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An intermediate shaft has been used ever since Porsche developed the aircooled 911 engine,

starting in 1965 with the 2.0. The purpose of the intermediate shaft is to drive the camshafts

indirectly off the crankshaft. By using an intermediate shaft, the speed of the chains are reduced,

which is better for chain life. This basic design was used throughout the entire lifespan of the

aircooled six-cylinder Mezger engine used through 1998. The inclusion of an intermediate shaft

which drives the camshafts indirectly off the crankshaft has been a mainstay of the

horizontally-opposed flat 6 engine utilized by Porsche.

The same design has been retained with the water-cooled Turbo, GT2, and GT3 models as their

engines are based off the same 964 engine case with the same internals as the earlier aircooled

engines. This intermediate shaft features plain bearings that are pressure fed engine oil for

lubrication and never fail. If these bearings wear out, and engine may develop a slight knocking

noise due to increased running clearance, but this condition will never result in a catastrophic engine failure.

With the introduction of the Boxster in 1997, a sealed ball bearing was used on the flywheel side of the engine to support the intermediate shaft rather than a pressure fed, plain bearing, like the one used on the opposite end that is fed oil directly from the oil pump. Porsche did not provide a procedure or specify a service interval for the original bearing. All Boxster, Cayman, and 911 models from 1997 through 1998 share this design, with exception of the Turbo, GT2, and GT3 models that utilize the Mezger engine. To learn more about the intermediate shaft, check out IMS 101.


Fact 1. The M96 and M97 Engine is wet sump - the IMS is submerged in oil. No forced oiling or direct oil feed is required for any ball or roller bearing when an open bearing is used.

Fact 2. Ceramic hybrid ball bearings only need 1cc of oil per minute and chosen by Porsche in 2017 for their IMS bearing replacement, almost a decade after introduction of the IMS Retrofit.

Fact 3. The dual row bearings used in the Patented Single Row Pro and Classic Dual Row IMS Retrofit have load ratings equal to similarly sized cylindrical roller ims bearings.

Fact 4. A ball bearing was originally chosen by Porsche because of its ability to handle both axial and thrust loads evenly.

Fact 5. The IMS Solution is the only permanent fix that backdates your IMS to work like the IMS in an aircooled Mezger flat 6 engine.

Fact 6. With over 30,000 sold and installed since 2008, the IMS Retrofit and IMS Solution are trusted worldwide as the first and best ims replacement option.

Fact 7. To date, there are no confirmed failures of the dual row bearings used in the Single Row Pro or Classic Dual Row IMS Retrofit kits or of the IMS Solution.


From 1997 to 1999, Porsche use a dual row intermediate shaft bearing which has proven to be as robust as the larger single row used from 2006 through 2008 model years. The Eisen vs Porsche Class Action Lawsuit filed against Porsche over IMS failures revealed the factory Dual Row was much stronger than the Single Row used from 2000-2005. According to information published about the Eisen IMS Class Action Lawsuit, the single row IMS bearing used in 2000 through 2005 model years is reported to have an 8% failure rate, versus less than 1% with the dual row IMS bearing which has twice the load capacity of the single row bearing used by Porsche.

Starting in 2000, Porsche began phasing out the dual row bearing and went to a smaller single row, with significantly less load capacity. From 2002 through 2005, all engines used this smaller intermediate shaft bearing until they went to the larger, third revision for the 2006 model year, which increased the load capacity back to what the original dual row bearing could support. The larger model year 2006 and later bearing also increased the diameter, which increased the bearing and ball speed, further improving the bearing. However, this change has not been enough to resolve the IMS failure issues completely.

If your engine was replaced in or after model year 2006, it will have the larger non-serviceable bearing even if that bearing wasn't original to your model year. Replacement engines from Porsche utilized whatever was the most current IMS bearing in the year the engine was build.

By far, the single row ball-bearing used starting in model year 2000 through 2005 are the most problematic. With half the load capacity, it is clear to see that the reduced load capacity of the single row IMS bearing is a significant contributing factor to the increased number of failures and that oiling alone is not the cause or solution to IMS issues.


Although most 2005 model year Boxster and 911 vehicles will have engines originally fitted with the problematic 6204 single row ball bearing, some late builds will have received the larger, non-serviceable 6305 series ball bearing. Even though the larger 06-08 intermediate shaft bearing is the most robust bearing Porsche used from the factory, we recommend that you still plan on having the grease seal removed off the IMS bearing to extend the life of the original bearing as soon as possible. This allows the bearing to be lubricated by the oil in the sump. This bit of preventative maintenance is important since the engine must be completely disassembled to replace the bearing. And yes, before you ask, we are aware of a company that recommends boring out the case to allow you to change the bearing. We strongly encourage anyone who is thinking of having this invasive procedure done ask yourself, where does all that foreign object debris go - into the engine. In the process, you will compromise the entire engine. Just do yourself a favor and have the grease seal removed. This can be very simply done once the IMS flange is removed. The following video shows you how to remove the grease seal. Once you pull the seal, you can replace the IMS flange seals and o-ring on the center stud. Just be sure to follow the required IMS servicing procedure before carrying out any work.

