Using the 920X Belt Tensioning Tool

Introduction: this short document contains a step-by-step guide for using the 920X belt tensioning tool manufactured by ArnnWorx Specialty Tools. This tool is desi= gned to assist with the accurate tensioning of both the cam belt and balance bel= t on most Porsche 944s. These include all models of the 944na, 944 turbo, 924S &= amp; 944S. I believe it will also work on the 968 but this has not yet been verified.

Below are two procedures to follow for the cam belt. T= he first is preferred as it was used for development of the tool and will yield more accurate results. The second is an alternate procedure and is more clo= sely modeled after that laid out in the Porsche Workshop Manual. It is slightly easier than the preferred method as it does not require the distributor cap= to be removed. All adjustments are to be done on an engine that has completely cooled and is as near ambient temperatures as is possible.

While the 920X is a very sensitive and accurate device= , a number of things can inadvertently lead to faulty or inconsistent readings.= The procedural steps must be followed closely to ensure proper use. Please read through these steps and familiarize yourself with the information. If you h= ave questions, contact me and I will help.

Before beginning, confirm that you have the specialty = and hand tools needed for this procedure. Generally, these include:

&nbs= p; 27mm thin wrench &= nbsp; &nbs= p; 3/8^th in. drive breaker bar <= span style=3D'mso-tab-count:1'> 19mm, 3/8th drive socket

&nbs= p; 10mm wrench &= nbsp; &nbs= p; Large crescent wrench #2 Phillips sc= rewdriver

&nbs= p; ½ in. drive breaker bar 24 mm, ½= ; in drive socket &= nbsp; Pin wrench (87 and later)

Cam Belt - Method 1 (preferred)

Place a good measure of force = on this wrench; you will only be able to move it by about 2 degrees before the parking brake prevents further rotation. This step places the beltR= 17;s slack on the lower span of the belt and is very important to an accura= te reading.
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Loosen the small screw on the= gauge (at approximately 1:00 o’clock position and rotate the outer gau= ge ring until zero is at the 12:00 o’clock position. Tighten the ri= ng screw.
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WARNING: Damage will result to both the engine and the 920X if the engine is started or even turned over while the tool is installed. = <= /span>
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The worksheet form will help calculate the correct tension for your car. Record the initial reading of= the gauge in box 1 of the card. Add the deflection value printed on the card and enter your result in box 2 o= f the card. Copy that result into boxes 3 and 4. Add and subtract the tolerances (as stated on = the card) and enter your corresponding results in boxes 5 and 6. The value in box 2 i= s the midpoint of the recommended tension range and therefore the ideal sett= ing. In subsequent steps, attempt to reach this value, but do not accept readings that are outside of those values seen in boxes 5 & 6. =
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To do this, loosen bolts A & B and push down or pull up on the autotensioner. Using a pin wrench will make this easier. Once the 920X gauge shows the correct reading, tighten the tensioner bolts A & B= .

Cam Belt - Method 2

Note: Spark plugs must be installed for this method.
WARNING: Damage will result to both the engine and the 920X if the engine is started or even turned over while the tool is installed. =
Add the deflection= value printed on the card and enter your result in = box 2 of the card. Copy that r= esult into boxes 3 and 4. Add and subtract the tolerances (as stated on the card) and ent= er your corresponding results in boxes 5 and 6. The value in box 2 is the midpoint of the recommended tension range and therefore the ideal setting. In subseque= nt steps, attempt to reach this value, but do not accept readings that are outside of those values seen in boxes 5 & 6.

= 10. While observing the gauge, hold the off-center pivot roller with the thin wrench = and loosen the 19mm securing nut. Once the 19mm nut is loose, you will observe = how altering the position of the thin wrench immediately changes the 920X readi= ng. Use the gauge’s reading as a guide and position the thin wrench to achieve the correct tension. Once there, tighten the 19mm nut. Some patience and anticipation is needed here as tightening the 19mm nut invariable alters the tension reading somewhat. Try to achieve the desired reading without go= ing excessively beyond it. Also, all readings (except the one made with the reference bar in place) must be double checked after snapping-the-gauge; re= ad about this below. Note: the photo above shows an earlier engine, if you hav= e an 87 or later model, you will need to adjust the belt tension using the mechanical auto-tensioner.

To do this, loosen bolts A & B and push down or pull up on the autotensioner. Using a pin wrench will make this easier. Once the 920X gauge shows the correct reading, tighten the tensioner bolts A & B.

