Another IMS bearing thread

[Walter White]

Originally Posted by Jake Raby

But Pedro's video shows centrifugal force throwing oil AWAY from the IMSB area? Not that I agree with that, but your hypothesis states the opposite.

The M96 bearings LOVE RPM because it helps unload them, the M97 bearings hate it because the components spin too fast. M96 bearings fail on the street, M97 bearings fail on the track and seldom on the street, very seldom. Load is the evil constant.

I am not familiar with the video you mentioned, but it would be nice if the oil would sling off the chains, but stick to the bearing.
When I was experimenting with getting oil to a bearing spinning at 4 - 6K RPMs, I was getting the idea that the bearing wasn't getting any oil at all. I would drop a drop of oil into the race of the spinning bearing and it would instantly vaporize. I don't think the oil ever even got to the contact surfaces.

[Jake Raby]

Originally Posted by Walter White

I am not familiar with the video you mentioned, but it would be nice if the oil would sling off the chains, but stick to the bearing.

He's posted it in several threads. In all your research I can't believe that you haven't found it.

[thom4782]

Originally Posted by Walter White

Is the bearing under load while accelerating?

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.

[Walter White]

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.

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.

[BudmanV24]

Originally Posted by Walter White

I am not familiar with the video you mentioned, but it would be nice if the oil would sling off the chains, but stick to the bearing.
When I was experimenting with getting oil to a bearing spinning at 4 - 6K RPMs, I was getting the idea that the bearing wasn't getting any oil at all. I would drop a drop of oil into the race of the spinning bearing and it would instantly vaporize. I don't think the oil ever even got to the contact surfaces.

At high rpms, ball bearings prefer an oil vapor. Take a look at ball bearing turbos, albeit at a much higher rpm, they fog the bearings.

[Jamesp]

Originally Posted by BudmanV24

At high rpms, ball bearings prefer an oil vapor. Take a look at ball bearing turbos, albeit at a much higher rpm, they fog the bearings.

Reading bearing manufacturer data on lubrication shows that high rpm requires lower viscosity (thinner) lubrication, and low RPM requires higher viscosity lubrication. It was explained that that the lubrication has to "be in the way" when needed, and also be able to "get out of the way" so the bearing elements can pass. This supports longer bearing life in aggressively driven cars that have engine oil in the bearing. So to the folks out there with 200K+ on their cars, we know how you drive.

[Steve Tinker]

Originally Posted by Jamesp

Reading bearing manufacturer data on lubrication shows that high rpm requires lower viscosity (thinner) lubrication, and low RPM requires higher viscosity lubrication. So to the folks out there with 200K+ on their cars, we know how you drive.

Or they drive at really low revs with really thick oil......

[Jake Raby]

Porsche used the ball bearing because it was the cheapest way to control radial and longitudinal loads. It killed two birds with one stone, and found them in a class action suit.

The dual row IMSB has TWO thrust control surfaces to assist with those longitudinal loads and that is a very welcome aspect of the dual row design. Two rows have proven to be better than one.