Alternator bearings - can it be replaced

I have a 77 2.7 911. The alternator works fine, but it seams that the bearing is starting to make a rattling sound . (I think its the bearing because I just replaced the fan belt and before it was not making this noise). Is it possible to have the bearing replaced? That sure would beat buying another alternator. Thanks in Advance.

Yes, the alternator bearings can be replaced with the right tools. A local motor/generator shop should be so equipped, and it should be significantly less to fix that way than a rebuilt unit, too!

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Warren Hall
1973 911S Targa

Absolutely! But, when replacing the bearings, it probably makes sense to have the whole thing refurbished (brushes, etc.).

When my bearing went bad, I took it to a local alternator shop. They replaced the bearings, brushes, resoldered the connections, etc. (i.e. rebuilt it), and somehow cleaned it up so that when I got it back, it looked absolutely brand new. This cost me $95. I think he wanted something like $65 to do just the bearings, so it made sense to have it all redone.

Look up "alternators" in the Yellow Pages, you should find quite a few shops. It amazed me that there were so many! I guess its a pretty big business.

HOWEVER, the bearings are pretty strong on these things. If the rattling only started after you replaced the fanbelt, I suspect it really is not the bearing, but instead has something to do with the way you put the new fan belt on. It can be kinda tricky getting the fan belt on using just the right amount of spacers (inside and outside) and making sure that the spacers are on straight and correct.

Brian

Thanks a million for the info guys. Brian, I tried putting on the belt with no spacers just to see if the spacers were the problem and it still is making the noise. I drove the car to work today and noticed that when I turned off my headlights on the car the sound of the noise got lower (as if it was taking the load off the bearing?) does this make sense. I have a 325is and and a 67 healey sprite and usually do most of the work myself, comparably just changing a belt on the porsche seems like a lot of drama!

It sounds like you have the belt on far TOO TIGHT, since I have NEVER seen a 911 or VW beetle that needed to have the pulley on a belt with zero spacers underneath.

The belt should have at least 3/8" to 1/2" 'give' midway between pulleys when at the proper tension. Any less is definitely too tight.

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Warren Hall
1973 911S Targa

[This message has been edited by Early_S_Man (edited 02-04-2000).]

You CANNOT be running the car with no spacers, if you are, you have done something very wrong. I don't think that the nut can tighten down all the way if none of the spacers are there (the bolt part that sticks out of the alternator is not threaded down far enough). That's why it important to always use the correct number of spacers (7, I think?), with adjustments being done by moving these spacers from the inside to the outside of the pulleys.

For example, if your car needed 2 spacers on the inner part of the pulley to get the right belt tension, you MUST put the other 5 spacers on the outside of the pulley. You can't just use the 2 on the inner and toss the extra 5 in the glovebox. You will not be able to tighten the nut down if you do this (and a lot of people do this!). You'll run into all sorts of problems, including wearing a groove into the mounting piece on the fan (look at fans at the swapmeet, you'll see lots with this groove).

I've done just about all the work on my Porsches for many years now, including some pretty involved projects, but replacing the belt is something that I still really don't enjoy. I think there are some intricacies and pitfalls that most people are not fully aware of, and making mistakes can lead to overheating, noises, injured bearings, and scored fans!

Brian

I hadn't really thought of leaving spacers out or off the spacers, pulley, spacers, convex 'washer', nut combination package, but if that has been done, it is probably the source of the noise that is suspected to be alternator bearing noise, as the belt is probably being continuously being 'squeezed' !!! And, Brian is right, there are supposed to be a minimum of at least five or six spacers (in case one or two get lost over the years) with the combined thickness of the pulley and convex washer, before you put the nut on the alternator shaft, or you will run out of threads. One thing more, assuming you get a 'nominal mix' of spacers under and over the pulley half, then find the proper 'give' in the belt, and no noise from belt or alternator or fan hub ... you will need to check the belt 'give' or play in a couple of days, or maybe a week later to see if the belt has stretched any. If it has, you will then need to move a spacer or two to the outside of the pulley, and recheck belt play again. As Brian said, not exactly a pleasant procedure, but one that is necessary to insure long belt and alternator bearing life!

