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I've done a search but it hasn't turned up much.

I noticed when I first got the engine running again yesterday that the alternator was making a pinking and/or chittering noise. Whilst out today it was even worse and making a rattly knocking/chittering noise.

I'm going to remove the belt and start it up to double check it really is from the fan, but what would people's recommendations be? The alternator was hot to the touch after running, but it's charging fine and the temperature might be a normal thing. The belt seems to be set right with a little deflection and it is possible to force the fan round against the belt with a good amount of force. There's no marks on the shroud so it hasn't been catching.

Cheers.

Just a thought ...

Could it be the chain tensioner isn't operating properly on one side and what you can hear is the chain slapping on the ramps or against the case? Does the sound go away when you up the revs?
I only ask because you say the fan isn't catching the shroud and when the alternator bearing goes it tends to just to make a rumble/rattle.

Mick

It's a possibility. The noise is present throughout the rev range though.

Mine has the oil fed tensioners fitted so I'd think it unlikely, unless it's failed dramatically since the engine was put back together a couple of weeks ago. I'll drop the belt off and and give it a brief test run to check.

If the noise disappears I'll pull the alternator out and have a good looksee.

So it's definitely coming from the fan somewhere. I've swapped the alternator today and it's just as bad if not worse. Leave the belt off and the noise goes away. How many shims are there meant to be in total? I have 5. I'm not convinced it's the cause though. Maybe my fan shroud has become bent, but I can't see that the fan is making contact with it anywhere.

You are always meant to have 6 shims but I doubt that is your problem.

More likely both alternators you've tried have bad bearings. You can get a 911 alternator rebuilt for about £130 at a proper auto electrics place but make sure they have a way to mount it for test or you will also need to supply the fan housing. I can recommend Curds in Tunbridge Wells although that is a long way from you!

Cheers Jonny. While the replacement is a secondhand one it's lovely and smooth, as is my old one now I have it out. I realise the fault may only show once it's loaded up with the tension of the belt, but I'm struggling to believe both have exactly the same symptoms. I've given up for today. I'll take it all back out tomorrow and set it up with my old alternator on my bench to make sure it's all smooth before installing.

I'm wondering if the fan shroud is somehow pulling the two halves of the alternator out of true once they're bolted into the shroud.

Any of your fan blades 'kissing' the housing at all, easy to see any polished points where contact has been made.

Just replaced the alt on my 964 due to a bad bearing and as it turned out worn shaft .... It's noise was very definitely a typical bearing whine as opposed to a chattering.

I can't see any witness marks on the fan housing at all and it doesn't sound like a failed bearing as such. More of a metallic chattering noise as if the fan is making contact, but not in a regular fashion. I'm going to take the whole lot out again tomorrow and build it up on my bench with the fan. I didn't bother putting the fan on until I had the new alternator in and the housing back in the car today as I assumed it would fix it.

http://vid190.photobucket.com/albums/z9 ... ahcs9a.mp4

I've had it all back out again this morning and rebuilt it on my bench with the original alternator. I even mounted the fan while it was out. It spun smooth and free. Fit it back to the car and it sounds as per the video above. Two alternators now, exactly the same. It's got me stumped.

Definitely sounds like something is flexing / moving and then something is catching. Is the housing secure ? Any movement of the fan axially ?

I am sure that sound is the outer pulley half chattering on the hub of the fan either caused by to few shims or the outer domed washer has had the centre depressed by overtightening and so it's outer edge is not putting enough pressure on the outer pulley half. You will also find that the shoulders of the fan hub are being cut into by the movement of the outer pulley around the hub.

Chris

hot66 wrote:Definitely sounds like something is flexing / moving and then something is catching. Is the housing secure ? Any movement of the fan axially ?

The housing is sat on its peg and I daren't do the strap up much tighter. When I try to move the housing the car moves first. The alternator is securely fixed into the housing with all six bolts and all four spars from the outer of the housing to the alternator are solid. Ive had a big allen key in the the shaft of the alternator trying to flex it, but it's solid too.

butzsi wrote:I am sure that sound is the outer pulley half chattering on the hub of the fan either caused by to few shims or the outer domed washer has had the centre depressed by overtightening and so it's outer edge is not putting enough pressure on the outer pulley half. You will also find that the shoulders of the fan hub are being cut into by the movement of the outer pulley around the hub.

Chris

Cheers Chris. That makes sense and of the remaining possibilities has got to be the most likely. I have swapped the pulley half for the one that's currently on. My old one had the groove for the airpump. I have tried putting the old one back on but it's still the same. I'm going to order a set of new shims, cup washer etc and hope for the best.

Personally now I second vote with Butzsi. The outer flange runs eccentric to my eye from that vid so something is not clamped tight?

New shims and cup-washer-thingy installed. The battery in my vernier micrometer has gone flat, but the new shims feel thicker and the new cup-thingy is definitely deeper than the old one. I wanted to hear if it had fixed it, however my Dansk muffler is away having some proper internals put into it as it was too loud and droney. I started the car without the muffler for a few seconds and now I can't hear anything. I doubt I will for a few days.

I'll update for definite when I know it's fixed it, but it's looking promising up to now. Cheers for the advice!