IMS failures on automatics?

[BFeller]

Originally Posted by JFP in PA

One theory about the whole ball of wax was postulated by a rather serious Porsche after market engine builder with some serious credentials. He commented about the well known RMS leaking issue were very low mileage M96 engines started leaking oil badly, noting that Porsche released a special “go/no go” testing tool the measured the concentricity of the RMS opening in the case, which tested to see if the case opening was actually centered on the crank center line, and which found many were not. PCNA approved new engines for any that failed this test while under warranty, and released a new designed seal that was a lot more forgiving of misalignment. His theory was if the RMS case opening could be off center, was it possible that the IMS opening just above the RMS could also be misaligned. While the PTFE RMS seal could make up for misalignment, the metal on metal IMS flange had no hope of doing this, resulting in weird loading on the IMS bearing in engines with misalignment. The same engine builder also noted that when he spun up IMS shafts on a lathe before pinning the rear gear to prevent it from slipping (it is pressed on, and yes it too is a potential problem point), he noted that he found a lot of run out at the bearing opening on quite a few shafts, which he tossed out rather than reusing. So there is a whole bunch of possible reasons for problems to occur, which leads us back to the crap shoot description; get the wrong combination and you lose, big........... It also plays into another fact: the oil fed solid bearing IMS Solution is by its design much more tolerant of misalignment than either a ball bearing or roller bearing retrofit, which may explain why there has never been a reported failure of a retrofitted IMS Solution.

If you think about it, an engine with case opening misalignment and/or a wobbling shaft could explain why an engine that was pulled after failure and sent back to the factory for rebuild, could fail a second time; the true problem(s) were never repaired, just new parts installed. And it became a problem waiting for a new owner.

Thank you for posting this information.