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Notes From Changing the V-Belts

 
 
Old 09-11-2012, 02:58 PM
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bruce7
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Default Notes From Changing the V-Belts

Notes From Changing the V-Belts

Recently, I was hearing a belt squeal in the morning that lasted for a couple of
blocks then disappeared. It was usually heard when backing off the throttle to
shift or slow for a stop. My '97 993 has 67,000 miles and the belts had 24,000 miles
on them.

I thought about re-tensioning the A/C belt, but upon closer inspection I could
see some cracks showing between the ribs when the bright light of the sun
shown directly on the belt. I might have been able to squeeze a few more miles
out of the belts, but I had already purchased all 3 belts in anticipation of doing
a belt replacement job when the time was right so I decided to go ahead and
change them all out. I'm really glad I did too, because when I saw what the belt
wear was like after removal and under closer examination it was surprising.

This is the first time that I've done this, so I researched the procedure on
the Rennlist forum and on www.p-car.com. During the procedure I made notes
of any info that I thought might be useful for the DIY guy. This is a common and
frequent maintenance item, yet for the first-timer, there can be a lot of questions
and hopefully these notes plus the references above will answer those questions.

See this link for a collection of photos that accompany this article:

https://picasaweb.google.com/bruce.c...KOMpYbTg7yH8wE

Disclaimer - I have only done this procedure one time, so if anyone has a better idea
or a trick to contribute please don't hesitate to send comments.


1. Materials Required

You will need 3 belts as shown in the first photo (PNs are for a 1997 model).
Also get a 14" tie-wrap to hold the belt tension sensor out of the way. (Shown in a later picture).
And get 3 fan pulley bolts (PN 900-119-026-02), just in case yours need replacing.

2. Tools Required

The minimum hand tools needed to change the belts are shown in photo 3.
Also you should get a Krikit V-Belt tension gauge shown in photo 4.

Identification of tools

1 - 13mm socket 3/8 drive + extension + rachet
2 - magnetic pickup tool
3 - 5mm hex socket 3/8 drive
4 - 8mm socket 1/4 drive + rachet
5 - long flat-blade screwdriver
6 - 13mm x 12mm extra deep offset double box-end wrench
7 - 10mm triple-square socket 3/8 drive + breaker bar
8 - 24mm crowfoot 3/8 drive
9 - torque wrench 10-60 Nm 3/8 drive
10 - 24mm box-end combination wrench
11 - wire cutter

Notes on tool items.

Item 6. This wrench is made by Stahlwille. It has an offset of 75 degrees and
an offset depth of 25mm. It was sourced through www.SamstagSales.com.
The Stahlwille PN is 41041213.

Item 7. This socket is made by Snap-On. The PN is BLPXZNM3810.

Item 8. This wrench is made by Snap-On. The PN is FCOM24A.


3. Remove Air Filter Cover

Step one in removing the belts is to remove the air filter cover and move the clutch vent pipe
snorkel tube out of the way. When you do this you will then be able to swing a wrench to loosen
the A/C lock nut and adjuster bolt.


4. Wrench to Adjust A/C Belt Tension

The wrench called out in the tool list above is made by Stahlwille will enable you to adjust the belt
tension. Access is from the back side made available by removing the air filter cover.

I don't own any other offset wrenches, so I don't know whether they will or won't work. Snap-On
and Craftsman offset wrenches have an offset angle of 60 degrees vs the 75 degrees of Stahlwille.
I did check whether a standard 13mm wrench would work and it will not. As far as I know, Stahlwille
makes the deepest offset wrench available.


5. Use of the Magnetic Pickup Tool

Obviously, if you drop a nut you can use the magnetic pickup tool to retrieve it. But the tool has
another useful purpose. When removing the long bolts which hold the A/C unit down, you can use
the tool to hold the square nut while you remove the long bolt. This is easier than trying to fit your
hand down there to catch it and remove it.


6. Removing the Alternator Pulley Nut

The triple-square Snap-On tool used in conjunction with a breaker bar and the 24mm box-end wrench
make it an easy job to remove and install the nut on the alternator shaft. I think it is easier to use than
the Porsche 12-pt tool because of the greater leverage provided by the longer handle of the breaker bar.


7. Tie-Wrap the Belt Tension Sensor

Using a 14 inch long tie-wrap to hold the fan belt tension sensor out of the way makes the job of refitting
the fan belt and pulley easy. When done, use the wire cutter called out to remove the tie-wrap.


