What does a failing Harmonic Balancer sound like?

[djwarner]

My '71 Series I had an aftermarket AC installed when new, only to have it removed in 2003. A three pulley harmonic balancer was left on at that time.

This last year I installed a VintageAir R134 system, mounting the compressor where the air pump once resided. System worked well but soon developed a growl near idle and at superhighway speed. The growl disappeared when the compressor was cut-out.

Writing to VintageAir, they said a bad compressor would make noises at all speeds and I probably had a harmonic problem due to something being loose or vibrating. Not finding any loose bolts, I did find that the drive belt was wider than the harmonic balancer pulley grove and wider than the fan belt. So I replaced the belt with the same profile as the fan belt.

With the new belt and listening carefully, I realized that the growl was also present when the compressor was off, just louder with the AC on. Using the tach in my timing light, the growl is present from 940-1050 RPM. It also appears at about 2000 RPM, just much quieter.

Just what does a failed harmonic balancer sound like?

[Zed Head]

Could be the AC belt idler pulley bearing. Remove the AC belt and run the engine and see if the noise goes away.

The water pump and alternator belt will still put tension on the damper. You can run without that belt for while also to see if the noise comes from one of those two. Then run with just the AC belt on.

Don't know why someone would suggest a damper problem first. That would be the last place I'd look.

[djwarner]

The compressor mount has no idler pulley, the compressor swings on the lower mount points like an alternator. Alternator is also recent. This leaves the water pump, crank pulley, and compressor.

I like you idea of removing the belts one at a time to isolate the problem, will do. I'll also check for free play on the crank pulley while I'm at it.

[AZ-240z]

My two cents, as an aside. Generally, when tightening belts, I believe people have a

tendancy to over-tighten, putting undue stress on drive shaft bearings and seals

associated with whatever is being driven.

When the recommended slack is, say, 1", I try to err on the loose side. I would

rather re-adjust for any slipage resulting.

Dan

Edited July 26, 2013 by AZ-240z

[djwarner]

Problem resolution: Despite my tightening, loosening, adding nylon washers, the problem never went away. In fact, like many resonance problem it eventually got worse and lower in frequency. I finally realized it was not coming from the compressor but from the front of the engine. Thinking it might be a cracked heat shield, I began reaching around and wiggling things, I found the problem, a failing nipple on the air injection check valve. When someone remove the air pump many years ago, they cut off 3 inches of the rubber hose at the check valve. They inserted a bolt to seal the hose and applied a clamp.

The hose with a bolt on the end acted like a tuning fork tine and eventually induced a crack in the nipple at its base. A slight tug on the hose and the nipple separated. I found a small circle of hardened tar like substance in the opening in front of the diaphragm. The check valve appears to be sealing, and the resonance is gone. I have no idea whether to try to find a replacement valve or leave it like it is.