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Old 04-06-2014, 02:39 PM
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Belt Chirps Like a Bird

Its a SBC 327 mounted in a '77 911. The 6-groove belt drives the water pump and alternator from the balancer, with two idlers. See the pic.

The belt makes a chirping noise like a bird. The noise is dependent on rpm, but is not totally uniform. It seems to repeat each revolution of the belt. I have removed the belt and ran the engine, noise disappears. I have spun each of the 4 pulleys that the belt goes over and they all seem good, no grinding or bad feeling bearings. I took the belt off and scraped the edges with a knife to remove the frayed reinforcing strings in the rubber belt. This changed the noise but is did not get better. I reversed the belt, this only changed the chirping pattern again. I swapped the belt with a new one of the same brand (Dayco 5060605), and the noise came back within a day, albeit with a different chirping pattern. I also checked the alignment of the idlers and the pulleys so that the belt is not rubbing on the edges or lips of the idlers. I can make the chirping noise disappear instantly by adding 3 drops of water to the belt surface when its running, but the noise returns in 10 seconds, when the water has dried up.

I will try to attach a video of the noise and me adding the water so you can hear with and without the noise. http://youtu.be/i-bXC3_awzE

Any ideas? It sounds like there is a pack of angry birds chasing me.
Any and all advice appreciated.
Cheers
Mike B
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Last edited by smikeb; 04-06-2014 at 02:53 PM. Reason: Added youtube link
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Old 04-06-2014, 03:00 PM
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Sounds like it isn't tensioned enough...how much deflection can you get using thumb pressure in the middle of the longest open span?? (engine off, of course LOL)
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Old 04-06-2014, 03:22 PM
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Thats usually caused by worn pulleys, they get concaved shaped instead of vee shaped and the chirp is caused when the belt unwedges itself from the pulley. Usually finding the bad pulley and replacing it along with the belt gets rid of it but if its all the pulleys are worn out it can get expensive.

A temp fix is scuffing the pulleys with sandpaper so the polished surface won't squeak as the belt leaves the pulley but it won't last more than a year or a couple of cruise seasons.

I used to clean up worn pulleys on my lathe with a high speed tool with the proper angles ground onto it to refurbish pulleys but its easier to buy new ones.

I don't recommend this but it is possible to sand the pulleys into the proper shape on a running engine using a wooden paint stick and sand paper glued onto it, I dont recommend it...but its been done. I used 60 grit on a stick,but I don't recommend it.

Did I mention that I don't recommend this abrasive stick procedure, you could get hurt and working around rotating pulleys and running engines is dangerous...so I don't recommend it.
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Old 04-06-2014, 03:57 PM
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Thanks Chuck

I just pulled the water pump pulley and spun it on the lathe, then sanded each groove with emery cloth and a sharp screwdriver. Chirping is gone.
If it comes back I know that pulley needs to be replaced.
Cheers
Mike B
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Old 04-06-2014, 04:02 PM
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This sounds just like vbelt issue But it looks like you have a flat style belt If the groves in the
Pulleys are like new I would look into the idler bearings. They may spin over by
Hand ok but at 4000 rpm might chirp like with no grease in them. Just another thought
Good luck in finding your problem.
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Old 04-06-2014, 04:11 PM
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Quote:
Originally Posted by smikeb View Post
Chirping is gone.
Don't you just love it when a good plan comes together?
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Old 04-06-2014, 04:35 PM
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It would not take much mis alignment to cause your noise. I hope it stays fixed and good luck.
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Old 04-06-2014, 09:15 PM
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No Such Luck

So I thought it was gone, but after about 15 minutes of running the noise is back. Pulled the offending pulley off and found it has a GM part number. Its from the air pump off a 1980 Buick Roadmaster, and is out of production. How the hell did this end up on my Porsche?

Anyways, now I need to find a new pulley that will fit this water pump shaft and has about the same offset. I'll start looking.

