Hey all, I'm losing my mind trying to track down a noise. Keep in mind this is a custom application. We have an 1992 M70 engine, with no power steering pump, non stock alternator, no A/C, and it's converted to dry sump.
We're using the stock water pump pulleys and crankshaft pulleys.

At idle it makes an intermittent chirp like it's a loose belt. I say intermittent meaning if it's not doing it all sounds fine, but when it is, it just sits there at idle going "chirp...chirp...chirp...chirp..." it's both annoying and embarrassing but it goes away as soon as the engine gets over about 1100 rpm.

First I tried a little belt dressing and it seemed better for a few minutes. I tightened the belt and it got louder and more "insistent" sounding. Using a stethoscope didn't help me track down the source. It seemed like no matter where I touch the front of the engine I hear it in the background. I took off the belt that drives the alternator & water pump and started the car, let it warm up, cool down, then repeat and it never made the noise again. To me this showed it couldn't be the dry sump pump, and had to be either the alternator or water pump.

Last night I replaced the alternator and belt and there was no sign of the noise. We drove the car about 3 miles to a cruise night type event and shut it off there, everything seemed fine. When we got ready to leave, we started it to warm it up and after idling for about 3-4 minutes we heard a chirp. It wasn't as insistent as before, but there it was, at idle only. This morning I'm going to double check the belt tension, but if it's loose it should get louder with increased engine speed, not go away I would think. There is no tensioner, the alternator pivots to tighten the belt. Before I go ordering another water pump I thought I'd pick everyone's mind here.

If it's not the waterpump (it's not leaking anyplace) then could it be the damper? We have a mitsubishi that needs a damper replaced after it comes apart every couple years. I haven't pulled the damper out to see how it's made but as far as I can see it almost has to be one of those two. unless it's something internal that just chose not to be noisy when I tested it with no belt.

Suggestions??
thanks in advance!
Chelle

I am thinking "Tensioners"? Replaced that yet?

Hiya Faisal,

doesn't have any.. this is on that custom installation we have.. The belt only goes around the damper, water pump, and alternator. (Dry sump is connected to a hub bolted to the front of the crankshaft). No tensioner anyplace on it. The alternator is mounted where the A/C compressor would normally be. I'm thinking I might want to change that though - make it so the alternator doesn't adjust and make a bracket to use a stock tensioner.
Do you know if the balancer pulleys might be able to tear away if the belt is overtightened? I'm thinking maybe I need to run over to my storage area and pull off a balancer from one of the spare engines to see how it's made. I know on our Mitsubishi the pulleys are part of the outer ring of the balancer and if you over tighten the belts like I did once they will pull the balancer apart pretty quickly.
Chelle

Is the alignment of the alternator near perfect when tightened?

The belt may be running on just an outer edge if the alternator twists when tightening it up. Once you bring the speed up the belt whips/flexes enough to make better contact and quiet down.

Is the alignment of the alternator near perfect when tightened?

The belt may be running on just an outer edge if the alternator twists when tightening it up. Once you bring the speed up the belt whips/flexes enough to make better contact and quiet down.

I'll check that - my best guess at a way to do that would be a straightedge across the face of the pulley then measuring to see if it gets closer or further from the belt as I go toward the end of the straightedge.. I don't have and real advanced way to test the alignment otherwise..
guess I go lay back under the car.. (I don't have a lift either - doing this all in a one car garage)
Chelle

well using a machinist straightedge laid across the face of the alternator pulley it does look like it's very much inline with the waterpump and crank pulley. My guess is it's not pulley alignment causing this. I retightened it just now and am going to try taking it for a quick drive through town and see if the noise is still happening
back in a bit
Chelle