Pelican Technical Article: Fan Belt Replacement Wayne R. Dempsey
Time: 30 min
Tab: $15-$30
Talent:
Tools:
Pulley wrench, 24mm socket (non-deep socket)
Applicable Models:
911 (1965-89) 930 Turbo (1975-89)
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
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.
Check out some other sample projects from the book:
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 dont 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, its 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 dont place the extra shims on the outside of the pulley, the nut will bottom out, and the belt wont 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 wont 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 its 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.
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. Dont 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. 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.
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
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
Check out some other sample projects from the book:
