearly as critical as losing the "interference fit" of the balancer hub to the crank snout.

An interference fit means that after the two parts are assembled, they essentially become one component - with zero clearance or relative motion. In theory, the crank bolt is only required for assembly purposes and the key is only for timing mark alignment. Point is, there should never be any observable play between the balancer hub and crank snout. So it's kind of alarming when you state:

The balancer moves, too, just not as much.

Like Mason says, the sheave is only fastened to the balancer in the area of the hub:

You must be registered for see images attach

So, if you are able to create motion - in the outer ring of the balancer - when applying force to the pulley... it becomes a serious issue. If allowed to continue, it's possible that the crank snout could be damaged - and trust me, you don't want to deal with that.

I think I got it figured out. I got the pulley off, and it was in good shape. Just a little grease on there and no cracks at all. What looks wrong to me is that the rubber dampener is starting to bulge out from the middle of the balancer at that seam that's on top. It's all the way tucked in at the opposite side of the seam, but it's sticking out quite a bit right there where they meet. The new balancer has the rubber flush all the way around. I took some pictures. Hopefully they show what I'm talking about. I haven't pulled the balancer so I can't speak to the crank snout, but I figured I'd give an update. Good thing I took all this apart, too. I put in a cooling system leak dye and was able to see now that my radiator has two leaks, my lower rad hose was bad, and my water pump looks like it's leaking at a glance.

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