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Warren Hall
1973 911S Targa

Actually, if you left all of the spacers off, the belt would probably actually be too LOOSE! This is because the alternator shaft is not threaded down far enough, as we have discussed. So, the nut and convex washer reach the end of the treads, and can't go down any further, but because of the lack of spacers, the belt and pulley are still too loose, even though you have tightened the nut nice and tight!

I know for a fact this would be the case on my car (I experimented with it once), a '78 SC, but suspect it would be the same for most years.

With no spacers, you would definately get a rattle, but the rattle is most likely caused by the nut/convex "washer" and pulley assembly being too loose and flopping around!

Brian

[This message has been edited by Brian Kumamoto (edited 02-04-2000).]

With regard to your alternator noise, is it becomes a little more quite when you turn your lights off, in all probability you have bad bearings. If the brushes were worn it would continously make noise.

With regard to the belt, depending what belt you have on will determine how it is adjusted. I have mine adjusted without any shims. Initally, when I purchased the car, the belt was tight and had two shims between the pulley. As time went on, the belt stretched and I had to make adjustments.

The correct way to check tension is not to have it banjo tight. There needs to be some flex in the belt.

If you want to be precise about adjusting it, I am sure there is information out there somewhere that will will tell you how much flex it needs to have. However, I have found that when you tighten a pulley so that it has about 1/4 to 1/2 flex, you shouldn't have any problems. Usually after I adjust it, I will start the engine and take a look at the belt to see if it has a lot of vibration to it on one side. If it does, I will adjust it a little more - that is not to say that there should be a little vibration on one side of the belt because it is pulling.

Regards


Steve

I can attest to Brian and Early_man's comments regarding spacers. Running with them out is a big no-no. I made the rookie mistake of changing my fan belt and leaving the spacers out. In-Fact the outside pulley half will not tighten fully. It will rattle, and most likely kick the belt off soon. The worst part is that the outside 1/2 will wallow around on the profiled shaft. This wears a groove in the shaft and means you have to have the fan re-welded, or replaced. I managed to have mine re-welded at StuttgartHouse here in NC, but it still cost me close to $100. I will NEVER make that mistake again.

I don't disagree that spacers are needed to properly adjust the belt tension. But, if a belt is loose and another spacer can be removed to increase the tension then I don't see that it could be a problem. One thing that should be done after the belt is installed and the outside collar and nuttightned, is the engine should be rotated and the nut checked again This ensures that the nut is tight against the base and not against the belt. If the nut it is tight against the belt, the pulley is not fetched up all the way and the nut will eventually loosen.

Anyway, as long as there is slack in the belt after it has been tightened, then it won't prematurily degrade the bearing on the alternator regardless of how many spacers have been removed or installed.

Regards

Steve

Steve, I think you are missing an important point! There is supposed to be a 'stack' of constant thickness under the alternator nut, consisting of a special convex washer, 0-7 spacers, pulley outer half, and 0-7 spacers, with the number of spacers, total, remaining the same!!! It is not a matter of removing a spacer, but rather moving the location of said spacer from between fan hub and outer pulley half to outside the pulley half and under the convex washer. AND, if the total number of spacers in the 'stack' is zero, then the outer pulley half will be cocked, pinching the belt over the top arc, and loose to wobble like a swashplate in the lower arc, resulting in much noise and RAPID destruction of the fan hub, as described above in a previous post, requiring rewelding!!! One final note: if the 'play' or 'give' of the belt exceeds 1/2" with zero spacers under the outer pulley half, with seven spacers under the convex washer and the nut tightened properly, then a new belt is required ASAP, preferably taken immediately from your tool kit, which came with a spare belt and all of the tools to change the belt!

SPECIAL NOTE FOR ROOKIE 911 owners: A 911 driven with a broken fan/alternator belt will DESTROY the engine within five miles!!! Hence, the requirement for a spare belt in the tool kit for ALL trips, and that means a complete tool kit as pictured and detailed in your owners' manual!

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Warren Hall
1973 911S Targa

Scott and Warren are right, Scott makes the same point that I was trying to make in my earlier posts, but Scott does it more succinctly.