Balance Belt

For this procedure, the engine does not need to be in = any particular position. Unlike the procedure for tensioning the cam belt, ther= e is to be no “pre-loading” or deflection to be placed on the balance belt other than that provided by the 920X tool. It is assumed that the balance shaf= ts are not binding and aside from the belt would freely turn.

Evaluate the condition of the balance belt for damage or excessive wear. Replace if warranted. Note: a properly adjusted balance belt will, to most people, seem very loose. While inspecting the belt, take note of how little tension is used.
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Gently pull down on the sled = and rotate it under the balance belt. Rotate the outer ring of the gauge so that zero is at the 12 o’clock position.
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Add the deflection value to yo= ur box 1 f= igure and enter the sum in = box 2, 3 and 4. Do the simple math indicated for boxes 5= and 6. Box has the ideal tension setting and boxes 5 and 6 hold the minimum= and maximum settings.
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Observe the gauge and slowly alter the position of the thin wrench until the i= deal reading is reached. Snap the gauge again to ensure a valid reading and make any last adjustments to reach the ideal setting.

The pro= cess of measuring tension is reasonably straightforward. We are attempting to move = the belt’s slack to one span and along that span place a deflecting force. With the force in place we will then measure the amount of deflection. There are a couple of variables that complicate this approach. First, getting a consistent amount of slack onto one span is difficult; for the cam belt we = must rely on the engine’s resistance to rotation to help us. Engines diffe= r, albeit slightly and that difference can result in variations in readings. T= his is true using the P9201, 920X or any tension-measuring instrument. Second, = to a small degree, the belt can be stretched. You may notice how the 920X’s needle rises quickly when increasing tension and a bit slower when reducing tension. We attempt to minimize the effects of this by trying not to “overshoot” our tension adjustments. And last, the 920X itself = has some small resistance to change. While this is small, we are also attemptin= g to measure very small deflection forces and given our tolerances, this is sufficient to give false readings. Luckily, there is an easy way to correct= for this – something I refer to as snapping-the-gauge. To do this, simply lift the small knob at the top of the gauge and release it – it will = snap back. You need only lift it about 1/8^th of an inch. Each time yo= u do this, you will see that the reading change slightly. Do this 2 or 3 times u= ntil you feel you have reached an average. That average is your final reading.

&n= bsp;

Caring for your 920X

= The tool is constructed using both mild and stainless steel. The mild steel surfaces are coated using a process of acid etching. This gives the fixture body a soft black finish and that finish helps to hold a light machine oil.= The oil helps with the function of the tool and prevents corrosion. The tool wi= ll however, rust in the absence of the oil and the oil can be removed in the course of routine handling. After each use, all surfaces of the 920X fixtur= e body (inside and out) should be re-oiled using WD-40 or a light gun oil. No lubrication is needed for the gauge.

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Reading the Gauge

Here is an example of how to read the gauge.

Worksheet Form

Tensioning of Used Cam Belt<= span style=3D'mso-tab-count:3'> &= nbsp; &nbs= p; Tensioning of New Cam Belt

Box 1=

Box 1=

Initi= al Reading (w/ Ref bar) &= nbsp; Initial Reading (w/ Ref bar)

Add deflec= tion value +.198 &= nbsp; Add deflection value = +.173

Box 2=

Box 2=

Ideal Ten= sion Setting è &= nbsp; &nbs= p; Ideal Tension Setting è

Box 4=

Box 3=

Box 4=

Box 3=

+ .009 = = -.009 = + .007 = = -.007=

Box 6=

Box 5=

Box 6=

Box 5=

= Minimum &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; = Minimum

&= nbsp; &nbs= p; =

&= nbsp; &nbs= p; &= nbsp; &nbs= p; Maximum &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p; Maximum

Tensioning of Balance Belt &= nbsp; &nbs= p;

Box 1=

Read= ing (w/ Ref bar)

Add deflection value +.180 &n= bsp;

Box 2=

Ideal Ten= sion Setting è &= nbsp; &nbs= p;

Box 4=

Box 3=

+ .010 = &nb= sp; -.01= 0 =

Box 6=

Box 5=

= Minimum &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; = &= nbsp; &nbs= p;

&= nbsp; &nbs= p; &= nbsp; &nbs= p; Maximum &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p; &= nbsp; &nbs= p;