Tensioning Belts - An Introduction

Owning a 944 pretty much means knowing something about the timing belts. This page is intended to provide some insight on tools & methods for setting the belt tension.

Its funny how these belts exist in countless other cars but on the 944 they take on a whole new level of dread. Some feel the belt failures are the 944's Achilles heal while others see them as no big deal. No matter where you stand in this mix, there is no question that the 944's belts require a bit more maintenance than other cars. Belt maintenance, and specifically the tensioning of the timing belts, is not as straight forward as you might hope. The specialty tools, particularly for Porsche's recommended method, are expensive. There are alternatives but as you might expect there are also problems with these approaches and this page is an attempt to highlight exactly what those problems are.

Below is an options diagram to illustrate the different approaches.

Notes for chart above...

The Krikit will work reasonably well on the cam belt (83 through 86 944 only) but is not well suited to the balance belt. The Krikit's operating range will just barely read the low tension setting needed for the balance belt. Is this a show stopper? Not usually, one casual method of setting the balance belt is to set the belt by feel and then observe how it tracks with the engine running - too loose and it will flop against the belt cover, too tight and it will make an irritating whine. Some "ball park" adjustments can be made with the krikit and this approach.
Deleted Note.
The balance belt can be set by feel.
Here is a link to the steps for using the Porsche 9201 tool.
The 920X can only be used on engines that have the updated waterpump. Here is a link for using the 920X.

Above is a sketch to illustrate the options available to you. The method that you use is based on which specialty tools that you have on hand. The 9201, is a Porsche tool that is roughly the size of a pack of cigarettes and, with a little practice, will provide a reliable reading of your belts. The 9201 price is approximately $680. The 920X is a tool that I make. It costs approximately $150. The Krikit is about the size of a marker pen and costs about $25. It can only be used on some Porsche models and is not well suited to the balance belt. Still, it is very popular with some.

Tensioning Belts - More General Info

First, getting access to the belts is a challenge in itself. Above is a photo of an 85.5 NA, the other models are slightly different but equally difficult.

Here is a drawing of the belt layout used in the 83 through 86 944. Porsche recommends these belts be replaced every 30,000 miles and be re-tensioned at about 1500 miles following replacement. Porsche offers a couple of tools to set the belt tension and you should be able to pick these (below) up at your local dealer for about $700. If this seems reasonable, get the maintenance manuals while you're there (for another $430) and forget about trying to do this little job on the cheap.

The Twist Method

This method uses no special tension measuring tools. It is really for the more casual mechanics but any discussion of the various tensioning methods must include at least a mention of this procedure. Essentially, we are going to set the cam belt tension to a point where the belt can be twisted to 90 degrees from its normal tracking position. This is done with the thumb and index finger of an average strength man. This should be done at a point along the belt midway between the cam gear and the crankshaft gear, along the upper span and the timing belt idler pulley must first be removed.

Do I recommend this approach? Umm no, but if you're going to guess at your cam belt tension, this beats nothing.

Which cars will this work on? Only the 83 through 86 944s and 924S.

Using the Krikit

Below is the Krikit and the belt setting that should be used with the Krikit.

I don't have studies or lab analysis to prove that this tool works but there are many, many 944 owners who use this tool and they frequently recommend it in the Porsche community discussion forums. While I personally don't recommend the Krikit, I will help you to use it.

Note: You should be familiar with the specific steps for setting the tension of your belts - I'm only touching on the general steps here to demonstrate the tool. One place to look for this info would be Clark's Garage. Clark's procedure is largely taken from the Porsche workshop manuals, and is centered on using the Porsche 9201 tool. Still, the general procedure is the same.

First, a couple of photos of how to orient the Krikit along the belt. Above photos are of the cam belt and the balance belt. Note that on the photo of the balance belt (which has "nubs" on both sides), the contact portion of the indicator arm is directly over one of the belts nubs. This is important for an accurate reading. When you apply thumb pressure the belt will deflect and you will see the indicator arm raise up and a click can be felt/heard. When you feel this click, immediately release the pressure and read where the indicator arm intersects the scale.

The above reading is 27 Lbs and very close to the correct setting for the 944 balance belt.

Side note: when I first used with this tool, I was concerned that the Krikit would not accurately measure below the lowest scale mark of 30. This should be a concern by anyone considering the Krikit as it is seldom good to use a pressure measuring device at or near it's limits. If you haven't used the tool before, you should make several readings (without altering the belt tension) until you begin seeing consistent readings - it may take a few tries to get the hang of it.

Now, on to the actual belts. The ideal place to measure belt tension is at the center of the longest span. To create a long span, I have removed the upper timing cover (for access), the timing belt idler pulley and water pump guide rail (available only with the updated water pump). Notice how that when I apply thumb pressure through the Krikit, there is a space (see arrow) between the spanned portion of the belt and the other area of the cam belt. This small space is important, without it, you will not be accurately measuring the belt's tension.

The Krikit quickly tells me that my timing belt tension is correctly set at 40 lbs. I make a this reading a couple of times to be confident that I am getting a good reading. If the reading is low or high, I make the needed adjustments and use the Krikit to make another reading. Note too, how easily the small size of the Krikit works to fit into this very tight area. This is a noteworthy advantage over the other tools.

I haven't mentioned it but you should have your cam positioned at about a tooth before TDC. If you're making changes to the the timing belt tension, it's best to rotate the crankshaft backward until the cam is at the 1-1/2-tooth-before-TDC position. Doing this moves the small amount of belt slack to the upper span of the cam belt. Then recheck the tension using the Krikit. This "back-positioning" of the cam is not needed for adjustments to the balance belt. My photo above is only meant to show the different marks. In this photo, the marks are not correctly aligned.

Above, you can see my attempt to get a reading of the balance belt. As before, I've removed the balance belt idler roller to create a long, unobstructed span. In this case my tension was so low that I got an invalid reading. This is apparent because the indicator arm is extended against the stop, see below.

This was easily changed by tightening the balance belt tension and simply rechecking with the Krikit. I then repeat this tighten-then-measure cycle until I had the correct tension. Most people are surprised at how loose the correct tension on the balance belt is. I've found that it should be no higher than 28 pounds else there is a distinct (and irritating) belt whine. With that, I re-installed the idler roller and prepared for a engine-running inspection of belt operation.

With the balance belt re-tensioned, I only need to get the idler back in place before starting the engine. Here you can see that I'm re-setting balance belt idler roller to the specified .5mm - it should not actually touch the balance belt (except during operation).

These photos make the access appear easier than it actually is. Working in this tight area is a pain, but you'll get the hang of that too with a little patience. You can see here (above) that I'm using an older version of one of my roller wrenches. A standard wrench will not fit, at least not from many approach angles. What's worse, as you tighten the anchor nut, the off-center, adjusting nut tends to turn along too and alter your carefully chosen setting. You'll probably not use this thin wrench for anything else, but for carefully setting the belts, it sure saves some aggravation.

Other Notes:

This is the belt layout for many others of the 944 series. In the center is a device known as an auto-tensioner. If it has a fresh spring, it will get your cam belt "in the neighborhood" of a correct re-tension setting. Be aware though that the springs on 20 year old cars are often way out of tolerance.

Here is the video clip of a a too-tight balance belt.

Here is a link to more info on the balance shafts.

Above, I mentioned the Porsche recommendation for belt change intervals. There is some controversy concerning how often the belts should be changed, Gates (a company who make belts) recommends a longer interval. This clipping (below) is taken from Gates' manual on recommended belt change intervals.