Porsche IMS Bearings, Without the Panic

What the IMS actually does

The intermediate shaft sits inside the engine and carries drive from the crankshaft to the camshafts through a pair of chains. It is a simple piece of engineering doing an unglamorous job, and for most of the life of these cars it does that job quietly.

At the end of that shaft is a sealed bearing. If the bearing wears out, the shaft no longer sits where it should. Camshaft timing walks away from crankshaft timing, valves meet pistons, and the repair stops being a repair and starts being an engine. That is the whole reason for the reputation, and it is a fair reputation. What is not fair is applying the same level of worry to every single car.

Three bearings, and yours is one of them

Porsche used three different intermediate shaft bearings across the M96 and M97 engines, and they do not carry the same odds. This is the part worth knowing before you spend a dollar.

The car in the shop this week is a 1999, which means it left the factory with the dual row bearing. It is the sturdiest of the ones that can actually be serviced. That does not make it immortal, and dual row bearings do fail, but the owner of a 1999 and the owner of a 2003 are not looking at the same problem.

• /1997 to 1999: the dual row bearing. Failure rates are commonly put around one to two percent.
• /2000 to 2005: the single row bearing, and the source of most of the horror stories. Commonly cited around eight to ten percent.
• /2006 to 2008: a larger bearing, back down around one percent, but not serviceable without opening the engine.
• /The changeover happened partway through the 2000 model year, so a 2000 car can be either one. Worth confirming rather than assuming.

How to tell where yours stands

You do not need a crystal ball. A failing bearing tells on itself, and the cheapest diagnostic tool you own is the oil filter you were going to throw away anyway.

Cut the filter open at every service and look at the pleats. Pull the drain plug and look at the magnet. Metal where metal should not be is the signal, and catching it early is the difference between a bearing job and an engine.

• /Fine metallic glitter caught in the oil filter pleats
• /Shavings clinging to the drain plug magnet
• /Small black plastic flecks, which come off the bearing seal as it breaks down
• /Oil weeping from the intermediate shaft flange at the back of the engine
• /A new noise from the back of the engine that was not there last month

The smart time to deal with it

The bearing lives behind the transmission. Reaching it means the transmission comes out, and that is the single biggest line on the bill. A clutch job means the transmission comes out too.

Do them at the same time and you pay that labor once instead of twice. This is why the honest answer to when should I do my IMS is usually when the clutch is already due, rather than on a calendar.

If your car is an early dual row and the clutch has plenty left, watching your oil carefully is a legitimate choice, not a dodge. If it is a 2000 to 2005 single row and the transmission is coming out for any reason at all, that is the moment. Do not put it back together without dealing with the bearing.

What I would tell you on the phone

Tell me the year and the mileage and we can narrow it down in about a minute. Bring the car in and we can look at the filter and the magnet and know a great deal more than an internet thread will tell you about your specific car.

If you are shopping for a 996 rather than already owning one, do it in the other order. A pre-purchase inspection before the money changes hands costs a fraction of what finding out afterward costs, and the intermediate shaft is exactly the sort of thing it exists to catch.