Once the seal has been removed, we recommend a shorter oil change interval of no more than 6 months and 5,000 miles, using a quality 5w40 motor oil. Regular used oil analysis along with periodic inspection of the oil filter can be used to monitor the condition of the IMS bearing moving forward.





Many people do not know, but Porsche chose to use a ceramic bearing for their replacement IMS kit released in 2017, which uses a sealed 6204 ceramic hybrid bearing, with 52100 steel races and sintered silicon nitride balls. This comes a full decade after LN Engineering publicly released its first IMS Retrofit kit, using the same bearing technology Porsche eventually chose to utilize with their own bearing replacement.



Ceramic hybrid ball bearings use 52100 steel races with sintered silicon nitride (ceramic) balls. In the case of the IMS Retrofit, CERBEC balls are utilized.

52100 bearing steel is one kind of special steel with features of high wear resistance and rolling fatigue strength. High-carbon chromium bearing steel, engineering steel and some types of stainless steel and heat resistant steel are used as materials of bearings and for other purposes.

Sintered silicon nitride balls are used in ceramic hybrid ball bearings. There are many benefits to these advanced ceramics over conventional steel balls, including no cold welding or adhesive wear, and with lowered centrifugal forces, ball-skidding is minimized. Beyond spalling caused by mechanical overload which is commonly seen in original IMS bearings, adhesive wear and ball-skidding are commonly seen in worn or failing IMS bearings.

Silicon nitride is a chemical compound of the elements silicon and nitrogen. Si3N4 is the most thermodynamically stable of the silicon nitrides. It was not until the 1970s that manufacturing costs were reduced and the sintering process, which takes a slurry and under extreme temperature and pressure, allows shapes, like ceramic ball bearings, to be manufactured. The resulting material is highly resistant to abrasion and corrosion, with the highest fracture resistance of all ceramics used in manufacturing. Beyond engine, wheel, transmission, and clutch bearings, silicon nitride components have found their way into motorsports, medical, aircraft, and manufacturing. Specifically, it can be used in valve trains, rotors and stators in turbines, turbochargers, and even rockets, where few materials exist that can survive extreme conditions.

Naysayers cite conventional bearings, whether roller or ball bearing, as a better choice for the IMS than a ceramic hybrid ball bearing, but those studies carried out by NASA are over 14 years old. Early ceramics did indeed have a shorter service life than bearings with conventional balls, but modern ceramic hybrid bearings with sintered silicon nitride balls have been proven to last anywhere from three to ten times longer, exceeding predicted life significantly, suggesting models for bearing life do not accurately match real world results of ceramic hybrid ball bearings.

Since their introduction in the 1960s and development carried out by SKF (MRC) in the 1970s, ceramics have improved greatly, eliminating concerns about reliability, with cost being their only limiting factor in implementation in applications where their wear resistance and reduced friction promote longer bearing life compared to conventional bearings. The first commercially available ceramic bearings were offered in 1984 and it was Koyo that pioneered the first practical application of silicon nitride in bearings. It is believed that automobile manufacturers will continue to utilizing silicon nitride as greater demands for increased fuel economy are mandated.


Oiling is just one part of the problem. The solution is simple. The intermediate shaft is located at the bottom of the engine and is submerged in oil. Eliminating the grease seal opens up the bearing to the oil located in the “integrated dry sump,” aka wet sump where all the oil is housed. As supplied by Porsche, the intermediate shaft uses a sealed ball bearing. The original bearing was grease filled, considered a “permanent” lubricant. However, the original bearings and seals used are rated only to 250F and over time, the seals become hard, allowing the grease under normal operation to be “washed” out of the bearing during operation. As the intermediate shaft itself is completely submerged at times, the shaft will actually fill up with engine oil. With long drain intervals, contaminants in the oil find their way into the bearings and intermediate shaft. The IMS tube itself will end up storing a sizable amount of oil that will centrifugally be fed to the bearing during operation. This is another reason why frequent oil changes are a must – as this oil gets trapped and is one of the sources for lubrication of the bearing! These worn out seals do allow oil in but they also limit the exchange of fresh oil in and out of the intermediate shaft.

Once the bearing begins to wear, the seal will actually fail completely, allowing for oil to wash out the permanent grease but not allowing for fresh oil to exchange in and out of the bearing during operation. It is at this point that you can begin to find debris in the filter from the seal and from the bearing itself.

