Porsche 944 and 951 Timing Belt Service – Doing It Right
The recommended timing belt replacement interval for the 944 engine is every 30,000 miles, to which we would also add a time interval of 3-5 years.
As the timing and balance shaft belts being rubber, deteriorate over time, these vehicles are now rarely driven more than 3,000 to 5,000 miles per year.
Timing belts are made of very durable rubber, with layers of cord to prevent stretching. This arrangement provides years of trouble-free service and precise valve timing. Eventually, the rubber and cords begin to deteriorate. Our rule is 3 -5 years at most.
Due to the normal expansion and contraction of the 944 engine, Porsche recommends that the engine is at room temperature (68 degrees) when replacing the timing belts. Installing the belts at a different temperature will cause an incorrect belt tension adjustment because the engine expands and contracts as it heats and cools.
Important Service Note – New belts should be re-tensioned after their first 2000 miles of use and again after another 15,000 miles.
Why – Engine Damage
All 944 engines are interference engines. The valves and pistons have an overlapping space on interference engines, hence the name interference. If the piston is at the very top of its stroke and the valve is fully open, the valve and piston will collide. The timing belt controls the opening and closing of the valves. The Porsche 944 timing belt is made of rubber and therefore is susceptible to normal wear and tear.
Additionally, it can loosen over time or even completely snap if the rubber becomes torn, brittle, or excessively worn down. Because the engine is an interference engine, when the 944 timing belt breaks, it sends the valves and pistons colliding with each other. The end result is bent valves and potentially damaged pistons. Replacing valves and pistons will require the engine to be opened up, which is labor-intensive and expensive.
Service Plan – Design Changes
The 944’s timing belt design has been upgraded several times since the first car rolled off the assembly line.
Some of these changes were field fixes, and others were production updates.
The updates began in Porsche 944’s first model year, with most of the updates occurring between 1984 and 1986. Almost all the cars have now had the updated parts installed, the most common being the use of the 951 water pump, with guide rail and outlet block-off plate. But you might be surprised from time to time by what you find out there. Original cars with super low mileage and only the timing belt changed or aftermarket parts installed, even balance shaft belts installed incorrectly, result in significant engine vibration.
Each of the following parts have been changed as part of the service upgrade process:
• Belt design
• Camshaft belt tensioner
• Balance shaft belt preload tensioner
• One-piece timing belt cover modification
• Two-piece timing belt cover
• Shaft seals
• Water pump
A Word About Water Pumps
We are frequently asked about reusing water pumps on the engine when the timing belt is serviced. And while that might sound like a good idea, remember what the pump is, and what the consequences are of failure. Water pumps circulate coolant through the engine. They are generally a pretty common maintenance item for all cars.
Why do water pumps fail? Water pumps naturally fail over time from wear and tear and old age. The Porsche 944 water pump fails for a few different reasons. First, the internal bearing can go bad, which will cause a “bearing” noise from the water pump. Secondly, the impeller can separate from the shaft, or the shaft seal can go bad, which will cause coolant leakage. Lastly, the pulley connecting the water pump to the timing belt can slip or break and cause engine failure.
However, they are known to fail a bit more frequently on the Porsche 944. The 944’s water pump is driven by the timing belt, which is also why we recommend replacing them at the same time. A water pump issue necessitates the removal of the timing belt and engine covers to replace, so might as well do it correctly the first time. The cost of a pump is far less than the cost of an engine or engine repair.
Quote It Right – Don’t Get “Slapped”
We must know what you are buying when pricing a timing belt replacement. Some companies quote a phone price for replacing the belt alone, in a less than ethical way to get the car there. Quality auto repair shops refer to this as a “belt slap” (you’ll also hear the “slap” term on shops that just “slap on” brake pads without the full service. This may seem like savings until they call back with the real cost.
Perhaps worse is only replacing the belt, only to have another component fail, for instance, if the water pump fails a few thousand miles after the timing belt is replaced. Repair means another full disassembly, and the water pump can actually cause the replaced timing belt to break, causing engine failure.
Another problem is a seal that starts to leak after timing belt replacement. The seal could have been replaced for a minimum cost while the timing belt was off. Now many of the same components must again be removed. Worse, the oil from the leaking seal can ruin a new timing belt. Remember, you never get more than you pay for.
The Only Correction Is Prevention
An once of prevention (as in a replacement of the timing belt, BEFORE failure) is worth a pound of cure.
If your Porsche qualifies, and the timing belt has not been replaced in the last 3-5 years, we strongly advise you do it proactively.
Do not wait, time is engine. Your engine.
Need More Help?
We hope we’ve been able to shine some light and help you better understand what exactly a timing belt is and what can actually go wrong with them. And more importantly, how to prevent that from occurring! To discuss the best approach for your car, give our service team a call us or email email@example.com.
Questions, or if we can be of help in any way with service on your Audi, BMW, Mercedes, Mini Cooper, Porsche or other European import, please contact us.
Our team of Service Specialists is here to help, for even the newest autos! (207) 882-9969.
Knowing, not just “doing,” that’s the Atlantic Motorcar Center way.
The Atlantic Motorcar Center Service Team