Alternator bearing question

[4X4V8]

It looks like I will have to drive my 2001 P38 Thor 4.6 a 600km round trip to the sth coast next week for work.

The 150amp Bosch alternator sounds like the bearing(s) is/are on the way out. It seems quiet on cold start up but then as the engine warms it eventually gets noisy, the bearing noise coming and going other times consistant. Without video/audio it is hard to describe, but I know it is coming from the alternator and it is a sound I have heard before from noisy bearings. Not high-pitched, not a low grumble but somewhere in between, and alternating in pitch.

Not probably relevent but Scangauge shows good charging rate of around 13.6-13.8v when engine up to temp. Around 14.2v when cold.

My questions are, how long can an alternator bearing continue when noisy before failure, and what happens when they fail?

I also am not clear why the OE alternator produces 150amps when the only replacements are 100amp, 120amp or 130amp. If the common experience is that this alternator is about to seize anytime soon I wonder if I can get a good used one (130amp?) to take with me.

I realise this is in part a 'how long is a piece of string' question but I do not have any experience of this situation. Any advice gratefully recieved.

[theelms66]

Definitely piece of string . Damage wise seized alt will lead to broken belt which will lead to overheating. Get where I'm going.
Remove belt and spin all pulleys manually and ensure alt is at fault.

[I Love My Landy!]

Are you sure it is not fan belt noise? I've heard the v-belts in my 110 make some TERRIBLE noises (much like a worn bearing). Spray a bit of water on the belt. If the noise changes/disappears then it's just the belt! Does your motor use a serpentine belt? I assume they could make similar noises.

Any alternator issue should be fixed sooner rather than later.

The alternator in my V8 110 (Bosch alternator from an XD falcon) wasn't charging well for a long time. "She'll be right" i kept saying, until it stopped charging completely one Sunday evening, in the pouring rain, with darkness falling, and a long way from my spare regulator at home! Another time i had a noisy bearing like you, so I bought 2 x new bearings (only $6 each). I kept putting off fixing it though, until one day the rear bearing seized then collapsed. This happened far from home again of course! This let the armature/rotor hit the pads on the stator causing shorting in the wires, which meant the stator was basically irreparable. A new Bosch alternator was worth $440 - much more than the cost of the two bearings! (Luckily i had access to alternator parts from a Volvo 240 that fit and fixed the problem).

Edward :)

[4X4V8]

Definitely piece of string . Damage wise seized alt will lead to broken belt which will lead to overheating. Get where I'm going.
Remove belt and spin all pulleys manually and ensure alt is at fault.

Wise words - thank you. I did the long screwdriver 'stethoscope' method on both alternator and serpentine belt tensioner and the noise was louder on the tensioner. I've given up for today but tomorrow will release the tension on the belt and as you say spin the tensioner and alt pulley and see what happens. I need to get myself the fanbelt removal tool but the belt looks okay (not cracked at least) so I don't think I need to remove it entirely to get to the tensioner and/or the alternator.

[4X4V8]

It appears that it's the belt tensioner pulley bearing that's gone, not the alternator. It has a small amount of play in the bearing and when you spin it it is a bit noisy, comes to a stop with a kind-of vibration (I don't know how else to describe it). The alt pulley seems a bit harder to spin (which makes sense) but seems smooth and little if any noise and no play I can feel.

$100 for the tensioner v about $350 for an alt. Got to be happy with that, esp at the moment. The sth coast job is my last work of any kind for the foreseeable future.

theelms66 thanks for reminding me to never assume anything!