[500_19B]

The M96 issues were thoroughly discussed in a famous Excellence article penned by Jim Pasha several years a ago. The various items that had been noted in the previous decade were discussed in detail, with much input and quotes from known experts such as Jake Raby. In addition to the known issues, it was also pointed out that the engines also have some great design features too.

Of all the issues, IMS is one of the only one that remains a mystery (the question of cylinder ovality in 3.4s as documented by Hartech being the other). Porous blocks and slipped sleeves are both issues pertaining to a very specific number of early cars and RMS has been dealt with quite effectively. Six or seven years ago, the forums were ablaze with the "dreaded" RMS, but now, not nearly so much.

The trouble with IMS is that there remains much mystery as to why some cars never have an issue and others do. Driving style, mainentenance etc. have all been hypothesized, but there is no clear cause and effect. Other than noting that good maintenance will never be a bad thing, where does that leave us?

In my view, where possible (i.e. early 2005 and earlier), I would treat the IMS bearing as a wear item and periodically replace it (like water pumps etc). As well, I wouild replace it with the LN Engineering bearing, as that is an upgrade. I just bought a 2004 Boxster S, and that is my plan. Going forward, I plan to regularly continue to replace the IMSB with the LN unit, perhaps on a three year/12,000 mile basis. Most would argue that this is an excessively short frequency, but that is my conservative choice. As pointed out, clutch, RMS and other things can be attended to at the same time and, done at a shop, it should be less than $3K easily, parts and labor. That is not cheap, but ammortized on an annual basis, not so bad IMO.

I truly beleive that if the IMS is dealt with in this way, that the rest of the M96 may be a great motor (cylinder ovalilty being the one other area I'd think about -especially for 3.4s). Obviously Porsche revised the IMSB design several times, and ultimately eliminated it with the 2009 9A1 motor.

The question is a little trickier if you have a late 2005 through to 2008 M97 motor, as for those, the IMSB can only be replaced after the case is split, which moves it from something that can be addressed as PM within reasonable cost to something much more expensive. However, those cars have the latest IMSB design, and although the numbers aren't there to know for sure, I expect those cars are least likely to suffer. If I had an M97, I would maintain it very well (of course) and perhaps consider an IMS Guardian as an warning device.

This is all written from a cautious, conservative point of view. Many people drive their M96s with no problems and never know what IMS is. I personally know of two Boxsters with over 200K miles (one with over 250K), none of which have had any major work. Howver, there are some (1%, 5%, whatever) who have the bad luck, and then it can be very expensive.