The IMS Retrofit uses an open bearing (no grease seal), allow engine oil to freely enter and exit the bearing. The ceramic hybrid bearing used in all IMS Retrofit kits require minimal oiling, far exceeded by oil in the engine’s “integrated dry sump.” According to, a higher oil level, especially in higher speed applications, often creates more heat. This can reduce the oil viscosity even further, leading to metal-to-metal contact in the bearing, and a reduction in bearing service life. The proper static oil level for an open single row deep groove ball bearing mounted on a horizontal shaft is at the centerline of the lowest rolling element.

Some claim without forced oiling of the ball bearing there is inadequate lubrication. Unfortunately, there is no evidence of this with thousands of stock or ceramic hybrid replacement bearings we have inspected. If oil alone was the problem, we would expect failure percentages from the Eisen Class Action Lawsuit to be the same for single and dual row IMS bearings, which is clearly not the case.

Another issue that forced oiling of a ball bearing does not solve is over-loading of the ball bearing.
The single row ball bearing used starting in 2000 through 2005 was replaced with a larger bearing in 2006 with double the load capacity, restoring the original load capacity the dual row bearing first used in the M96 engine. Insufficient load capacity leading to wear and fatigue is the primary problem with the single row bearing used in 2000 through 2005, not lubrication! It is for this same reason that the class action lawsuit settlement regarding the IMS only covers vehicles with the single row bearing as found in 2000 through 2005 model year vehicles!

The IMS Solution and Single Row Pro IMS Retrofit both provide increased load capacity over the conventional single row bearing, but the IMS Solution eliminates the problematic ball bearing by using a simple plain bearing that is pressure fed oil. Orifice size as well as oil source for lubrication of the IMS Solution has been engineered to ensure optimal operation while not causing side-effects from pressure losses (leading to lifter and variocam problems), oil foaming, and crankcase windage that flood oil feeding a ball bearing causes.

Forced oiling of the ball bearing does not provide any benefit as the bearing does not require or benefit from additional oil. Lubrication alone is not the problem.


As you would imagine, the IMS Retrofit kit went through many iterations during development, including forced oiling of the ball bearing prior to switching to a ceramic ball for it’s performance in environments with poor lubrication. We did develop a version that utilized a cylindrical roller bearing with thrust ring, but it never made it from testing to production for the primary reason that Porsche chose a ball bearing originally, not a roller. Remember that Porsche also chose to use a ceramic hybrid ball bearing for their replacement released in 2017 as well when they could have chosen a roller bearing. Roller bearings have been used in automotive applications like gearboxes when paired with a ball bearing for thrust control for many years and can also be utilized in this application if sufficient thrust control is provided. Some manufacturers make false claims about the load ratings of their roller bearings with deceptive advertising. So when researching what bearing technology you want to use, there are some facts that are important to consider:

A deep groove ball bearing as currently used in the IMS Retrofit can take up to 50% of the dynamic load in thrust.

A traditional cylindrical roller bearing with thrust control can only take up to 10% of the dynamic load in thrust.

Roller bearings are higher friction than ball bearings.

The factory single row 6204 bearing a dynamic load capacity of 2900# with thrust max load rating of 1450#.

The NJ or NU204 cylindrical bearing commonly used in IMS bearing replacements has a dynamic load capacity of 3750# with thrust max load rating of 375#.

The custom dual row ceramic hybrid ball bearings used in both the Single Row Pro and Classic Dual Row IMS Retrofit has a dynamic load capacity of 4000# w/ Thrust or 2000#.


SSF Imported Auto Parts specifically requested a roller bearing kit to satisfy requests from the independent Porsche repair shops they service as they were not satisfied by any of the commercially available roller bearing kits offered by other suppliers. LN Engineering was able to supply them an already proven design superior to all other cylindrical roller bearing IMS kits. The expanded load capacity roller bearing utilized in the RND RS Roller cylindrical roller bearing IMS kit has a 5800# dynamic load capacity with thrust 580#, without any requirement for additional forced lubrication. Typical installations of cylindrical roller bearings are paired with a ball bearing to provide thrust control, where the RND RS Roller has integrated thrust control internal to the bearing. For those unfamiliar with SSF Auto Parts, they are a wholesale distributor of quality European auto parts and supply repair shops as well as parts retailers such as Pelican Parts. You may have done business with SSF and not even known it. Click here to learn more about SSF.


Roller bearings, like ball bearings, will have service intervals, requiring future replacement. The only IMS replacement that is permanent and does not require future servicing is the IMS Solution.


For some, choosing to roll the dice and hope they do not experience a failure is the right thing to do. Odds are in your favor that you’ll never experience a failure. That is little consolation for those having experience a failure out of warranty. Others choose to purchase extended warranties or have some sort of preventative or proactive maintenance done to protect their investment. First and foremost, owners should continue to drive and enjoy their cars and not let fear dictate their actions or inactions. Being informed and aware is the first step to happy Porsche ownership.

