Snapped fan belt in 1k miles?

[smurfbus]

The pulleys Are not in line so is there Some sort of convex spacer Against the fan to shift the fan pulley a bit backwards? The belt snapped while spinning the tires in first gear

[Ronnie's.930]

Based on the picture, though it might just be an optical illusion, it looks like the pulley halves on the fan are spaced way too far apart. On my car, in order to get the belt the proper tension, I don't have any shims between the pulley halves, but have all of them on the outside, under the concave washer that positions them, and the nut. That way, the pulley halves are as close together as possible, and the belt rides higher in the groove, making it tight enough (about 1/4" deflection). I would have to look it up, but I think there are five shims (maybe 6), and if you don't have all of them in place, the outer pulley half won't fit right.

Let me know if you would like some pictures or more details about what I am talking about.

[flightlead404]

There are 6. On mine 1 shim inside and 5 outside gives me just less than a 1/4 twist in the belt with my fingers.

[smurfbus]

It was tight enough IMO but I could try even tighter. I even had to loosen it a bit so it was not too pinged. IIRC two shims outer at the moment. If I look straight at above the pulleys there is about 5mm or 1/4in delta so the belt has to twist on its rotation. This is a GSF EFI pulley. It looks like the stock AC pulley had the same problem as the fan housing limits how deep the crank pulley can be fit. Thats why I would like to test some spacer on the fan unit.

[Jeff NJ]

I just looked at mine and the pulleys line up perfectly. Are you sure the fan housing assy is mounted properly?

[Ronnie's.930]

So Smurf, you are talking about adding a spacer between the backside of the fan hub and the alternator nose bearing, correct? I'm pretty sure that mine had a fairly thick one (about 4mm or so) there, but I just looked in the PET and they don't show one - regardless, I'm sure mine has a spacer there.

[Ronnie's.930]

I also wanted to mention that the leading edge of my fan blades sit about 12-13 mm into the bore of the fan housing as measured from the flat portion of the outer lip of the housing - your fan "looks" to be much farther in.

[smurfbus]

I did not touch my fan housing when engine was out so if it is too deep it has been like this for some time now. It is possible that i forgot to add a spacer on the back side of my fan hub when it was apart 3 yrs ago?

[smurfbus]

Looks like I'm missing #10 or #15 ? This was some random pic I found from quick search on "Porsche fan hub diagram"

[Ronnie's.930]

^^^ That's a fan and alternator assembly for a 964 - quite a few parts that 1989 and prior do not have.

I'll continue to see if I can find a part number for the spacer that mine has.


Post #8 of the linked thread has a really good picture of the OEM spacer (still haven't found a part #) and other posts (#13 and others) show someone's homemade spacer used for a problem like you are having.

911 alternator spacer question

[Alan L]

I put an aftermarket alternator in mine a few months ago. The pulleys did not line up by over 10mm (1/2" to you guys.) I had to make a spacer and then shims to get it right. The belt was rubbing on the bottom of the fan housing as it tried to line up the fan pulley. It sounds like you have a misalignment issue. If the fan pulley is 'short' you can fix it by putting a spacer in behind the alternator - in the back of the magnesium housing. I made mine out of aluminium plate (10mm) then some shims.
Alan

[smurfbus]

Yep, it sounds like I need to put a spacer back there. I have a valeo alternator and too bad I dod not spot the misalignment when I installed it. Not much miles on it though as it has been under wiring rebuild and top end rebuild for some time now.

One thing that conserns me though is that IIRC the fan pulley was already pretty close the outer flange so there was not much lip left for the thin spacers. Now if I put a spacer on the axle it would come even further back?

I'll check how it is and report back. Thanks gyus

[Alan L]

I can't quite picture it but I think you are saying there was not much thread on the pulley shaft? ie if you put more spacers under the belt you would be tight on thread? I had the same issue and the nut is short of fully on by about 1 turn. It was worse than that initially and I'm trying to remember how I fixed it. Obviously you would take any spare spacers out from behind the nut - where they usually store them.
Alan

[Alan L]

If your alternator is too short for the housing, you should have extra length protruding on the thru bolts holding the alternator to the housing.
I think I had a collar on the pulley shaft too - which I had to trim by a mm or so to get enough thread on the nut. Every mm I took off the collar I had to compensate for in the back of the alternator.
Alan

[smurfbus]

Hmm...I think I had a brain fart. I have room with the threads but the flange that has cut on sides has just little room for the thin spacers but that should move along with the fan hub : )

Copy of the pic Draco had posted on another thread.

[JFairman]

There is a spacer on the alternator shaft behind the fan like Ronnie mentioned. A year ago last July I installed a really nice rebuilt Valeo alternator that puts out 160 amps.
In these pics I took before installing it you can see the spacer/washer on the shaft of the rebuilt 160 amp alternator picture and in the second pic it's laying on the plywood a little above the older 90 amp alternator on the right.
Maybe yours is missing this spacer?

[smurfbus]

I have the same spacer. I managed to add one 2.5mm spacer and now the nut is flush at the end of the axle. Still a bit offset but better.

If this is not holding up the belt I think next one would be to offset the long bolts of the hub to alternator but that's something I'm not too keen to try as it might do more harm than good?

[JFairman]

Something is not right.
There's a dowel pin on the bottom of the fan housing that has to line up correctly for the fan housing to mount in the correct position on the engine case.
If that pin is in place maybe the fan housing or the alternator is not the right one for your motor.. or maybe your crankshaft pulley is the wrong one.

Mine has the original steel pulley for an '87 930 motor with AC and everything lines up perfectly so I don't know what's happening with yours.

good luck with it.

[Alan L]

It looks like the same issue I had. The alternator needs to come forward in the housing by about 10mm.
Alan

[Norm K]

^^^ This. Although I can't look at mine right now, it appears (in your first pic) that your fan is sitting deeper in the housing than it should.

I think this is more normal ...