badabing

on cold startup, very intermittently, i am hearing this clanging noise for 1 - 3 seconds. it sounds like someone is poking a screwdriver in the impeller that is attached to the alternator on on the back of the motor while its spinning. only lasts for a second or two. if you shut the motor down immediately and try again, the noise is not there, you have to wait at least a half hour or longer to get it to make the noise again. any ideas? i will try and record it and post it here.

btw, its a 1996 993 Turbo w/29K miles. only mods are fabspeed airbox and a K&N filter which were installed less than 250 miles ago.

Crimson Nape Racing

hydraulic lifters?

badabing

well, i figured out the noise. the impeller fan is must be wobbling a little and the fins are touching the outer housing. now it does it all the time and it gets worse with higher revs.

how do i fix this?

Robin 993DX

If that's the case, you will have some broken fan blade edges, have you noticed that? the fans are super brittle and will crack on slightest impact.

black ice

Also check with the motor off for scoring on the inside of that housing. I had the same thing when the shaft bearing and/or alternator bearing went. I do remember exactly that clanging noise (my bearing went and a few days later, on decel, you could hear the clanging and see the result on the bottom of the housing). Not a terrible DIY to replace both the alternator and the bearing. Someone smarter than me here might be able to suggest whether it's one or the other from your symptoms (or lack thereof).

Good luck.
Dave

black ice

Oh, and PS - if that's the problem, waste no time fixing it - like Robin said, it will TRASH your blades and housing (cosmetically, at least)

badabing

i looked specifically for some scoring and broken fan blade edges after it happened the first two times, but I didnt see anything. It literally happened for like 1 or 2 seconds each time originally so i guess it didnt really have a chance to cause noticeable damage. after poking around pushing and pulling on the fan to see how much play there was and messing with the alternator belt, i started it up again and it was clanging like crazy. quickly shut her down, pushed things in the opposite direction of what i originally did and it stopped making the noise. that belt also seemed to have less tension and be a bit looser than the others. does that sound like problems with the above referenced bearings?

if so, do i really need a new alternator, those prob aren't cheap and it sucks that it went after only 29K relatively easy miles....

Peter R.

Sounds like a rattling chain to me....no pun intended.
Peter R.

chris walrod

It might not be your alternator bearings, rather the fan hub bearing. Keep that in mind when you are troubleshooting.

badabing

how would i troubleshoot something like this to pinpoint the issue?

chris walrod

After removing the fan and alt belt, you can wiggle the fan and while doing that, watch the alternator shaft. If the alt shaft wobbles, then its the alt bearings. If not, it the fan hub bearing.

badabing

thanks chris. one more question, if its the alternator shaft/bearing, is that something that can be replaced seperately or do i need a whole new alternator?

Amfab

I had an issue with the fan rubbing, and it just barely touched the housing while idling. It would make a sort of "ching, ching, ching" sound. It was so slightly touching that it left no marks and while stopped I could actually slide a scrap of paper between the housing and all the blades. I had to rotate the fan several times to find a spot where one blade was so close to the housing that I had trouble getting the paper in, but it did go in.

I guess that when it was running it expanded just enough to touch the housing and make the noise. The fan is Magnesium and very resonant.

I rotated the fan until I had a little space between it and the housing and took some 220 and sanded it down slightly until it didn't do it anymore. After further really close inspection I found that the blade had a slight crack at its base—with high RPMs and the centrifugal force along with the way magnesium corrodes and the fact that it hadn't done it before I was afraid I'd throw a blade through the deck lid or something—so I ended up replacing the fan, with a used one. So the bearing could have been a little out and that started the whole thing. I am not sure because the fan I bought had a bearing in it and I used that one.

badabing

sounds like the same thing i had, until of course i starting pushing things around in there and then it was clingin and clangin up such a storm that we reactively sheilded our eyes and ran for cover for fear of shrapnel lol