Loose fan belt

[targasc1980]

I'm trying to do a valve adjustment, and as I turned the belt pulley the belt just slipped instead of turning with it, so I couldn't get the distributor rotor to turn. I figured if I increased the tension it might not slip. So I removed the lock nut (which was cranked on there really tight) and removed some shims, and it made the belt very loose, contrary to what the service manual led me to believe what happen. Now I can't get it to tension up back to what it was before no matter what combination of shims I put on there. The belt is loose, and I'm stuck. The belt is old, so a replacement might be necessary but I just don't understand why it's so loose all of the sudden.

[Joe Bob]

How many total shims do you have? Did you have any on the outside AND inside? How worn is the belt?

Belts are cheap, replace it and make sure you have the correct amount of shims and follow the BENTLEY manual. If it's a Hayne's give it the salt water float test.

[Mark Salvetti]

When you removed the shims from under the pulley, did you place them on the outside before retightening the nut? You always need a total of 6 or the pulley half will be loose. Maybe when you went to reinstall, you didn't get the stacks correct?

Next time the way to solve the problem you had with the belt slipping, use your fingers to pinch the belt tighter while you rotate the alternator pulley. That extra tension usually is enough to rotate the crankshaft.

Mark

[targasc1980]

I have six total shims. I believe they were all on the inside before. I tried putting them all back on the inside (and yes I referenced the Bentley manual) and it's still not the same as it was before.

[75 911s]

Dome washer on correct? Dome faces the front.

[tkmoore]

With all the shims on the outside, wondering if the dome washer isn't seated in the notches on the pulley shaft all the way as needed, therefore outside pulley half isn't compressing toward the inner pulley like its dedigned to do? Tim

[Joe Bob]

Try putting two on the outside and do the pinch test.

[Lyle O]

This...I've done the exact same thing, so I know it is possible. Be very careful when you put the dome and nut on that the washers are properly centered under the dome, otherwise it will get hung up. You will know if you see that some washers are no longer flat.

Originally Posted by tkmoore

With all the shims on the outside, wondering if the dome washer isn't seated in the notches on the pulley shaft all the way as needed, therefore outside pulley half isn't compressing toward the inner pulley like its dedigned to do? Tim

[targasc1980]

Originally Posted by 75 911s

Dome washer on correct? Dome faces the front.

Dome washer faces the front? It seems to me like the rounded part of the dome should be closer to the rear of the car. Otherwise the dome washer doesn't make contact with the outer pulley half...

[Mark Salvetti]

I think in this case "front" means the front of the alternator facing you, not the front of the car. The dome should be facing the nut. The spare shims actually are supposed to go under the dome. Here is the Pelican article with photos:
Pelican Technical Article: 911 Fan Belt and Pulley Replacement

The number of shims you need under the pulley is going to depend on the belt dimensions. They are all over the map these days. The original Porsche belts were 9.5 mm wide. The new belts, even though they may be stamped 9.5mm, are actually 10mm or more. See this thread: Can't get fan belt tight enough even with zero shims.

Mark

[puddy]

Small hijack here, I have only 5 shims on my fan pulley, the removal instructions say "make sure you use 6 shims" well I don't have 6 shims and its been fine so far, any reason why 5 won't do?

[tobluforu]

Originally Posted by puddy

Small hijack here, I have only 5 shims on my fan pulley, the removal instructions say "make sure you use 6 shims" well I don't have 6 shims and its been fine so far, any reason why 5 won't do?

No biggie, one was probably lost.

[puddy]

OK thanks, I figured that much and didn't want to spend a fortune to buy 1 cheap little item and pay crazy shipping costs for it. I'll carry of with 5 shims.

[75 911s]

Originally Posted by targasc1980

Dome washer faces the front? It seems to me like the rounded part of the dome should be closer to the rear of the car. Otherwise the dome washer doesn't make contact with the outer pulley half...

Right. My wording was unclear. Maybe another way to put it is the dome covers the outer pulley half (or shims if you have them on the outside) and that the rounded part If yours is rounded -would be toward the rear bumper. FWIW my dome is not a dome at all, but the square type and I know there are a few variations in the washer...



And also I would put the 6th washer in. Now is a good time to buy a filter, gasket kit, and maybe a few other items to up you over the free shipping limit! :-D

[jlex]

The reason for using all 6 washers is that the nut may run out of thread on the alternator shaft giving you a false sense of it's being tight when it's not.

[sugarwood]

Post #16 may be helpful
Would like to try a compression & leakdown test at home.

[jason2guy]

Originally Posted by 75 911s

Right. My wording was unclear. Maybe another way to put it is the dome covers the outer pulley half (or shims if you have them on the outside) and that the rounded part If yours is rounded -would be toward the rear bumper. FWIW my dome is not a dome at all, but the square type and I know there are a few variations in the washer...



And also I would put the 6th washer in. Now is a good time to buy a filter, gasket kit, and maybe a few other items to up you over the free shipping limit! :-D

thats not the right washer. if that washer is beveled its supposed to go between the fan and the alternator. first that washer goes onto the alt shaft , narrow side towards the alt then the fan goes on