'94 Saturn serp belt noise

[billr]

This is the same 1.9L DOHC with A/C and manual trans.  This is going to be a complicated description of observations... bear with me, I need help!  The noise sounds like a very loud belt screech or squeal, and only happens when starting the engine cold.  It doesn't happen every time, and sometimes lasts for just a few seconds, and other times lasts so long I just give up any shut it down and try a re-start.  The noise started happening a year or two ago, and has progressively gotten to be more frequent and of longer duration.  It seems to be alternator-related in that it is more likely to happen if the headlights or heater blower are on when the engine is cranked.  A couple of months ago I put a new serp belt on it and checked all the idlers and driven units for bearing slop or roughness.  The tensioner is a non-adjustable live-spring unit and seems like it has plenty of tension.  Today I pulled the (new) belt off and checked all bearings again, no change.  The belt does not look like it has been skidding, either against idlers on the back-side or in the drive ribs.  The alternator is charging fine, and there are no unusual noises anywhere after the horrible "start-up screech".  I have not checked the alternator output or AC ripple while the noise is happening, but it is now lasting long enough that I may be able to do it; so that will be done soon.  My gut feeling is that it is an alternator bearing, but my experience with ball-bearings is that once they are bad enough for the balls to skid and screech, they never heal again.  The balls or races get all beat-up, or the ball separator/cage parts are destroyed and get wedged between balls and races.  I really don't want to dig that alternator out of there and open it up "on a hunch", but also don't know what else to look at or try.  If I had a really short serp belt I would try driving each item individually with an electric drill or such, but honestly doubt the bad one would screech like that; that would be too easy!  So... give me some ideas.

[Danica]

Are the belt ribs pointy? Should be flat spot at the tip of each rib. Pointy ribs don't grip well.

[billr]

Yeah, the ribs are flat on the top (and bottom of grooves).  The flanks show very little sign of even having been run, certainly not what I would call wear.  The belt looks like new, better than I would have expected after a couple months (maybe even 6!) of use.  Even the white P/N and logo writing on the flat side is pretty crisp and clean, I would have expected that to be more smudged or dirty after running on the idlers.  I just don't think the belt is slipping anywhere.  I think I will start it tomorrow a couple of times with the belt off, make sure it is up in that area and not something like the starter not disengaging!  Oops, I forgot, the other day I tried starting it by rolling down-hill, no starter, and it still screeched; but I will try it without the belt anyway.

[Danica]

Maybe you should double-check the part numbers to be sure your new belt is not one size too long. Parts guy said "This should work."

[NickD]

Did you try hand turning the alternator sheave when cold with the ignition switch on?  Should have a soft start, 10% duty cycle pulse just to let it rev up first before applying full field voltage.  Several aftermarket type regulators seem to omit this feature.  Full fielding an alternator even with any kind of load on the stator is very difficult to hand turn.

Just a shot in the dark.  Another problem when cold with a 10 mil gap between the rotor and the stator, rotor could be rubbing due to worn bearing or a very slightly bent shaft.

[The old man]

Alternator pully nut loose causing pully to slip upon heavy load when starting?

[billr]

I'm pretty certain the belt is correct, but I'll check against an old OEM belt that I still have around.  Interesting note about the alternator field, I'm eager to look into that.  With ignition off it rotates so freely that it seems like there must be no brushes!  I, too, thought about the pulley nut while laying in bed last night.  There is no key there, as I recall, so that is definitely a possibility even though I have rocked it a bit looking for bearing looseness.  And how do I "recall" that there is no key?  Well, as I stare at that beast and consider the R&R job, I think I put in a reman a number of years ago.  If I did, it wasn't a bad job, so likely that thing will come out today for inspection, if nothing else.  And, if it is bad, likely it will go back in today so I can continue to use the car while I get a new alternator from rockauto...

[billr]

It's too soon to claim victory, but I think I found the problem.  I started the engine 5-6 times with the belt off, no screech.  There is a paint line across the alternator shaft and pulley nut, still aligned perfectly and no metal dust in that area that I would expect if the pulley was slipping.  I felt for alternator turning resistance with key on and off and that seemed OK.  I did that mainly out of curiosity, I knew the results would be pretty subjective.  At any rate, no noise from internal rubbing, either way.  The belt length was correct, it matched both physically and by the belt numbers.  Has the suspense built enough yet?  The belt grooves are deeper on the OEM belt!  The two replacement belts were contacting only the pulley OD "tips" with the "root" of the grooves.  There was little-or-no contact with the flanks of belt and pulley ribs.  This difference in depth doesn't look like much, but those ribs aren't very deep to start with.  As much as I love these Saturns, I have to admit that alternator drive is marginal at best.  The pulley is small (about 2.5" OD) and the belt-wrap is only 90 degrees.  I needs all the grip it can get!  Numbers?  Listed below are the groove depths I measured:

OEM  Goodyear "Gatorback" 4050778/5PK1975   .060-.065"
NAPA "Micro-V AT"  25-050778   .045-.050"    Edit: this is a Gates belt
Gates?  778K5/5PK1975   .040-.045"   (no name on this jewel, catalog description was Gates)
Edit:  I now think the "no-name" above was supposed to have been a Goodyear "Freshstart"

I put back on the OEM belt and it is quiet so far, but my recollection is it started squealing occasionally at start-up before; that's why I changed it.  Probably had 150K-175K on it then.

I'm going to contact the supplier about the "no-name" belt, see what they have to say...

[opelgt]

Another thing to try, if the noise starts up again, would be to unplug the ac compressor. The clutch could be starting to seize and cause the screech on start up.

[billr]

No noise yet with the old OEM belt back on there.  Too bad that not even a "fan belt" is a no-brainer to buy anymore.

[billr]

Time to finish this off.  I put on a new OEM-type belt (Goodyear "Gatorback") and there has been no screeching.  It had noticeably deeper grooves than any of the others.

[billr]

And now time to update it!  The screech came back after a month or so, just occasionally at first cold-start.  Although the (live) tensioner seemed to be OK, took good effort to move it away from the belt to change belt, I ordered a new tensioner.  I figured I didn't want to pull the old tensioner out for thorough inspection and then have the car out-of-service for a while if the tensioner was bad; and with two similar Saturns at over 200K, I would use the new one sooner or later.  It turns out the tensioner was bad.  My first clue was that, when the belt was off, it wouldn't spring back (towards belt) enough to allow access to one of its mounting screws.  I pushed it with my hand and it moved (and stayed) in that "full extend" position.  At least I knew I wasn't wasting my time from then on...  I opened up the old tensioner, just one big screw, no crimps, welds, or bent tabs.  The spring was OK, but there is (was) a plastic gizzy-whizzy in there that had broken and was jamming up the works and not allowing full travel.

[rjh1]

question i have is there was no mention of cleaning the pulley grooves out with a wire brush to remove any old belt debris that has a tendancy to collect and spraying with brake clean to make sure the pulleys are clean ?  sorry just my 2 cents

[billr]

The pulley grooves were checked/cleaned when the first belt change was done.