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Alternator Cooling Fan Bearing Replacement
 
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Pelican Technical Article:

Alternator Cooling Fan Bearing Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$150 to $550

Talent:

****

Tools:

28mm socket, press, puller, bearing puller kit

Applicable Models:

Porsche 993 Carrera (1995-98)
Porsche 993 Carrera 4 (1995-98)
Porsche 993 Carrera 4S (1996-98)
Porsche 993 Carrera S (1998)
Porsche 993 Targa (1996-98)
Porsche 993 Turbo (1996-97)

Parts Required:

Cooling fan bearing or fan

Hot Tip:

Freeze the bearing first

Performance Gain:

Working fan and alternator

Complementary Modification:

Change the belt

Like all classic air cooled 911s the alternator is located behind the cooling fan. On the early cars the alternator and fan ran from the same pulley. As demands for cooling and electrical current increased Porsche went to a two pulley system. This system works great but it meant the introduction of a bearing in the fan housing that allows the alternator to spin at a different speed than the cooling fan. This bearing fails due to age, heat, and use.

If you are hearing a wining sound coming from the cooling fan pulley or the fan is starting to slightly wobble it is time to replace this bearing. There is a fair amount of tension on the pulleys and once the bearing starts to go bad it will fail in short order; worse case: it can cause the fan to contact the fan housing and that will be a mess and very expensive to fix.

The bearing can be replaced by removing the alternator from the fan and pressing it out. The problem is, the fan can be a fragile and expensive piece so you want to make sure you take your time and apply pressure only to the correct areas. If you damage the fan while performing this work, replacement fans are available, but they are expensive. Take your time, follow the instructions here, work carefully and you will be fine. Also make sure to freeze the new bearing overnight to contract it and make installation easier.

Like all air-cooled 911s that came before it, the 993s alternator is located behind the cooling fan and both are powered by belts that connect the crankshaft pulley to the cooling fan and alternator pulleys.
Figure 1

Like all air-cooled 911s that came before it, the 993s alternator is located behind the cooling fan and both are powered by belts that connect the crankshaft pulley to the cooling fan and alternator pulleys. You will need to remove the fan and alternator from the engine, so please see our article on alternator replacement for additional instructions.

With the alternator out separate the fan and alternator from the housing; this should come apart easily with hand pressure.
Figure 2

With the alternator out separate the fan and alternator from the housing; this should come apart easily with hand pressure. Both these parts are fragile and expensive; don't just start hitting things with hammers!

Once you have the fan out of the housing you will need to separate the fan from the alternator.
Figure 3

Once you have the fan out of the housing you will need to separate the fan from the alternator. The alternator shaft sits in the fan bearing and this is a pressure fitting. You will need to use the proper puller and it helps to have three 120mm 6mm X 1mm bolts and thick washers handy.

With the alternator removed you can see the bearing that fails.
Figure 4

With the alternator removed you can see the bearing that fails. This bearing is pressed into the fan and the fan is both expensive and fragile to work with.

The bearing does not sit in the middle of the fan but actually sits in a housing that is pressed into the fan.
Figure 5

The bearing does not sit in the middle of the fan but actually sits in a housing that is pressed into the fan. I have highlighted in a different color the actual outside diameter of the bearing and housing that you will need to press out (red arrow).

The bearing housing also includes the holes for the bolts.
Figure 6

The bearing housing also includes the holes for the bolts. You will need to support the fan around this area to press the bearing and housing out from the fan (red arrow).

Support the fan as close to the bearing as you can.
Figure 7

Support the fan as close to the bearing as you can. I like to find a ring from a wheel bearing puller kit and support the fan in an area before you get to the spokes (red arrow).

With the thick area of the fan supported from underneath place the fan in a press.
Figure 8

With the thick area of the fan supported from underneath place the fan in a press. Never try and press the bearing out with the outside of the fan housing itself sitting on the press or taking any pressure.

Use a 28mm socket and slowly, carefully and evenly press the bearing and bearing housing out from the fan.
Figure 9

Use a 28mm socket and slowly, carefully and evenly press the bearing and bearing housing out from the fan. A 28mm socket will fit is the perfect size (red arrow).

This is what the bearing looks like pressed out.
Figure 10

This is what the bearing looks like pressed out. Carefully inspect your fan for any signs of damage including micro cracks.

It is a very good idea to freeze the new bearing overnight before installing it.
Figure 11

It is a very good idea to freeze the new bearing overnight before installing it. This will help shrink the bearing and facilitate in pressing it in. Installation is the reverse of removal using all of the same care when pressing in the new one. Make sure to install three bolts loosely through the fan and into the bearing to line everything up before you begin pressing it together.

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