Quote:
Originally Posted by PaulE
Ok I was ignoring the fact that the IMS is in the sump so that makes sense. Crank journal and big end rod bearings are what I was thinking of that need the constant feed of oil under pressure. While Porsche decided to go with the grease packed sealed bearing at the flywheel engine and there is no internal oil gallery there, I don't see why they couldn't have put in a galley and a journal bearing, it is right below the crankshaft's rear main bearing. They had no problem getting an oil galley to the journal bearing on the front of the IMS. PS, I am sick of the IMSB too, having had
a preemptively installed ceramic one fail and going through a rebuild!
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Paul,
It doesn`t make much sense to me to use a pressurized oil lubricated journal bearing in a place that`s overwhelmed with oil anyways. I`ve never seen anything like this in any engine. I think a ball or roller bearing is perfect for this application, just the original, the single-row in particular, is undersized for this job. The dual-row still lasts for over 100k miles, which is not that bad in a performance car. The larger, non-removable bearing that`s installed in the newer Boxsters lasts pretty long too, at least I`ve never heard of any of those failed, but feel free to chime in if anyone have heard about such a bearing that failed.
Ceramic hybrids are not really good for this application because they are made for constant high speed and high temperature, that`s not really typical for a shaft that spins in the sump in oil at lower speed than the crankshaft. What the IMS is exposed to is the intermittent radial impact coming from the camshafts and transmitted by the chains. As the ceramic ball is much harder than the hardened steel races, eventually the intermittent radial load will make the races wear prematurely.