Whether you are new to the Porsche world or a die-hard enthusiast, you have probably heard of the dreaded intermediate shaft bearing or IMS bearing failure.
This is a terrible stain on the reputation of what is otherwise beautiful, exciting, and reliable sports cars. Luckily, only a few models have any issue with this particular failure.
In fact, there are a few Porsche models affected by the IMS bearing issue. Porsche models most affected by the IMS bearing failure are:
- 986 Boxster models.
- 987 Cayman & Boxster models up to engine number 61504715
- 996 models (not including GT and Turbo models)
- 997 3.6ltr with M96/05 up to engine number 6950745
What is IMS bearing on Porsche?
IMS stands for 'Intermediate Shaft' or IMS bearing for short. The IMS bearing's main function is to support the intermediate shaft, which is located at the back of the engine where the flywheel is located. The intermediate shaft is used to drive the camshafts indirectly off the crankshaft.
First, Porsche sports cars have been traditionally powered by horizontally opposed engines, commonly called boxer engines. As mentioned above, the IMS bearing issues typically impact the 911 Carrera and Boxster.
These incredible pieces of engineering work differently than normal internal combustion engines, as their pistons push outward instead of up and down, creating a very compact power unit. At the time, this was Porsche's first offering of a water-cooled boxer variant to the market. So, you may be wondering, what exactly is an IMS bearing?
The letters stand for Intermediate Shaft, a tube that runs from the front pulley side of the engine to the rear valve timing assembly. The IMS powers either three or five timing chains, depending on whether it is a first or second generation of the Porsche M96 power plant.
At the end of the tube are sprockets that drive the timing chains around the camshaft gears in the cylinder head to keep the valve assembly in time with the crankshaft. In short, the IMS bearing is the glue that holds the entire engine timing assembly together.
What year Porsches have IMS bearing problems?
Porsche models such as the 996 and 986 models, produced between 1997 and 2004, have the most IMS bearing failures.
However, this is not the case with high-performance models, like the turbo. If you are concerned about IMS bearings issues, read on to learn more.
Symptoms of a Bad IMS Bearing
We often get asked: "What are the symptoms of IMS bearing failure on a Porsche?"
The most common symptoms of a bad IMS bearing on a Proche include metallic debris in the oil, oil leak at the rear of the engine, and engine noise coming from the back of the engine.
- Oil leaking between the engine case and the transmission: Horizontally opposed engines naturally have some crank wobble under heavy load that causes the rear main seal, or crank seal, to wear prematurely and leak engine oil on the IMS cover. This is located directly below the crankshaft. Porsche originally designed the M96 IMS bearing to be known as a dry bearing, which means it has enclosed grease and is not lubricated by oil flow from the oil pump. Oil can get into the bearings grease and dilute it, causing the assembly to overheat and fail.
- Whining, rattling, or grinding noise coming from the engine at idle: Engines make strange noises sometimes and, from a professional standpoint, could stem from what feels like an almost infinite number of reasons. Being able to narrow down those reasons comes only from experience. Rotational noises are very distinct and could be as simple as a bent brake rotor dust shield, or it could be the engine singing its final tune before complete detonation. If you encounter these noises on a car you are looking to purchase, proceed with extreme caution.
- Metal particulates in the engine oil: A good practice if you are looking to buy a used car from any manufacturer is to take the car for a pre-purchase inspection. Find a local shop specializing in Porsche and ask the owner to meet you there so you can have the car put on a lift and inspected. Most automotive shops perform this type of inspection routinely and charge around $150, depending on the area, or roughly 1-hour of labor. There is an emphasis on finding a Porsche specialist because, with these cars, you really need someone who knows the brand. They may miss important details that can change the value or even your interest in purchasing the vehicle.
What Happens If the IMS Fails?
To put it bluntly, if the IMS bearing fails, so do many of your dreams. IMS failure is considered catastrophic in the mechanical world, which means it will probably never run again.
The M96 is a high interference motor, so the cylinder head to engine block timing is crucial to its operation and survival. Failure causes the timing chains to skip or even break, making the Pistons come into contact with the intake and exhaust valves, slamming into each other, breaking apart.
The oil pump then sends these chunks of metal to every corner of the engine damaging everything they come in contact with along the way. You now have a Porsche paperweight; this is the part that makes new buyers scared of these truly great cars.
IMS Bearing Repair Cost
If you own a 911 or Boxster with an IMS failure, you have really two options: replace the engine or sell the car for parts non-running. Refurbished engines range from around $10,000-$15,000 for a 911 and $5,000 to $8,000 for Boxsters; this does not include installation, which takes about 8 hours with a Porsche familiar technician.
Depending on your area and the shop rate, this can be from $1,000 to $2,000, not to mention all the small things like fluids, old rubber hose, plastic clips, rusty exhaust bolts, etc. and small parts that never survive engine out operations that all carry the notorious “Porsche Tax."
You can also save money by purchasing a new Porsche IMS Bearing online.
How to Avoid a Porsche IMS Bearing Problem?
A ray of hope in this otherwise scary campfire story of what can happen when you buy the wrong car is there are many ways you can keep IMS bearing from ever being an issue. Porsche factory maintenance specifications state that the bearing should be serviced every 60,000 miles or about as often as the clutch.
If you are purchasing a car, always ask for any records the owner has to see if the bearing has been serviced properly. Make sure to get that pre-purchase inspection as well because this is not a DIY job. Special tools are required, and the engine is toast if not performed correctly. If you can not find service records available, then you should factor the cost of replacing the IMS bearing into the initial price of the car.
Permanent IMS Bearing FIx
You have options with either factory Porsche replacement parts or several aftermarket companies that make exceptional and arguable better-designed hardware.
LN Engineering is the industry leader in these retrofit kits with much stronger roller style bearings and even “true fix” solutions that replace the IMS with an oil-fed lubricated bearing instead of the factory dry style. In any case, the IMS bearing is a wear item with long service life, so it is not something to be overly concerned about.
If you own or are in the market for a 996 Carrera or a 986 Boxster, you should not worry. These are great cars that have gotten a bad reputation for being unreliable. Porsche's IMS was partially redesigned in 2002 and completely redesigned in 2004 for the new M97 engine.
In my professional opinion, the IMS failure is mostly internet ghost stories of poorly maintained cars. This fear has driven the prices way down, which means you can enjoy a wonderful sports car at an affordable price.