'76 C10 Crank Pulley wobble and squeal EQUALS?

[76C10Stepside]

This has been coming on for a long, long time. For years I thought it was just a squealing belt. Recently, the fan belt "disappeared" while driving it in town. I replaced the water pump and alternator, trying to cure the squealing, no luck. It got a lot worse the first couple of times I ran it, but now it's back to just squealing when I gun it. Needs new spark plugs real bad, so is running a bit rough. I have not driven it at all since replacing the water pump, just ran it in the driveway. It idles fine and is quiet.

I was thinking a galled/spun crankshaft bearing. Then I noticed that the crank pulley was wobbling slightly (never did that before). Found the crankshaft pulley bolts were not tight (the larger center bolt is tight, though).

After tightening the pulley bolts, the pulley and harmonic balancer both still wobble a little, and when I gun it, it squeals for a a second. I tightened up the alternator belt, but it still squeals.

It's NOT just the harmonic balancer that wobbles. Seems to be the crankshaft or the front bearing that is causing the wobble. Edit: Also, NO engine leaks at all, so seals are intact.

So, what's the verdict? Broken crankshaft? Failed or failing bearing? Should I risk driving it around town? My S10 is also down with a mystery electrical short that is probably wires in the steering column, which will take awhile to get to. Need groceries, please help! Happy Holidays!

[GM-power]

I'd pull the pulley and balancer off and inspect it. Put a new balancer and pulley on it more than likey.

[76C10Stepside]

Originally Posted by GM-power

I'd pull the pulley and balancer off and inspect it. Put a new balancer and pulley on it more than likey.

I'll pull them and inspect, but seems very unlikely that they are both damaged (by what?). They both wobble the same/together, and not very much. The pulley bolts were not torqued, but were only slightly loose, not falling off, which leads me to think this would not cause the pulley or HB to get bent. They both look perfect to the naked eye.

One guy told me he's seen crank pulleys wobble and nothing wrong. I still think the crankshaft is cracked or even broken but held together by the engine, or a bearing is bad (probably the front one). I've never had a crankshaft break before, but have read that they can break and still operate.

Will try driving it to the grocery store and see if anything bad happens. At least I have a AAA membership now!

[MountainGoat1966]

I would do the following:

Remove the harmonic balancer/lower pulley.

Set up a dial indicator on the crank (but make sure it doesn't hit the woodruff key or keyway).

Remove the inspection cover on the bellhousing.

Have an assistant turn the engine through slowly with a flywheel turning tool or suitable substitute.

If the problem is in the crank itself, it'll show up on the indicator.

If the crank is running true, replace the balancer and pulley.

Oh, if you don't know already, NEVER hammer a harmonic balancer onto a crank, use a tool to press it on. I made a tool real cheaply using a piece of allthread, a couple flatwashers and nuts. Works perfect.

[GM-power]

Someone could have not installed them properly. And if you have somewhat loose bolts that might be sign. All that old iron isn't like aluminum all that stuff got really tight lol. The balancer soaks in some of the vibration and is hard rubber. If it deteriorates it can cause a wobble. If you had a bearing going down you'd know, a broken crank and uh you ain't going anywhere. I highly suspect a worn or maybe improperly installed balancer.

[76C10Stepside]

Thanks for the advice. Guess it's time to buy a dial caliper.

I rebuilt the top end on this engine 7-8 years ago. At that time, I removed and inspected the harmonic balancer and painted it and the pulleys. As always, I did everything by the book, not really a "hit it with a BFH" kinda guy (much), LOL.
In all the years since, it has NEVER wobbled even a tiny bit, until now. I haven't touched them since. Don't know how the crank pulley bolts got loose. Maybe I didn't use any thread sealant on them.
If the HB is bad, it would be the first time I ever had one go bad in 40 years of car ownership and doing my own maint/repairs. Guess I've been lucky!

Drove the truck to the store this afternoon, and it ran fine. Will put new plugs in it tomorrow and keep driving it near home for awhile and see how it does.

[MountainGoat1966]

In all my years of driving and engine work, I have only seen one balancer slip. It does happen.
And as for the dial indicator, you can get a very good inexpensive one from harbor freight that'll serve you well. It's a tool that may not get used often, but when you need one, nothing else will work.
Good luck, and keep us posted of what you find !!

[76C10Stepside]

Thanks for the tip. I've looked at the ones HF sells and they look pretty good, but was not sure. They sell a lot of junk, but what store doesn't these days?

[MountainGoat1966]

I paid about 25 bucks for the one I got from them, comes with a base and a flexible arm. I am totally happy with it. Money well spent. I used it to set up the front differential in my truck and had no issues doing so. It would measure runout in a crankshaft easily, and you can either use the vise grips mount it comes with or set it up with a magnetic base on the crossmember.

[jetmech85]

I just replaced my harmonic balancer and crank pulley. My pulley was cracked and a bolt broken off in the harmonic balancer causing it to wobble. I used an installer borrowed from Autozone. I ended up keeping it, costing me less than $50. It fits a lot of different engines. If you think your crank is broken then you can try turning the engine backwards. That may cause the break to separate.

[76C10Stepside]

MG: Runout is how far it "pokes out" from where it's supposed to lie, right? Is there a thrust washer on the front end of the crankshaft?

JM: I have pullers. Thanks for the tip on rotating the engine backwards. Not sure I want to know! LOL

[MountainGoat1966]

Runout is how much an object deviates from rotating in a perfect circle. Best I can describe it, anyway ....

[Fhunter1]

I have seen a balancer fail at the elastomer bond between the other ring and inner hub but that just had a horrible rattle.

I would carefully check the balancer as a starting point to be sure the elastomer hasn't failed and allowed the outer ring to move.

Next I would check the run out of the crank nose as suggested above. The video linked below shows how to do it on a shaft , but you get the idea.

https://www.youtube.com/watch?v=s-UG2CZ8VMM

Let us know what you find.