You cannot run *properly* without the shims, unless there is something unusual about your specific car (I've never seen one, though). Your best bet is to simply do the right thing and use all 6 or so shims, balanced between the inside and the outside of the outer pulley half as needed to get the right tension. This is how it was designed and this is how it comes from the factory. The shims are $1 each. Just use them!

But, one point has been made for sure: The belt is a lot more tricky than one would expect, and carries many pitfalls for the unwary!

Brian

Brian, You are quite right about the fan belt being a bit more difficult than it looks like at first glance! Luckily, they are quite trouble-free, once installed properly. I guess it would be correct to say that a 911 has a 'fairly' steep 'learning curve' ... including a need for strict attention to tire pressures! I always carry a Draeger pressure gauge with me when going with someone to test a 911. I have seen them, sitting on a dealer's lot with DANGEROUS tire pressures that could be hazardous to drive 'enthusiasticly' without going and correctly filling the tires to spec. I once found a '67 'S' to have: Ft L17 &R33, Rr R40 & L25, which could have led to interesting dent(s) on the driver's side, had I not corrected the pressures before heading to the highway!

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Warren Hall
1973 911S Targa

Ok, maybe I'm missing the point. Let me start over. When I remove a spacer from between the fan hub and the outer, this closes the gap, and the belt becomes tighter. That washer is then palced outside the outer pulley with the other washers and the convex washer is placed over them. If this correct, then this is what I have done. However, I don't have any spacers between the fan hub and the outer pulley and my belt is tight enough not to slip, but loose enough not to load the alternator bearing. Did I do it right or am I wrong?

Regards

Steve

Regards


Steve

Steve,

That sounds like a perfectly 'normal' condition for a belt that has stretched slightly, and you have compensated for the additional length. The only thing you might want to do is listen for any belt 'screeching' or distress when headlamps are on high, heater or A/C on high, and engine idling. And, be sure you have a spare belt and complete tool kit in your trunk at all times! I would change the belt at the first signs of cracking ... on a nice Saturday afternoon!

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Warren Hall
1973 911S Targa

Steve, it sounds like you have done it correctly. You don't necessarily have to have spacers on the inside of the pulley. They just need to be either on the inside OR the outside. Your belt, for whatever reason, is a little longer than a standard, new belt, but if you have all the spacers on the outside of the pulley, and the belt tension is good, you are OK.

If, on the other hand, you took all the spacers out from the outside of the pulley and put them in your toolbox, which some people have done, you would have done something wrong!

Bottom Line: All 6 or so spacers need to be there, it does not matter if they are on the inside or outside of the pulley, as long as they are there and the belt tension is correct.

Brian

Well, I am sure am glad we got that straight. I was beginning to wonder if I had missed something or if something was missing. You are right if you remove the spacers and put them elswhere instead of on the shaft there definitely will be problems. Appreciate your input.

Regards

Steve

BOY! THIS ALL BRINGS BACK MEM0RIES. LEARNED THE HARD WAY THAT ALL THE SPACERS HAVE TO BE THERE SOMEWHERE. DROVE TO A SKI HILL MISSING TWO THAT DROPPED. THE CONSTANT CLANGING ALMOST RUINED THE SHAFT AND PULLEY. CAUGHT IT IN TIME, CUT SOME TEMPORARY SPACERS OUT OF ALUMINUM AND MADE IT HOME.
THE EASIEST CHECK OF TENSION AND WHETHER THE BELT IS EQUALIZED IN THE PULLEY SLOT IS TO TURN THE FAN WITH A SOCKET AND BREAKER BAR PRIOR TO STARTING THE ENGINE. YOU'LL FEEL THE TENSION AND VERIFY THE CENTERING.

Are you sure it is spacers or bearings ??
I had a 79 SC that you could hear a clinking
or rattling noise from the area. For the
longest time I could not figure it out .
Finally it was determined that the outer
pulley disk was damaged and carved a notch
into the shaft of the fan. You could tighten
it down, but shortly after it would be noisy
again. Check this as a possibility.....