Hi. I hear a 2008 Fit Base with 175K miles and I'm now hearing a metal "shearing" noise that seems to me to be coming from the area of engine where the alternator is or something else connected to the belt that drives the alternator. Unfortunately as the car warms up, the noise subsides but it's very noticeable on a cold morning. As the engine revs up and down and shifts, so does the noise level. It was a warm morning when I brought it to my mechanic and he couldn't reproduce the problem. He says it's an expensive fix to blindly replace the alternator.

Does anybody have thoughts and experiences on whether this problem is more likely the alternator or something else connected to the belt? Is there a way to tell? The alternator sits on top of the engine, the pulley below it is the tensioner pulley, correct? Is there anything else driven by the belt that could be a culprit? The output of the alternator appears to be fine, 14.5V.

If for some reason the problem caused the belt to snap, it won't leave me immediately completely dead (like a snapped timing belt), correct?

Thanks for any thoughts.

 

I'm guessing idler pulley, but it could be any of the bearings in the water pump, AC compressor, or alternator also. It could possibly be the AC clutch, as I've seen several posts about it as well on here. Not sure if that noise changes as the engine warms up though. You can get a mechanics stethoscope for $5 at harbor freight to use to try to pinpoint the location of the noise.

Mechanics Stethoscope

 

Also, driving with a broken belt would not be the best idea for very long, as the water pump won't be circulating coolant, you could overheat the engine and warp a head.

 

Thank you for the quick replies thus far. I looked but couldn't find but any awareness of an online diagram that shows all the devices the belt connects to. Does such a thing exist? Is the idler pulley the one that sits directly below the alternator?

The problem thus far is definitely outside temp related. This morning (15 degrees) very noticeable when car fun for the first 15 min or so but we've had warm weather for NE lately and if temp makes it to the 40s, it's barely noticeable.

The sound reminds me of when my wheel bearing went bad only a slightly higher pitch.

 

I understand but my Subaru timing belt snapped about two miles after going over a large interstate bridge with no break down lane instantly dead in the water. Extremely lucky to be a half mile off the interstate when this happened.

So if the alternator belt snapped, hopefully I could make my way to the side of the road without the car dying.

 

Here is the diagram from the Honda service manual with a few labels I added. The top one is with AC, the bottom is without (and has no idler pulley). Ignore the belt tensioning tool pictured with the part number beside it, it's recommended to use when installing a new belt.

 

Thank you for that chart, very much appreciated! The AC compressor was replaced, I think three springs ago so I hope that is not it.

I borrowed a mechanic's stethoscope from work but I can only easily get at the alternator. The noise is slightly amplified when placing the probe on the alternator but not sure if that is the source or just being carried along from the source. It "almost" seems like the noise might be lower but so hard to tell.

 

You're welcome. You could loosen the tension at the alternator and pull the belt and spin over the idler, AC and water pump by hand to see if you hear or feel any of them grinding. If you're a Amazon prime member, you can get a Gates pulley for $15. I'd replace the belt too if it's old, another $15.

 

a) turn the lights on; if noise increases suspect alternator
b) do same for a/c
c) remove belt on the cold engine (easily said than done); start the engine and listen for the noise. In subzero weather the engine can be run like this for one minute without damage
d) with belt off spin each pulley by hand. First suspect will be belt idler (bearing) second a/c pulley bearing. The warter pump bearings are holding very well( based on Junk yard studies), provided that Honda coolant is used

 

A and B, no, doing either doesn't seem to increase the noise. Will try again in very cold weather. Nor does turning on the AC to engage the compressor.

Unfortunately I'm not really in a position to take the belt off myself.

I did listen to a youtube example of a bad water pump but that sound was more rough and garbled. This is a metallic sound but quite smooth - almost like a knife/ax against a grinding stone.

I hope it's the idler pulley and I hope it will get worse and more easily diagnoseable. I'm assuming it would have to get really bad before the point, the suspect component would actually freeze up.

 

Can you record the sound?

 

Saturday morning is supposed to be cold so I'm going to examine it in more detail then and if this forum will let me, I'll attempt to upload an iphone video. Really though, as I mentioned above, it sounds like a metal grinding noise. Smooth, not choppy., Gets louder and higher pitched as RPMs increase. Can definitely hear it and much louder when placing the stethoscope on the alternator but hard to get at devices below so not sure if alternator is the source or just passing the sound along. Wouldn't it be nice to have a garage with a lift instead of a condo parking lot.

 

I had a similar problem about six months ago hearing a metal bearing type noise in the belt area. Obviously impossible to diagnose with several components running at the same time, plus the engine noise. I simply removed the belt, and spun each component individually. I could hear and feel some roughness in the idler pulley so replaced that and went away. This was around 175k and I drive down some dusty dusty gravel roads daily. There was no play in the bearing and it spun freely - just a slight rough feeling and sound. Likely could have gone many more miles like that but those things bother me and I'm capable of doing it myself.