Volkert

There was not too long ago a conversation on a IMSB failure AFTER replacing the bearing. This was a case 35.000km (20k miles?) after replacement. Fingers pointed to LN Engineering. I checked out the case and it appears this failure was with a none-ceramic single row bearing from LN. I remember these were available earlier? The car was driven regularily after replacement and had regular inspections and oil changes by a Porsche dealer. The engine will be taken apart further in coming weeks but until now all points to a bearing or shaft failure.

My point is that this is the biggest fear of many; spending the money or purchasing a car with IMSB done and then it fails. Can we collect some documented cases of such failures? I think we all are familiar with some of the 24 modes of failure of an M96 and I for one believe often fingers are pointed to IMSB failure while the actual failure mode is/could be another one. But still, if they do, why do they fail?

Charles Navarro

LN Engineering has never offered a non-ceramic hybrid IMS bearing. Sorry, but you must have another bearing in your engine.

dporto

Chris(MA)

If I recall correctly (might be wrong) that car had an undisclosed (disclosed later) rear end crash that could have damaged something in the engine, leading to eventually failure after some miles were put on.
Also it was not clear what actually caused the engine meltdown, too much overall damage to pinpoint the IMS as the fault.

Its worth bearing(sic) in mind that case and IM shaft runout is one of the factors at play with IMS fails. If the engine runout is bad, swapping to a better bearing won't fix that problem.

My car had 102k miles on the OEM IMS bearing and it was almost perfect, so my runout must be good.

The runout problem might be one of the reason Porsche on the 997 moved the IMS bearing location to the internal portion of the engine which made it inaccessible from the flywheel side. Perhaps they felt during manufacture they could control it better by machining from the reverse side?

Charles Navarro

I've carried out a runout survey and found huge variations in shafts. We check every shaft before pinning and replacing the bearings - anything over .005" runout we fail. The highest we've seen is .020".

The late 06-08 shafts have the most consistent bearing housing bores.

Schnell Gelb

Thank you Charles !
Honestly, how many of us who have diligently rebuilt an M96 had the runout/OOR etc measured? We did not have any specs to follow,had no procedure. We did not even hear the first mention of the issue until relatively recently in the decade+ long IMSB saga.
So thanks to LN for raising the issue. Very helpful.

Charles Navarro

Correction. Worst IMS had .028" of runout.

I uploaded a few of the photos from my analysis done a while back for those interested:

https://www.dropbox.com/sh/jysa8bfih...nSeD00yza?dl=0

Schnell Gelb

Wow ,so run-out measurement locations are :
1. the tube
2. the base of all the gears
3. the extreme end of the gear assy.
Interesting that an IMS tube with only 2 thou run-out can have a gear with 28 thou ! see photo #16 - if I am reading correctly?
How long would the bearing in that tube last? Yikes.

Charles Navarro

Hard to be sure how long a bad one would last - certainly don't want to try! Some of these shafts came in to us with wear or bearings in process of failing.

The way the IMS is made, there are a bunch of parts that are all swedged together onto a pipe without any key ways - just a press fit.

An example of dimensional stack-up at its finest.

Chris(MA)

Yikes.....

Volkert

Thanks Charles for the clarification. Luckily, it is not my car, mine is humming along nicely with a new clutch and a new ceramic LN dual row bearing installed by a competent mechanic using the right tools. Thanks for your work on this subject and your feedback in this thread.

To Chris (MA): no, this is a seperate instance.