It is not known exactly why these bearings failure, but there are many contributing factors including over-loading. Poor lubrication, long drain intervals, high fuel and moisture content in the engine oil, high oil temperatures, and even operational speeds can affect bearing life. That’s why some bearings last 3,000 miles and others have lasted over 200,000 miles. One thing is for sure. Once you have experienced an IMS bearing failure, there is no turning back. A complete engine disassembly is required to replace the intermediate shaft and in most cases, complete rebuild or engine replacement is your only option.

When an IMS failure occurs, or more specifically the ball-bearing or bearing support fails, the intermediate shaft is damaged beyond the point of being serviceable, but moreover, debris from the failure contaminates the entire engine, requiring a complete teardown and rebuild to recover from such a failure. In worst-case scenarios, the cam timing can also be thrown off, causing valve to piston contact, and in some cases, even lead to a failure that requires replacement of the engine. In that case, the engine will not be accepted as a core, requiring the purchase of another core or to pay an ever-increasing core charge on top of the cost of the replacement engine. Aside from the pro-active approach of replacing the IMS bearing prior to such a failure, prevention and early detection are some of the steps that can be taken to try to minimize the risk of a costly engine failure.

One attempt at extending the life of the original IMS bearing removing the grease seal off the factory intermediate shaft bearings for years to better improve their lubrication and cooling, as is the case with model year 2006 through 2008 engines, as that’s the only preventative measure that can be taken that is cost effective as the other option is to tear down the engine completely to access the intermediate shaft, for which upgraded IMS bearings are available for installation at this point.

With model year 1997 through 2005 engines however, the bearing is indeed accessible. Any IMS bearing replacement is intended to be installed as a pro-active measure in preventative and regular maintenance. Once an engine has suffered a failure, replacement of the intermediate shaft bearing is no longer an option. Installing a replacement IMS bearing in an engine that has already suffered a failure will result in a subsequent failure due to collateral damage, including but not limited to debris contaminating the new bearing.


Remember, not driving your car or worst yet, not driving it like Porsche intended can make the problem worse. Although a greatly debated subject, most experts agree that more frequent oil changes every 6 months or 5,000 miles is a good first step. Secondly, actually driving your Porsche more often and avoiding higher gears to keep the revs above 2500-3000 rpm is another good step to take to improve the life of the ball-bearing in the intermediate shaft. Although there is limited data, the general trend is that lower mileage vehicles with infrequent oil changes or driven light-footed (as in run at low speed/engine rpms) are most likely to suffer a failure rather than those cars that are driven hard and well-maintained. Along with more frequent oil changes, the addition of a magnetic drain plug coupled with close inspection of the oil filter and magnet at these shorter intervals may help owners identify a failure in its early stages, but later models using the single row bearing can fail with little warning. When inspecting the filter and magnetic drain plug, ferromagnetic debris from the intermediate shaft bearing can be identified easily, appearing like silver glitter. Larger debris than this is indicative of a complete failure. Installation of the LN Engineering Spin-On Filter Adapter can help to prevent debris from re-entering the engine. This is accomplished by eliminating the bypass that can allow this wear metal from causing collateral damage in your engine. When using the Spin on Filter Adapter & FilterMag, a filter cutter is used to inspect the full flow filter.


The IMS Retrofit and IMS Solution procedures are intended for PROACTIVE installation and not REACTIVE measures only and should be considered a preventative maintenance item, like a timing belt on many modern engines. Once your original bearing has failed it is too late. Performing an IMS Retrofit or IMS Solution procedure after a failure will not “save” your engine. By no means should an IMS Retrofit procedure be carried out if the original bearing has started to fail as the intermediate shaft will be damaged by such failure. If the IMS bearing needs to be cut out of the IMS bearing tube (shaft) to remove it, by no means can a new bearing be installed! The engine will have to be disassembled and intermediate shaft replaced.


There are many reasons for bearing failure, and usually each failure is due to a combination of causes, not just a single cause. Spalling occurs as a result of normal fatigue where the bearing has reached the end of its normal life span but this is not the most common cause of bearing failure. Spalling detected in bearings can generally be attributed to other factors. A common cause of bearing failure is due to contamination from tiny metallic particles left over from a previous mechanical failure. These particles are suspended in the oil and if they are allowed to get into the bearing, the result is tiny dents in the hard steel raceway. Often the dent is surrounded by a microscopic raised area (or ‘lip’), and when the ball rolls over this lip, the ultra-high point loading exceeds the strength of the steel and it fractures, leaving behind a jagged depression (or ‘pit’). Once this cycle begins, wear is greatly accelerated and the bearing will fail prematurely. One of the most common sources of trouble in bearings is wear and pitting caused by foreign particles and is responsible for 70% of all early bearing failures.



The following eleven step IMS Retrofit Pre- