Alternator bearings? Crankshaft pulley?

2003 base. 127k. Groaning sound upon startup. Lasts a little while then quiets down. Sound coming from the alternator area, but too hard to tell if it might be the crankshaft pulley. Lights seem to dim a bit just as the noise is happening. Very slight movement at the crankshaft belt, but wouldn’t that be common at 127k? I don’t have tools. How will a mechanic go about determining? Listening to it at cold startup? I’d hate to wait too long if it’s the crankshaft pulley needing replacement. I don’t off-road, but the original owner lived in a desert area (sand?) and put 59k in just three years before I bought it in 2006. Probably highway miles. I could just replace the alternator as it’s nearing its end life, but would hate to have it continue (doh!). Strapped for cash at the moment.

 

Try putting a screwdriver up against the alternator housing (automotive stethoscope would be better), and see if you can feel a grinding sensation in your hand holding the screwdriver. This method is great for identifying difficult to pinpoint noises in an engine bay (just be careful to not drop the screwdriver into a spinning belt).

 

Pull the field connector out of the alternator and see if the noise goes away. It could be groaning because it's working too hard.

Also check the battery. If it's partially discharged every morning the alt will have to play catch up every time you start the truck

 

Would I hear a grinding noise with a stethoscope after the noise has settled down (indicating the alternator bearings are almost shot?). Battery is fine. Would one hear the same if worn out crankshaft bearings and past grinding loudly on cold startup?

 

Hard to say. You may or may not. But I'd rule out all the pulleys and idlers on the front of the engine before even considering it's a crankshaft bearing. The pulleys on the front of the engine get exposed to dust, dirt, etc. and aren't submerged in oil, so they're exponentially more likely to be your culprit.

 

I’ve ruled out the top idler pulley. That’s a rather lightweight pulley. The deep gutteral sound is coming from somewhere lower. I understand that crankshaft pulleys are meant to last the life of the engine, but have been known to go bad.They’re also somewhat catastrophic if they fail completely, this concerns me. Alternators are known to go bad at around 125k, and it’s usually other than bad pulley bearings, tho that can happen too. I can quickly replace the alternator. I’m just trying to avoid crankshaft bearings failing completely, which can be catastrophic.

 

Caslon
Sorry, when u say ‘base’ model
2.4/2.7L?
How many belts are ran by your CS pulley(s)?

 

Totally going with alternator bearing dying.

 

Your A/C isn't on is it?

OP take the opportunity and upgrade the alt (search GM alternator to start the rabbit hole)

 

2.4l. Three belts total. AC off. At 127k, how much longer can I expect the Alt to last? They say 125k on average. Maybe it’s prudent to replace it, regardless, along with the belts and top idler pulley. Belts were most likely changed at 59k when I bought it certified used.

 

A firm
so next question
when u see/say you are noticing a slight wobble......is this to the outer most pulley belt ring or the inner most pulley belt ring?

i just had a similar issue if the outer most pulley slight wobble and fixed it

 

Just to add to the mess. These trucks are getting to the age where the balancer will go bad. The rubber separates from the inner part of the pulley. Generally, this makes a belt squeak-type noise. Easy to identify as it'll happen even after start-up and the crank pulley will wobble. Your noise sounds maybe like a bad fan clutch. The fan clutches generally go to full lockup on startup and after a couple of seconds will slow down. If the noise follows the fan clutch ramping up and down you have your culprit.

 

I’ll see if I can produce a sound file and post it. I appreciate the help.

 

Well I’m asking where that faint wobble noticed was coming from Caslon

 

Here’s my story
Same 2.4 as you

I previously did a major job (T-cover gaskets)
All 3 pulleys had to come off
Well technically, 2 pulleys and one harmonic balancer(the same that is a wearable part like tacoman states)

after job done and 200miles afterwards
Heard faint sound…..rotational
Saw outer most pulley(closest to rad) with slight wobble
THatt, member here, convinced me to buy that crankshaft pulley holder from Amazon to get crankshaft bolt as close to the 270ft lbs torque
To do this, had to unbolt the outer most pulley….which I was surprised that the 4 bolts that secure the otr pulley seemed not that tight
I used tool, tightened CS bolt and 4 pulley bolts
No more faint wobble nor noise

I searched for sound with stethoscope, couldn’t pin point sound…I even bought and returned a tensioner pulley thinking that was the sound

 

Yeah its real important to get that crank bolt torqued right....

If that backs off you risk ruining the crankshaft.....

reason Toyota says that bolt is one time use only.




Just blindly stabbing it with an impact is not the best plan.....

really need that tool to lock that while torquing....

For Lexus Toyota Harmonic Damper Pulley Holding Tool Set Crankshaft Crank Holder | eBay