Fan/Fan Housing Noise

1983 911SC 61,000 miles, original altenator
The noise sounds like a bad water pump on a regular car. The altenator tests OK. Could it be the bearings are going out? Im going to replace the fan belt and adjust the tension first. But I don't think that will do it. Anyone run in this?

Hi Doug. Sounds to me like the alternator bearing is going bad.

In my limited experience with the 911 alternator, it seems like it has a clock in it to go out at 60,000 miles. I checked my service records, and my bearing went bad at right around 60,000. I now have 115,000, and I can hear it starting to knock. To test it, I took the belt off and started the car for a brief few seconds. No knock. Put the belt back on, and the knock was there. It is very, very slight (my mechanic at my smog check said I was imagining it!), but it is definately there.

My friend's 81 SC alternator also started knocking at about 60,000.

You might want to check it by taking the belt off and seeing if the noise goes away (only run it for a few seconds, you will very quickly overheat!).

I have also tried finding replacement bearings, thinking that maybe I can take it apart and just replace the bearings, but I have not had much luck. Does anyone know if this is possible? Seem a shame to toss a functioning alternator when it just needs a bearing.