The IMS (intermediate shaft) problem is fascinating. These discussions have been going on for years because of the major consequences of its failure. OEM ball bearings have steel balls, steel races (the inner and outer collars), a steel cage to maintain proper spacing between ball bearings, and dual plastic seals on both sides of the bearing with grease packing.
Ball bearings can fail because of the following (taken in part from
Ball Bearing Lubrication in Centrifugal Pumps | Maintenance World – An article source for maintenance management and equipment reliability professionals
A. Contamination of the bearing oil or grease by water moisture or foreign particles. As little as 0.002% water in the bearing oil will reduce bearing life 48%.
B. High heat caused by too much lubrication. With to much lubrication the bearing will consume energy as it plows through the lubricant. This energy will show up as heat added to the lubricant causing it to first lose its viscosity and then the lubricant will begin to form varnish and coke (i.e. solids) as it gets hotter. The recommended oil level should be half way through the bottom ball when the pump is at rest. The problem with grease and oil lubricants is their low specific heat and their poor conductivity. It is for this reason that it is not recommend to put any type of oil between dual seals if it can be avoided.
C. Of course, too little lubrication will cause failure.
D. If loads are too massive, the bearing will crushed, bent, etc. immediately.
My limited observation of the failure of ball bearings is that the steel cage is a critical component of catastrophic ball bearing failure. As the friction becomes too large either because of poor lubrication, too much lubrication, or contamination by foreign objects, the steel cage stops rotating properly with the steel balls. Once the cage starts to lose its integrity friction increases even more leading to total disintegration of the cage. This results in the two steel races and ball bearings remain pretty much intact (although damaged), however the cage disintegrates into pieces. Because the balls are no longer properly spaced within the inner and outer races, the two races separate leading to catastrophic failure of the bearing. In IMS failures the debris is carried throughout the engine causing even more damage.
Regarding the IMS bearings in Porsches, it appears that the following are generally agreed upon.
1. The early double row ball bearing (up to about MY2000) in the M96 engine has a very low, but real, failure rate (maybe <1%).
2. The first small single row ball bearing (MY2001-2005) in the M96 engine has the highest failure rate (about 8%), and is the smallest of the three ball bearings.
3. The second larger single row ball bearing (MY2006-2008) in the M97 engine has a low failure rate to date (about 1%).
4. The bearing load capacity of the double row and second larger single row bearing is about twice that of the first small single row bearing (see bristol,
http://forums.pelicanparts.com/boxster-cayman-forum/757877-direct-oil-injection-7.html
5. The oil level in the IMS bearing with the engine off and the car level is about 25% up from the bottom of the bearing, and is nearly ideal (see feelyx,
http://forums.pelicanparts.com/boxster-cayman-forum/757877-direct-oil-injection-8.html). Once the engine is running, the oil level must fall, probably below the IMS bearing altogether.
6. Track driven cars appear to have fewer failures than “garage queen” cars that are driven more gently. Track driven cars are also likely to have modified sumps allowing for storage of more engine oil.
7. Removal of the outer seal of the IMS bearing probably improves bearing life (see LN Engineering or Flat 6 Innovation websites). It is unclear if removal of both seals would be beneficial.
8. IMS ceramic bearings use ceramic balls with steel inner and outer rings. While the ceramic material itself is stronger than steel, it is also stiffer, which results in increased stresses on the rings, and hence decreased load capacity. However, they can be more effective in environments where lubrication is less than ideal (see
Ball bearing - Wikipedia, the free encyclopedia).
9. The seals were never expected to keep the original grease in the bearing and the oil out. Seals can keep the dirt out and the grease in when the operating environment is air, but the seals could never be expected to keep engine oil out when the bottom 25% of the bearing is submerged in oil. Consequently, it is inconceivable to believe that Porsche engineers would expect the IMS bearing to be lubricated by grease.
The following is one way to integrate these findings (none of these are new thoughts but they are all in one place). Obviously, the ball bearing application in the IMS of Porsche engines is flawed, with the double bearing and second larger bearing being able to withstand more deterioration before failure compared to the first small bearing used in MY2001-2005. A completely submerged ball bearing would also fail from the increased resistance due to too much lubrication whether or not both seals were in place or removed. If the bottom part of the bearing was always in oil, then it would be properly lubricated probably regardless if both seals were present or not. However, the IMS bearing is only in oil before the engine is started. Once the engine is running the oil level in the sump decreases and no longer submerges any part of the bearing, and the presence of both seals will make any splash lubrication even more problematic. Consequently, removing the outer seal will allow for some improvement in lubrication. An engine that is raced or tracked will be constantly accelerating and decelerating, thereby splashing the sump oil upward toward the IMS bearing compared to a “garage queen” car that is driven gently. The recommendation by LN Engineering to replace the small single ceramic bearing every 50,000 miles suggests that splash lubrication is too marginal even for a ceramic bearing to be dependable. This suggests that all types of IMS ball bearings require improved lubrication.
The Tuners Motorsport (Pedro’s TechnoFix) Direct Oil Feed (DOF) has the possibility of properly lubricating the IMS bearing under the following conditions: (1) There is not too much oil fed to the bearing. It appears that the port in the IMS flange was altered last year to supply less oil (about 400cc/min from 1,400cc/min -see forums). Hopefully, 400cc/min will not be found to be too much lubrication. (2) That the oil is clear of debris particles that could otherwise become trapped in the bearing. It is possible that the bearing could act somewhat as a filter, and with the high flow of oil from the DOF the bearing may have an increased probability of being damaged by debris. In comparison, because the volume of oil due to splash lubrication would be smaller, there may be a smaller probability of debris damaging the bearing. Consequently, using only well filtered oil is probably critical. (3) Because the DOF appears to apply the oil at right angles to the bearing, hopefully the axial force of the oil hitting the bearing gage will not cause it to deform or wear improperly. A spray of oil may be better than a stream of oil. The IMS Solution (
Home) also uses DOF but to a new IMS bearing that is not a ball bearing.
So the obvious question is: Why did the Porsche engineers design the IMS bearing used in the water cooled engines until 2009. Apparently, they could no longer use plain bearings that were pressure fed at both ends of the IMS in the newer water cooled engines, in contrast to the old aircooled engines. Consequently, Porsche decided upon a ball bearing at one end, and initially it seemed to work in engines with the double row ball bearing. Because there were too few IMS failures with this engine, Porsche did not recognize the ball bearing actually was a critical weak point. However, by the second design with the small single row IMS bearing, the problem became readily apparent. Consequently, they had enough time to alter the engine design to incorporate a larger single bearing in the M97 engine, but they needed more time to design and deploy the next generation of engines that did not use an IMS (in 2009). And Porsche was not going to stop selling cars just because of an intermittent, catastrophic engine problem.
Why then, did the engineers continue to have the IMS bearing installed with both seals? The most likely answer is that they thought the bearing received enough lubrication particularly since the bearing was submerged 25% in oil with the engine off. And by keeping the seals in place, any oil in the bearing may be kept inside the bearing. In addition, they probably thought that the presence of both seals was important in keeping debris out of the bearing. However, we now know that the presence of both seals keeps lubrication out while the engine is running, and this becomes a more important factor than keeping debris out. Lastly, the corporate side of Porsche decided it would cost less to the company to deal with engine failures on an individual basis, and perhaps also on a class-action basis then to order a recall to solve the IMS problem in all of their engines.