by Mike Emery – Perfection Auto Works, Tucson, AZ
Do you have questions about the Troubling Porsche IMS bearing? You’re not alone. By now, most Porsche 911 owners have heard about the Porsche IMS bearing issues that have plagued these engines for years. However, if you own or are considering purchasing a 996 or 997 generation Porsche 911 (excluding Turbo models), or a 986 or 987 generation Porsche Boxster, and aren’t already aware of the “IMS bearing upgrade” then we urge you to keep reading because the information you’ll find here could save you TONS of money.
There are many search results on the internet regarding this subject, and many either have conflicting information or just seem to confuse the topic even more. Many readers are still left wondering about the real answers to their questions. “What causes IMS bearing failure?” “How can you tell if your Porsche IMS bearing needs to be replaced?” “Can IMS bearing failure be prevented?” “What is the Porsche IMS bearing failure rate?” We’re here to help you understand the problem just a little more. You want to be informed and you want to know how to protect your Porsche from premature disastrous engine failure. caused by a failed IMS bearing. Here is everything you need to know about the Porsche IMS bearing issue.
First things first, a little basic information is in warranted before we get down to the bone.
If you read the words “Disastrous catastrophic engine failure” above, your first thought might have been to wonder exactly how such a relatively small component has the potential to DESTROY an entire engine, instantaneously, and almost with no warning. Without getting heavy and to technical, we’ll go over what an IMS bearing is and what its function is.
First, “IMS” stands for intermediate shaft. The intermediate shaft is a geared shaft that runs through and extends out from the front and rear of the engine. With those gears, the function of the intermediate shaft is to use the mechanical rotation of the engine’s crankshaft to drive the camshafts on either side of the engine. The actual intermediate shaft itself, however, is not the root of the now well-known and infamous 996 and 997 IMS-related “engine problems.” The basic design and use of an intermediate shaft was not a new development in the then High tech and new water-cooled “M96” engine developed for the 996. The intermediate shaft has long been a feature of the horizontally-opposed (also known as a “boxer” configuration) flat-six engines for which the Porsche 911 is so famous for, as long as the 911 has existed. Up to this point in the long lifetime of the evolution of the 911, the placement of an intermediate shaft on Porsche’s flat-sixes, in both concept and practice, had been tried and successful for years. With the advent of the M96 and the early production runs of the later-revised “M97″ engines, the failure is in the sealed cartridge-style ball-bearings that support the IMS.
The main weaknesses to the factory-original IMS bearings can be attributed to three reasons: 1) The material the ball-bearings are constructed of, are not strong enough to withstand the physical and thermal loads exerted upon them, 2) the lubrication of the bearings is insufficient and, 3) The wrong oil is used on oil changes or not changed soon enough.
There are many reasons for IMS bearing failure and often it is a combination of causes that results in bearing failure. The exact rate of failure of these IMS bearings is hard to pinpoint with any certainty. Claims, especially those made by Internet”experts” or ones found in the Porsche forum threads about this topic, can vary greatly, however, reliable sources have reported the failure-rate of some of these original bearings to be estimated as high as an astonishing 10% after an average of just 90,000 miles. Since it has also been documented that some IMS bearings have failed after just 3,000 miles, while others still have lasted for 200,000 miles or more, the only safe conclusion that can be drawn is that all M96 and some M97 engines in Porsche 911’s (996 or 997), and all Boxsters (986/987) from 1997 through 2008, are at risk of suffering IMS bearing failure at any time, irrespective of mileage.
Once an intermediate shaft bearing fails, options quickly become few and expensive. The absolute best case scenario (and least likely) is if only the intermediate shaft and bearings needs to be replaced, and even that still involves a complete engine removal, inspection, and disassembly.
The IMS bearing for these engines went through multiple design revisions from 1999 – ’06, including both single- and dual-row bearing designs, without ever adequately resolving the issue. Eventually, the M96 and M97 engines were replaced by the “9A1″ engine, the first 911-bound engine to completely dispense with the intermediate shaft system altogether in favor of a system that drives the camshafts directly off the crankshaft. That’s excellent news if you bought a 911 from the 2009 model year or later which has the newer 9A1 engine, but what can you do if you own a 911 with an M96 or M97 engine to prevent IMS bearing failure? And what if you’re looking to buy a used 911, how can you protect yourself from falling prey to a failed IMS bearing?