Quote:
Originally Posted by thom4782
Can you ask a more specific question? The following will clarify why I am asking.
It seems to me that the bearing is under load so long as the engine drive chains are moving. I would think the substantive issue is just how much load does the bearing bear under different operating conditions. The hypothesis I am about to advance is pure educated guessing on my part.
My theory is that forces create load - centripetal due to rotation and vibrational. At constant RPM, the bearing experiences some degree of load, say X. As acceleration increases RPMs, I think the loading increases as the chains increase rotational speed of engine components. At higher RPMs, however, the vibrational loading component decreases because vibrational amplitudes don't have time to reach their full heights.
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I am not clear on the vibration part. Is that vibration of the IM shaft, or the bearing components.
Here is some information I found that touches on rpm and lubrication-
"
The engineer’s initial thoughts were that the ball-separator failure led to bearing collapse, but after analysis of said IMS bearings, it would appear that bearing wear/fatigue spalls lead to separator wear and outer race failure. Separator failure and bearing collapse causes catastrophic failure of the mounting bolt(s) and IMS/timing chain components. The first recommendation was to use a bearing without seals and secondly to use a higher viscosity oil (with greater film strength). More frequent changes will also improve lubrication quality. An oil with extreme pressure additives like Moly might also further assist in increasing bearing life. Higher rpms also increases bearing life as this lessens the viscosity requirements of the lubricant to maintain EHD lubrication, also providing a reasonable explanation of the lack of IMS failures in tracked cars or those driven "like they were stolen." Likewise, far more failures are found in engines with low mileage that are garage queens and never driven to their full protential."
Source:
PORSCHE Intermediate shaft upgrade kit for PORSCHE BOXSTER ENGINE 986 AND PORSCHE 911 996 ENGINE
I have to admit I am stuck on rolling bearings for the IM shaft. I just keep asking myself why Porsche insisted on using a rolling bearing for so long. Was it because it was the best fit for handling dynamic forces that they were not able to engineer out of their production parts.