8. Remove DME Relay to Crank without Starting

Once a belt is in position, before final tightening, crank the engine a few turns
to help seat the belt in the pulleys, then do the final tightening.


9. Use of the Crowfoot to Torque the Alternator Nut

Using the crowfoot you can easily torque the alternator nut to the specified figure 50+5 Nm.
This nut is too important to not set properly with a torque wrench.


10. Mounting the A/C Belt and Compressor

This is probably the hardest part of the job, until you figure out the tricks, then it's not so bad.

Use the long flat-blade screwdriver to push the belt down below the crankshaft pulley past
the nuts that stick out.

Back out the adjuster bolt and lock nut on the A/C unit.

With all bolts removed, lift off the A/C unit and fit the belt around the pulley.
Not pivot the A/C unit up onto the base and drop in the long bolt shown in the picture as number 1.
Thread the square nut on but just get it started, don't tighten yet.

Now, with the large flat-blade screwdriver, pry the A/C unit forward as shown in the picture
until you can drop in the long bolt in position number 2. Thread the square nut on and tighten just a little.

Now evenly tighten bolts 1 and 2 to bring the A/C unit down onto the base until you can drop in the
long bolt in position number 3. There must not be any binding on the bolt or you won't be able to
get the square nut started threading. Once you can get the square nut on, tighten all 3 long bolts down
until you can get the short bolt started in position 4. Tighten it down but not all the way yet.

Now, check the tension in the belt and adjust it using the adjuster bolt and then tighten the lock nut.
From the full open position, I added about 1/2 turn to the adjuster bolt.

Tighten down all 4 bolts and recheck the tension in the belt. Recheck the adjuster and lock nut tightness.


11. Tension Gauge vs Deflection Method of Setting Tension

Conventional wisdom is to forget the tension gauge and use thumb pressure to eyeball the belt deflection.
For the A/C belt most people want about 1/2 inch deflection.

I did the belt change in 100 degree sun. At the time of install I measured 30 Kg tension on the A/C belt.
The following morning after about 15 miles of driving, with 12 hours of cooling down, at 70 degrees air
temperature, the tension measured 18 Kg. This is low so I retensioned it to 30 Kg. Deflection also seems to be about 1/2 inch.
My engineering side likes the repeatable accuracy of a measuring device, and when it jives with the
experienced mechanics rule-of-thumb, I have a high confidence that the adjustment is correct.

The alternator belt measured 15 Kg cold. Again, this is perfect and right on spec. My car had two .7mm shims
inside the pulley and two outside under the alternator nut.

One thing I learned is that the v-belt cold spec means the car should have set for at least 12 hours or
overnight. Driving just 3 miles in the morning and then letting the car cool for a half hour will not result in an
accurate cold measurement.


12. Belt Wear Signs

In the final photo you can see cracking in the alternator belt. All 3 belts had similar signs of wear.
Unfortunately, this wear is not readily visible when the belt is on the car.

Reading a v-belt trouble-shooting guide I found, it appears that heat is the most common cause of cracking
like this. This is not surprising considering the level of heat in the engine compartment.

I put around 20,000 miles a year on a car, so I think I will plan on changing the v-belts once a year.

I much prefer preventative maintenance to fixing a broken belt on the road.

-bruce

Last edited by bruce7; 09-28-2012 at 04:58 PM. Reason: edited for accuracy
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Old 09-12-2012, 12:39 AM
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ToSi
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Neat - if you have a torque wrench that works counter clockwise & fairly short XZN socket, you can use it to turn the shaft while holding the 24mm nut stationary w/ a box wrench & avoid the crowfoot. The advantage is a better grip on the fastener.

If you decide to use a crowfoot remember to keep it @ a 90deg angle to the head of the tq wrench so as not to alter the measured torque value.
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Old 09-14-2012, 02:45 PM
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bruce7
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Originally Posted by ToSi View Post
Neat - if you have a torque wrench that works counter clockwise & fairly short XZN socket, you can use it to turn the shaft while holding the 24mm nut stationary w/ a box wrench & avoid the crowfoot. The advantage is a better grip on the fastener.

If you decide to use a crowfoot remember to keep it @ a 90deg angle to the head of the tq wrench so as not to alter the measured torque value.
Hi ToSi,

Thanks for the excellent tip! I checked it out and it works beautiful! I agree with
you and would only recommend the crowfoot for torque wrenches that can only
work clockwise.

The Hazet wrench is one such wrench that can be used in either clockwise or
counter-clockwise mode. Please see the photos below to illustrate.

-bruce
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