I may try again with the emory cloth, but a bit more vigorous this time.

Cheers
MB
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Old 04-06-2014, 09:58 PM
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i no help just want to say HI 4JC! good to see your name up there. i WONT try that trick of yours. my f'ing sbc has been chirping for YEARS now as soon as i get over 4000 rpm and i have changed belts pulley, messed with the alignment everything except the paint stick. i will let you know what happens after i DONT try it.
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Old 04-06-2014, 10:20 PM
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Quote:
Originally Posted by smikeb View Post
So I thought it was gone, but after about 15 minutes of running the noise is back. Pulled the offending pulley off and found it has a GM part number. Its from the air pump off a 1980 Buick Roadmaster, and is out of production. How the hell did this end up on my Porsche?

Anyways, now I need to find a new pulley that will fit this water pump shaft and has about the same offset. I'll start looking.


MB
It is likely on your Porsche because it has the correct bolt pattern and is flat enough, meaning no dish or deep offset like stock SBC waterpump pulleys have, to work as a conversion pulley for your engine conversion. There won't be a stock SBC waterpump pulley that is basically flat like that one is.

You never answered the belt tension/deflection question I asked earlier, reason I asked is most folks don't tension multi-rib belts tight enough when there is a manual tensioner involved. It should be tight enough to only deflect 1/4-3/8" at that longer open span section under good strong thumb pressure. Quite a bit tighter than a traditional single V-belt.
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Old 04-06-2014, 10:25 PM
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Tension

I tried pushing on the belt mid span and got about 1/2" of deflection. So tighter is better you say. I'll get out a bigger lever and try again tomorrow.
Does the fact that adding lube/water or sanding the belt solved the problem temporarily discount the tension theory or not? I'm still not understanding what exactly is causing the chirps.

Good-night.
Mike B
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Old 04-06-2014, 10:53 PM
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Water makes it slip more, like on wet roads or ice, so the sound goes away, it chirps when it gets enough traction to drive the pulleys but not enough to prevent slight slippage....same reason a spinning tire howls during a burnout.
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Old 04-07-2014, 07:02 AM
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Is your water pump off to the side? ...you may want to call Renegade Hybrids. They should have a source for the pulley...but If its V belt perhaps just about any 80's GM smog pump pulley can be redrilled for you application.

Does the front of your engine look like this or do you have V belts? Do you have tensioners like the in the pict below? if so they tend to squeak. I diag them by shooting WD40 with the staw in to the center of the idler bearing, the bad one usually quiets down for a minute after a small squirt but sometime there is a washer covering the bearing and prevents the WD from getting in.
http://galleryplus.ebayimg.com/ws/we.../1000x1000.jpg
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Old 04-07-2014, 08:34 AM
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I didnt look at your pic until now, did not realize you were using a flat belt conversion on your Porsche. My little trick really only works on vee belts although flatbelts have similar although smaller vees as well.

Are you sure that water pump bearing isn't on its way out? Once the bearing gets coolant inside the bearing it can chirp or squeal as well. Last water pump I had let go on my 2011 Caravan chirped until it warmed up and a month later it started leaking coolant from the weep hole, it has a flat belt also and it got worse and worse until it started leaking.

P.S. Bull...I dont recommend listening to anything I say!!!

People could get hurt!
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Old 04-08-2014, 12:32 PM
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. Can't recall ever seeing a setup before where the drive pulley contacts the belt twice... maybe that results in an ever so slight difference in belt speeds at the two different contact points because of different belt stretch on each side...? In any event, not much 'belt wrap' around the drive pulley... maybe it's slipping there... although the two idler pulleys on the 'loose' side of each accessory side help with that... maybe moving the idler on the right closer to the drive pulley (like the left one is) would help increase wrap...

. On my '86 Monte Carlo, the serp belt would squeal until the alternator recharged the battery and stopped dragging so hard... or maybe until the slipping belt got warmed up and gripped better...
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