Quote:
Originally Posted by PaulE
I think a sealed ball bearIng packed with grease that is doomed to be washed away by the oil all around it was a half-assed idea at best. It’s like whoever designed the engine thought they were finished designing it, realized they forgot to deal with lubricating a bearing on the back end of the IMS and stuck the sealed bearing in there because it was too late to put an oil galley in the block to lubricate a tried and true plain journal bearing. At least LN and Flat Six studied the problem and came up with the open bearing with ceramic balls that should continue to function with splash lubrication. Nothing is always 100% perfect but they tried to improve on the design a lot of owners were already stuck with. Porsche’s ultimate answer was to eliminate the IMS entirely in their next generation of flat six engines.
Well that’s what I think, I’m not an engineer, but it’s my opinion.
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I agree with you on that it was a stupid idea in the first place to put a sealed grease-filled bearing onto one end of an air-sealed tube that allows for vacuum building up which forces the oil into the tube through the bearing. The other smart step by Porsche was to replace the dual-row bearing to a much weaker single-row that`s clearly undersized for this application. It`s just plain stupid. IMHO if they had stuck to the original dual row design with no seals (bc the IMS is literally swimming in oil and not lubricated by vapor or splash) the IMS failure would not exist. Like in the newer engines with the irreplacable bearing, which is larger (well-sized for the job) and works just fine with removed seals.
However, your example got me thinking and I `m tending to think the hybrid-ceramic is not the way to go either. (I know, your example is just n=1, but LN states none of their bearings ever failed, which is strange, because then why did the come up with another solution?). I`m saying this after I already put a hybrid-ceramic into my IMS... These bearings are best for high temperature, high rpms and minimal radial impact, like turbines. None of these conditions really stands in the crankcase. But, the IMS is exposed to a repetitive radial impact at high frequency due to opening the valves. Eventually due to this impact the ceramic balls that are much harder may wear the steel race prematurely. Interesting paper on the topic, just FYI:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050175860.pdf