How to identify which pulley/bearing is going?

[acfortier]

I've had a pulley/bearing going bad for some time now, and the noise it's emitting is definitely getting worse, but I'm having trouble actually identifying which one it is. Even using a scope, I put it behind the idler pulley, but it doesn't seem any worse than the A/C or power steering.

 

Just looking at the belt when the engine is running, I can see the harmonic balancer and water pump have slight front-to-back play in them. I know the harmonic balancer needs to be replaced at some point (timing marks don't line up correctly). I know the harmonic balancer doesn't have a bearing, so seems unlikely it would make any noise at all.

 

I haven't used the A/C since I've had the truck as it needs to be filled. Unsure if that could be the pulley/bearing going bad. Power steering seems fine, as it doesn't make any worse noises if I actually move the wheel back and forth while stationary.

 

Maybe it's the water pump? Hard to scope it while the truck is running.

 

How else do people diagnose without just throwing parts at it? If anything, I'd start with the idler pulley and go from there.

[gogmorgo]

Pull the belt off and give the pulleys a spin on their own. See if they wobble or there’s “grittiness” to the movement. 
 

If the harmonic balancer is having problems it can rub on the timing cover, or push the belt against something. 
Usually if the bearings in the water pump go it’ll start leaking coolant out the weep hole or shaft seal. 
Also worth poking the distributor with your “scope”, although if that’s having issues it’ll likely give you running problems too. 

[acfortier]

1 hour ago, gogmorgo said:

Pull the belt off and give the pulleys a spin on their own. See if they wobble or there’s “grittiness” to the movement. 
 

If the harmonic balancer is having problems it can rub on the timing cover, or push the belt against something. 
Usually if the bearings in the water pump go it’ll start leaking coolant out the weep hole or shaft seal. 
Also worth poking the distributor with your “scope”, although if that’s having issues it’ll likely give you running problems too. 

What's the thought with the distributor? I've had it out a few times recently, trying to stop it from leaking oil (which it still does, sigh). That could be the source of the noise?

[gogmorgo]

Just something else external to the engine that might be making noise. There is a bearing in it. But if the thing is bad enough to make noise the amount of motion in it would make for erratic spark as well.

If the base is leaking bad enough from the mounting gasket the bearing may not be getting good lubrication. If it’s leaking from under the rotor, that’s a strong indication the bearing is worn out. I can’t say I’ve ever had one make much in the way of noise, but I’ve had a couple start puking oil from under the rotor, both times after chasing a stumble for months. 

[Htchevyii]

I had a distributer squeal in my 4.0 once that sounded exactly like a squealing belt. It was very easily identifiable with a stethoscope.... once you figured out to put it there.  It would come and go and somehow always stopped when you had the hood open.

[acfortier]

Huh, I'll have to scope it and check it out.

 

The base is leaking, already replaced the gasket with an o-ring here: 

 

I'm assuming since it's still weeping out, I have excessive crankcase pressure, but it'd be interesting if that could also cause the bearing in the distributor to fail by not getting good lubrication.

 

[cruiser54]

[75sv1]

Harmonic balancers make noise when they are slipping. Put a white line across the hub and the outer ring. See if it stays in position after running it. I change mine on any 'new' old vehicle I buy. They are about $50. Good time to check the timing chain. A lot cheaper than replacing a crankshaft.