B18 Help - Screaming Alternator

[DWeed144]

Hi All.
145 owner here, but with a B18 from an amazon under the bonnet, so I thought i'd post this here!

On installing the engine, I put in a new alternator, a Denso 60A, and switched it over to the right side under the exhaust manifold.

The alternator screams when under load.

It's been unresolved for months now.

I thought I had cooked the bearings, so I bought fancy high temp skf ones, and rebuilt the alternator, but it still makes the same noise. (crucially - i'm not sure if it did for the first 20 minutes or not...)

I've attached a video.
When it's running the lights on full and the heater fan it screams. When they are off it tends not to.
When I unplug the cable activating the alternator it stops.

Does anyone have any ideas?

Obvious things:

I aligned it with a laser level and it seemed dead on

The output under load is around 14.4v

Cheers!

https://youtu.be/MAhpK9ncr1s

[Derek UK]

Sounds like the slip ring needs a clean up and a new brush fitted.

https://www.youtube.com/watch?v=CImyX5KuGvQ

https://www.youtube.com/watch?v=LqvTHJVQU5g

Note comments about noise about half way through the second part.

[Ron Kwas]

DW;

I think you've answered your own question: "The alternator screams when under load. "...especially when you've already replaced the other typical cause (bearings)...and if Alt chirps like that (not to split hairs here but I'd call that an RPM dependent chirp, not a "scream" which would be more of a constant high pitched howl) , I'd say it was caused by Belt slipping due to high load (you did state it is load dependent: "When it's running the lights on full and the heater fan it screams. When they are off it tends not to. When I unplug the cable activating the alternator it stops.
" ...is there a constant heavy elec load on sys?, or is Battery heavily discharged? ...if yes, Charge overnight with a Mains powered Charger or does Bat have a shorted cell which would cause high Alt load? Have Bat Load tested!), OR Belt is on the loose side (tighten, but not overtight, like a violin E string!) OR Belt and/or Pulley are polished and again allowing load dependent slipping (recommend at least breaking the glaze on it, and/or pulley with some 100Grit sandpaper, or replacing Belt). I have no experience with spray-on "Belt-Dressing" but I expect that is a quick solution which may last only from 11 'til noon...

Last idea: Pulley alignment is less than optimal...I realize you've "aligned it with a laser level and it seemed dead on", but you might want to recheck this, if previous suggestions are not fruitful.

Good Hunting!

[DWeed144]

Thanks Derek and Ron.

I hadn't thought to look up a video - I will watch that and find the sections you mentioned.

Also - the belt is a toothed V belt so I'm going to swap that for a smooth one and see if that works better.

Plus - definitely a low battery.

So lots of obvious bits for me to troubleshoot before I come back with any more questions!!

Thanks!!

[Underdrive]

You can easily test the belt to see if that is the source of the noise by spraying it with soapy water the noise should temporarily stop if that's the culprit.

[Derek UK]

I had a nasty chirp on my Amazon. It would often give a squawk when starting up but could be provoked if you gave it a bit of sudden throttle. This was with a dynamo but I was using a toothed belt. Belt was adjusted to the book but grip was obviously lacking. Change to a "solid" belt brought an immediate cure. Not unusually with dynamo end plates having the holes a bit worn the alignment isn't perfect but that shouldn't make too much difference if the misalignment is small. Continuous slipping will glaze the pulley as Ron says so it might benefit from a scuff up with wet and dry.

[DWeed144]

Thanks for all the feedback.
A solid belt rather than the toothed one resulted in immediate silence.
Although then the alternator pulley was hot enough to burn a finger within about 3 minutes of running. I haven't had much time at all so I had to abort my investigations and then with Christmas I haven't had a chance to get back to it.
I'm going to revisit with reduced belt tension (or should I increase it to avoid slippage which would be causing the friction/heat?) and a freshly charged battery tomorrow.

[Derek UK]

Alternator pulley is only likely to get hot if the belt is slipping badly. Tension of the belt should be set up just tight enough not to slip. About 1/2" deflection in the longest run of the belt is listed as correct. With glazed pulleys you might need it a fraction tighter. You should be able to turn the engine with the fan without any slippage but it might just slip a bit when the engine comes round onto compression. This gives you a ball park idea as to when the belt is tight enough. Too tight is bad as it loads the water pump too much and can hasten wear of the bearings. Adjustment should be "just enough" to do the job.
When the alternator is working hard charging a flat battery at the same time as the headlights are on for example, it is harder to turn by the belt due to the increased electrical load, so it must have a certain amount of tightness to take that into account.

[DWeed144]

I've cleaned up the alternator pulley, so that should have got rid of any crud it had picked up from the glazed belt.
I've put in a fully charged battery and re-tensioned the alternator.
Everything is running very smoothly and absolutely no heat build up or chirping.
So fingers crossed that has sorted it!
Thanks everyone.

[Ron Kwas]

DW;

I agree with Derek about Fanbelt tension, but still believe that high load was the root cause...once Bat is fully charged, Load is once again minimal...even after normal Starting (not extended cranking), Alt Load is high for only a limited time (while Starting energy is recharged into Bat), which is typically less than a minute.

Cheers