If there is a Porsche 944 in your garage or your future you may want to study up a little on the timing belts. Yes, there are two belts and belt problems have plagued the 944 all through its life. Taking care of the belts is not really that tough though. Basically, the belts have a life-span of about 30000 miles or about 3 years. So if you're a 944 owner, you need to learn a little about servicing the belts or find a mechanic who can perform this work. This web page, and really all of our pages, is for the Do-It-Yourselfers who have enough confidence to get in and take care of things for themselves.
Belt servicing is pretty straight forward but there are a few complications. For instance, once a new cam belt is installed, it needs to be re-tensioned after about 1000 miles - this is because the new belts stretch out a bit and need to be tightened up. Even with the need for re-tensioning, a new cam belt must be set tighter than a used belt. If you fail to perform the re-tensioning a belt failure is almost certain as a loose-belt-failure (nubs stripped off of the belt by the crank cog). The next most common failure is due to age (over 3 years) or excessive miles (greater than 40,000).
Another complication are the different configurations used on the various model years. Porsche introduced several design changes to the cam belt's mechanism. The improvements were all aimed at making the belt more reliable.
There are a variety of theories as to why the 944 has had so many belt problems. I think the best of these has to do with the expanding aluminum block coupled with the fact that the 944's engine is quite large (when measured from the cam to the crank). With so much aluminum between the two, there a great potential for expansion as the engine warms up. The cam belt will stretch a little but not nearly as much as the aluminum will grow. So, the tension must be set loose enough so to compensate for expansion but tight enough so that it doesn't skip on the cam shaft and jump out of time on the coldest of mornings. If too tight, the cam belt will place undue stress on the waterpump (waterpump failures are also common on 944s) or even break the cam belt completely.
If you've done the process as tensioning as Porsche recommends, you will find that the sweet-spot of belt tensioning is a very small - its very easy to get this wrong. Getting it wrong won't mean a next-day catastrophe, failures don't happen that quickly. More likely, it will mean the difference in a belt that lasts 30000 miles and one that has problems, resulting in a serious repair after only 10 or 15000 miles.
There are four different tensioning tools that you can use. The best of these is the Porsche recommended tool, the P9201. It is the gold standard for belt tensioning, and unfortunately, carries a hefty price tag with it (approx. $650). If price is not a problem, get the 9201 and read about how to use it in the Porsche Work Shop Manual (WSM). Even if you don't plan to use the 9201, the WSM is a good place to read the process of tensioning the "drive belt." There is one small limitation with this tool; it should not be used on 928s prior to midyear of 83. This is due to the early 928s (78-83) coming with a flat notch shaped cam belt. This belt is thicker than the High Torque Drive (HTD) belt used from midyear 83 on. The difference in belt thicknesses alters the 9201's measured tension. The Porsche provided spec for tension of the HTD belt is not correct for the earlier belt and Porsche did not provide a spec for 9201 use on the early 928's.
One alternative to the 9201 is our 920X. It is very accurate, and uses a machinist's gauge to read deflection values. This is the same basic approach as that of the 9201 but the 9201 is hand held while the 920X mounts directly on the engine. The Porsche tool can be used on other belts and even other models (except as noted above). Both tools are very sensitive and require the disciplined approach of an experienced mechanic. Note: the 920X does not rely on the belt thickness, so is not limited as noted above for the P9201. More info here.
Next is our 9131-944. This tool was inspired by the forerunner of the 9201. The P9131 was the prescribed tool for tensioning of the early 928's cam belt (the 928 is essentially a V8 version of the 944's engine - and has many shared parts). The P9131 is a simple tool that uses a spring and sliding scale to measure resistance to twisting pressure placed on the belt. In this way it can assess the tension of the belt. We created the 9131-944 to do this same thing for the 944. It costs about $50 and is fairly easy to use. It is not as accurate as the tools above. Even so, it is our best seller and offers a good, quick assessment of your tension with a simple setup.
And last is the Krikit. The Krikit is about the size of a marker pen and costs $25. It was designed to be carried in your shirt pocket and used for measuring the tension of v-belts of air conditioners and fans. Desperate for an alternative, 944 owners started using this tool a few years ago. It is better than nothing but can only be used on the early 944s (83 thru 86) models - the later models have a spring tensioner hardware that interferes with the use of this tool. Also, the Krikit's scale just barely goes low enough for use on the balance belt. Demand for this tool has dropped to near zero, so we expect to stop offering this tool in the near future.
For 944s, you will also need a 27mm (or possibly a 24mm) thin wrench. A little background on the thin wrench... in the early 944 cars Porsche used all-steel rollers and idlers that had a 24mm offset nut. As stated earlier, Porsche went through several design changes to address problems and one of the first of those was to swap the 24 for 27mm rollers and idlers. Cars that were serviced by Porsche got the upgrade, so there are almost none of the old 24mm hardware around anymore. Here is a pic of our 27mm thing wrench.
We also have a 24/27 combination thin wrench if you're unsure about which rollers you have installed.
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 1000 miles following replacement.
This is the belt layout for many others of the 944 series. In the center is a device known as an auto-tensioner or spring tensioner. It was designed to get your cam belt "in the neighborhood" of a correct re-tension setting. Be aware though that the springs are now over 20 years old and are often way out of tolerance.
After belt maintenance the balance belt user sometimes will hear an engine-speed-dependent whining sound. This is not a serious problem but may be an irritating one. Generally, this is associated with the over-tight balance belt or the use of a non-standard cam belt.
Aside from getting the correct tension on the balance belt, there are a few contributors to the problem:
Here is the video clip of a a too-tight balance belt.
Here is a link to more info on the balance shafts.
