Fan Belt Adjustment
An incorrectly adjusted fan belt may shorten the life of the belt or
the generator pulley leading to repairs on the side of the road. Are
you prepared to replace a pulley or fan belt when traveling away from
Last modified: Sun, 30 Jan 2005
||On the way home from getting my car back from the shop after
the engine rebuild the red generator
light lit up. I pulled off at the next opportunity and saw the belt
was fine, so I was still cooling the engine. I
pulled the generator and, again thanks to
near-by AutoLectrics, I had the generator back in a day and shortly
received a new voltage regulator from
Will at CSP.
||A few days later I needed to test my own advice to see if my car could
be repaired by the side of the road, or would I be stranded when the
fan belt destructed with a bang?
Why did this problem occur?
Usually the problem with belts or pulleys occurs because the sheaves
are not installed correctly. This can lead to broken sheaves or belt.
||I had a spare belt in the car.
I also carry in the emergency bag in the trunk new pulley sheaves
and a new hub. The recommendation is to change all three because often
pulley problems are caused by the hub. Back when these things were
important, the guarantee on the pulley sheaves was voided if a new hub
was not installed at the same time as as the pulley halves.
I decided to change pulley halves with the new belt, in part because
we seldom see powder coated pulleys. A friend told a story that they
had experienced multiple belt failures attributed to powder coated
||When I got home, the pulley was running hot and the belt tension was
loose. Hmmm. It was tightened as I always do.
A careful inspection showed the hub was not fully seated against the
shoulder on the shaft. It would tighten properly, then under use, the
hub would move closer to the shoulder and the belt would be loose
The shaft has a woodruff key that prevents the hub from turning
relative to the shaft. When you remove the old hub, it is possible to
drop the key. A magnet may help find it, or you can loosen the lower
shield if you can get a screw driver on all 6 screws that hold it in
place. I now carry a long screw driver and a magnet in my tool
kit in the car.
I removed that hub and put on the new one, this time tightening the
assembly with a 36 mm socket until the hub was seated firmly against
the shoulder on the shaft. This was done with all the washers but not
the belt. An impact wrench is good for this step so you do not bend
the rear pulley sheave using a screw driver in the notch to keep the
generator shaft from turning.
||Now we need to install the belt with the right tension. Be sure that
the pulley hub is seated against the shoulder on the shaft.
The belt tension is determined by how close to gether the sheaves are
contolled by the number of washers. Spare washers are saved under the
nut. The nut must be tight enough so there can be no movement of the
sheaves. This tension must be contolled by the washers and not the
belt. A trial assembly without the belt will show how much of the
shaft protrudes past the nut. With the belt on the same amount of
protrusion must be seen.
Here are the steps you can use to set the tension:
- Tighten the nut until the washers are firmly held between the
sheaves as discussed above.
- Start the car and run for a bit to allow the belt to move to its
- Check the tension. If too loose, move a washer from between the
sheaves to the storage position under the nut. If too tight, move
a washer from under the nut to between the sheaves.
- Repeat until you have 5/8 in. to 3/4 in. of slack when pushing the
belt with your thumb. The belt can be twisted about a quarter turn
when the tension is correct.
||The belts will stretch with use. Check and adjust again after 100
miles of use.
Check the temperature of the pulley after a short drive. If the belt
is working too much because there is not enough belt tension or the
nut is not tight and the sheaves are wobbling, then the pulley will
get very hot. This will lead to premature belt failure.
Carry an extra belt in your emergency kit. I carry two. Belt and
pulley problems are some of the most common reason for road side
repairs. If you are prepaired you should not need to have the car