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Strange noise tracked down to alternator. What is it?


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Noticed an odd clattering thsi evening in the engine bay. Sounded like a loose bolt or similar, very rhythmic and 'tinkly' and keeping pace with engine revs.

Checked everything, nothing obviously loose. Eventually tracked it down to the alternator area. Have not been able to get into the back of it yet to see if its a loose bolt.

However later on I had the lights on and flicked the high beam and the clatter increased markedly. Switched lights off and clatter diminishes (but persists). Flash high beam and clatter increases and stays loud until lights are dimmed again. Off, on, off, on noise increases/decreases in response to increased load.

Any idea what might cause this? Bearings? Brushes?

Alternator is only 6 months old, proper Lucas jobbie so still under guarantee. But curious as to what might be up with it.

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10 hours ago, vulcan bomber said:

Is the fan catching something? Or has the shaft become lose in the front bearing allowing it to contact the front face of the alternator. 

Checked all that. There's a lot of space around the alternator, nothing near it, and there's no obvious play in the shaft nor evidence of it contacting the front. Sounds like something inside, but the varying clatter according to electrical load (as opposed to engine revs) is suspicious.

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17 minutes ago, Les Henson said:

Take the belt off it and spin it by hand to detect play and/or noise. It's not that easy to fix them nowadays so you may find it's had it.

 

 

Les.

Aye, thats the next plan - I have an old one in the shed so I'll swap it and have a fiddle with this one when its off. Bit of a pain - this is the second one that's failed - first one arrived in a badly bashed box but looked ok however it failed totally whilst driving in a blizzard in the middle of nowhere about a month later .

Thanks chaps.

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1 hour ago, Roverdrive said:

You said you checked shaft, did you check the fan is still firmly attached to the shaft?

Yes. did that too. It all appears intact on the outside, all tight, no play, no touching anything. Might get at it tomorrow or Thursday and check that all the rear connections are tight.

I've an IBS battery monitor connected to two batteries - its showing full charging going on, and a small LED voltage meter reading out in real time shows 14V + when running, and the tacho connected to the W terminal is bang on too so the output seems ok. But it sounds like its filled with loose bolts! I might try and sound record it -  its quite peculiar.

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Here's the sound file I did this morning with sound recorder beside the alternator to make its noise more obvious than the engine. What you'll hear is the basic alternator with a rhythmic click-click-click that comes in every 2.5 seconds. It continues like this to the 10 second mark where the full beam lights are switched on for three seconds, off for three seconds, on for three seconds etc and you can hear the distinct change in the click-click'click as the electrical load is applied with the lights on.

It's just started to rain so I may put off pulling it apart until tomorrow!

160928_02.mp3

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Is the pulley, or any of the other pulleys, made of two pieces of metal spot welded together, rather than being machined from a solid casting?

My brother had an alternator fault, too many years ago for me to recall the exact sound, where an alternator pulley made of welded plates had one spot weld break.

As the area of pulley adjacent to the broken weld came under pressure of the belt the two plates were forced apart. As the area of the break moved away from the belt the two plates moved back together with a click.

Changing the electrical load will obviously increase the pressure of the belt, forcing the plates further apart, and thus generating a loader click as they spring back.

Regards.

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Checked the pulley - seems to be one-piece and no spot welds so don't think its the problem David mentioned above.

Anyway - oddly - got the new alternator swapped for an old one, and to my surprise the old one is now doing the same clickity-clattery-click. To ensure I'm not hearing the PAS pump or anything else close to it making the noise I disconnected the alternator belt and the noise went away. Reconnected it and its back again, and increasing when I put it under load by putting the lights on full.

When I put the new alternator on a few months back I replaced the ring terminal as the old one was broken, but I don't have a proper crimp tool for these beefier terminals so I made the best job I could with other tools, but I'm wondering whether there's a wee bit of sparking going on - all seemed tight when I put it back together a few minutes ago, but maybe its not visible. (I'll try when its dark  and see if anything shows).

I'll take it apart again tomorrow…or Monday..

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1 hour ago, vulcan bomber said:

Could be the belt needing replacement. I've had belts make a sort of slapping sound In the past... Yet they looked fine.

Never thought of that, possible that some weird thing is going on with the belt - will dig out the emergency spare and try it. Good idea chaps!

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You didn't mention what engine you have, but I once looked at a friends 300tdi, which had a 'tinkly sounding alternator'.
It turned out to be the water pump impeller trying to cut it's way out of the front of the housing.
(Turning the electrical load on and off changes the belt tension, so it doesn't prove that the alternator is faulty, only that it's still producing electricity.)

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52 minutes ago, TSD said:

You didn't mention what engine you have, but I once looked at a friends 300tdi, which had a 'tinkly sounding alternator'.
It turned out to be the water pump impeller trying to cut it's way out of the front of the housing.
(Turning the electrical load on and off changes the belt tension, so it doesn't prove that the alternator is faulty, only that it's still producing electricity.)

Its a 200tdi. Water pump was changed last Christmas, along with timing belt. (of course that's no guarantee its not kaput now of course!)

Well I've tried:

Alternator 1 - engine running, lights off - makes the noise

Alternator 1 - engine running, lights on - makes more noise coincidental with applying load, which reduces when load switched off.

Swapped to another alternator:

Alternator 2 - engine running, lights off - makes the noise

Alternator 2 - engine running, lights on - makes more noise coincidental with applying load, which reduces when load switched off.

Alternator belt disconnected, no noise. Lights on, no noise. Engine revved, no noise.

Belt reconnected - noise, increasing under electrical load.

I've had my multimeter on both alternators and they're chucking out a healthy 14.2V with no load, and 13.9V under load.

 

 

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On 1 October 2016 at 6:09 PM, vulcan bomber said:

Could be the belt needing replacement. I've had belts make a sort of slapping sound In the past... Yet they looked fine.

Vulcan bomber wins star prize!

Took off the belt completely and had a good look - seems it was delaminating but the problem was not at all visible unless the belt was turned inside-out. When it was on the pulley it seemed fine!

Really weird noise for a belt fracture though! Simple fix! 

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