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Pelican Technical Article:

Fan Belt Replacement

Time:

30 min

Tab:

$15 to $30

Talent:

*

Tools:

Pulley wrench, 24mm socket (non-deep socket)

Applicable Models:

Porsche 911 (1965-89)
Porsche 930 Turbo (1976-89)

Parts Required:

Pulley shims, outer pulley half, fan belt

Hot Tip:

Use a exactly six shims when installing the pulley

Performance Gain:

Prevention of fan failure and engine overheat

Complementary Modification:

Replace alternator brushes
101 Projects for Your Porsche 911

This article is one in a series that have been released in conjunction with Wayne's book, 101 Projects for Your Porsche 911. The book contains 240 pages of full color projects detailing everything from performance mods to changing your brake pads. With more than 650+ full-color glossy photos accompanying extensive step-by-step procedures, this book is required reading in any Porsche 911 owner's collection. See The Official Book Website for more details.

One of the most important tasks in maintaining your 911 is the proper replacement and tensioning of the fan belt. If the belt and pulley are not properly attached, it can come loose and stop the cooling action of the fan on the motor. If you don't happen to notice the temperature gauge or the alternator lamp illuminate, then you may overheat and destroy your engine! Needless to say, the fan belt is very important.

Ironically, it's also one of the most misunderstood items on the car, and is often improperly tightened. The system works using a set of shims that regulate the thickness of the virtual pulley created by the pulley half and the fan. As you add more shims in-between the pulley half and the fan, the tension on the fan belt decreases because the pulley width is larger, and the belt rides lower in the valley. In an opposite manner, when the shims are removed from in-between the pulley half and the fan, it pinches the belt tighter. As a result, the belt will ride higher and further towards the outside of the pulley, increasing the tension on the entire belt. The system is similar to the one used on the 356, and has worked well for many, many years.

The key to installing the belt properly is to follow a set procedure that will guarantee the proper seating of the pulley and the proper tensioning of the belt. Start by installing five shims on the inside of the pulley and one on the outside. It is very important to note that the pulley must always have a total of six shims on it, inside and out at all times. If you don't place the extra shims on the outside of the pulley, the nut will bottom out, and the belt won't tighten properly. If you are missing some shims, get some and put them in right away.

Make sure that you tighten the pulley completely. To achieve this, tighten as much as you can, then turn the starter over a bit, and then retighten. This will give the belt a chance to become unpinched from the pulley. You should be able to feel the point at which all the shims are tight against the fan and the outer pulley half: you won't be able to tighten any more no matter how hard you try. The final factory torque specification for this nut is 40 Nm.

The tension of the belt should be tight enough so that the belt can be deflected with your finger about 10-15mm at the half-way point between the two pulleys. If the belt is too tight, move some shims to the inside. If it's too loose, remove some from the inside and move them to the outside. At all times keep the total number of shims inside and out at six.

The fan belt is removed by holding the pulley steady with the pulley wrench, and then loosening the 24mm nut that holds the whole assembly together.
Figure 1

The fan belt is removed by holding the pulley steady with the pulley wrench, and then loosening the 24mm nut that holds the whole assembly together. Don't attempt to remove the pulley without the wrench: doing so can damage the pulley. Take a look in the toolkit that should have come with your car: each one came with a pulley wrench as standard equipment.

The proper order of assembly for the fan hub.
Figure 2

The proper order of assembly for the fan hub. Start with five shims on the inside, one on the outside, and then move additional shims to the outside as needed to obtain the proper tightness.

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Comments and Suggestions:
tom marshall Comments: the bearing of my fan seems worn. But i see no bearing on the parts diagram, what could it be?
September 4, 2016
  Followup from the Pelican Staff: You probably need a new fan. Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Ed R Comments: I had to buy a new pulley and the belt won't go over it. I am not at all happy with how the shims just flop around, I either have the wrong parts or have them installed improperly. Also, take a look at what the crank pulley is doing to the bottom of the fan shroud. What's going on?
July 12, 2016
  Followup from the Pelican Staff: Looks like the shroud is not installed correctly. Possible the alternator was put and put back into the right place. I would start by fixing that issue.- Nick at Pelican Parts  
John Comments: I'm about to order some service parts for my car and wonder what the right size belt for my car is. It's a US 1978 SC 3.0. No air pump or AC pump left if that matters. Thanks!
April 12, 2016
  Followup from the Pelican Staff: I’m not the best with part numbers.

Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Todd Comments: Getting the belts out from under the lower pulley was very difficult for me... Little clearance. Was that an issue for anyone else? Also , my original fan belt was not notched. The new part belt sent to me was. Is there any problem with using a notched belt?
March 26, 2016
  Followup from the Pelican Staff: No problem with the notched belt. I think the design has been changed, also may depend on manufacturer of the belt. - Nick at Pelican Parts  
korybotz Comments: i ordered a alternator belt from here because i could not adjust the belt on the car i bought any tighter. The new belt that showed up is also loose. I have removed all the shims from the fan side? any suggestions?
February 27, 2016
  Followup from the Pelican Staff: Does the old belt fit? If so you have the wrong part number new belt. - Nick at Pelican Parts  
John Comments: An air impact wrench works great for getting the nut off ,no need for the spanner wrench to hold the pulley half. Also make sure you get the right size belt 9.5mm or 10mm x 710mm or it will not work sold here and almost no place else.Napa and Gates have the incorrect size 725mm listed as the proper size which makes finding a belt on road trip that much harder. I have an 85 Carrera and I not sure if or when another size fan belt is needed on other air-cooled 911's.
September 12, 2015
  Followup from the Pelican Staff: Thanks for the tip.

Give our parts specialists a call at 1-888-280-7799. They can figure out what belt you need.
- Nick at Pelican Parts
 
FabioStar Comments: I cut a notch in the handle of the pulley tool, chained the handle around the rear wheel with a long chain, used a long 24 mm wrench, and it came out very easily.
October 18, 2014
  Followup from the Pelican Staff: Thanks for the additional info and feedback. We appreciate it.
- Nick at Pelican Parts
 
Exoticars parts centre Comments: Very helpfull & knowledgable
August 4, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
mag Comments: I believe the 24mm nut was used on cars later than 75? Can you correct me..? My 71 911t has a 22mm nut and your other article states 22mm is the correct size of socket to use.
June 16, 2013
  Followup from the Pelican Staff: I cannot promise I am 100% sure, but I know 964 and 993 use a 24mm nut. It makes sense that they all changed over at some point. - Nick at Pelican Parts  
islandrob/bob Comments: Re: dealing with the 24mm nut for fan belt replacement. I see the end of the shaft has an allen wrench hole. In a pinch if you don’t have the proper pulley wrench can you use an allen wrench to loosen and/or tighten the nut?
May 29, 2013
  Followup from the Pelican Staff: I have done just that in the past. Just be careful. Think about the size difference of the nut and Allen bit. If the nut is over-tight the Allen bit can break. - Nick at Pelican Parts  
dan Comments: Thanks
May 26, 2012
  Followup from the Pelican Staff: No problem. - Nick at Pelican Parts  
Tito Comments: I have replaced all the engine belts because the engine belt light came on. The light is still on, do I need to replace the belt tension sensor. Should I get a new one or can I get a used one. 964/1989 porsche carrera c4 3.6
May 23, 2012
  Followup from the Pelican Staff: Is the switch depressed with the new belts installed? Check the see if it needs to be adjusted before replacing it. Especially if it wasn't on earlier. - Nick at Pelican Parts  
Schnell87 Comments: I faced a significantly stuck fan 24mm nut when I did this project. I found it helpful to place the end of the pulley wrench under the edge of the AC bracket to provide more leverage and then carefully work the nut out with a 24" breaker bar. Be careful not to push too hard or you could damage the AC bracket and or pulley.
February 17, 2012
  Followup from the Pelican Staff: Thanks for the tip. - Nick at Pelican Parts  

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