(See updates. This isn't really about an alternator after all.)

Just replaced the alternator on my 89 4.0 Renix after a mud pit killed it. Other symptoms were a lot of mud to drive out of the radiator, and the pressure washing that drove it out.

Now I have a loud metal-on metal sound on startup. Gets better when the engine heats up, but doesn't go away. Sounds like (though may not be) a rotating assembly somewhere that sounds like it's catching somewhere as it turns. Sort of staccato chirruping. Not really like a belt noise, but checked that first. Loosed the belt again and turned pulleys by hand, none made a noise that way or seemed to turn roughly. No obvious catching on the radiator fans.

The replacement alternator wasn't identical -- same mechanical fit but the plug for whatever lead isn't the mains was in a different spot on the casing.

So before I start at the bottom and work my way up, any ideas?

Update 02/03/2014: I wish I'd called this "Week of the howling bellhousing."

Update 02/01/2014: Took a look behind the inspection cover. Flex plate looks OK but noise is still in full effect. of the howl. And a longer video just for amusement.

 

My first thought was idler pulley/bearings.

I think I read somewhere several years ago that they can be taken apart and serviced on yours, but I am far from certain on that.

 

start with the basics, make sure that it is actually something on the belt drive, remove the belt and run it for a minute, see if the noise goes away.. if it does go over everything again...

 

Very sensible suggestion. Just tried it, didn't help. Couple of the pulleys have a tiny bit of play, nothing to speak of.

Noise is 100% still there, so whatever it is isn't the belt or driven by it. Noise actually sounds like it might be coming from inside the motor. Reluctant to jump to that not just because it sounds terminally expensive, but because it pulls and drives normally enough that it's hard to believe there's catastrophic interior damage in the mill (naive hope, maybe.) Oil level looks fine.

Anyway, not quite sure what to inspect next. Suggestions still welcome

 

Did you drop a nut or something and get it stuck behind the crank damper or something silly like that? The noise wasn't there before the alternator replacement and it is not the alternator if it doesn't go away.

 

Some of us have left the inspection plate off the front of the bell housing. Stuff might get in there.

 

See if the crank pulley aka harmonic balancer, is rubbing the front cover.

 

Absolutely can. Done it a bunch of times.

 

x2 on checking for mud packed in behind the flexplate if it sounds like its inside the motor, if your oil pressure is good, I doubt its internal... also make sure when you were beating on it in the mud that ya didn't crack the flex plate.. or is it a 5 speed? just a couple more things to check...

 

AW4 and NP231.

 

Take the belt completely off and remove from engine area.

Start the engine and see if the sound is still there.

If it's not, you know your problem is somewhere in the front dress.

If it is, it's internal to the engine or tranny. Or around the torque converter/ring gear.

Heck, it might be the *new* alternator and its bearings. You could take it and have it tested where you got it from. I hope not Autozone.

 

Took the inspection cover off and blew some crud out, but need to get in behind the plate properly (haven't yet). Does sound like it might be the source of the noise.

 

OK, took off the inspection cover. To the untrained eye the flex plate looks OK. There was some dried mud in there (not a lot) which I blew out. Put it back on, whatever was grinding is still grinding.

I'm thinking the next step might to drop (or get someone to drop) the transmission for a proper inspection of the flex plate area.

Video of the noise it's making. More education welcome if anyone recognizes this particular howl.

 

Any happy Seahawks fans care to speculate?

 

They're too busy partying.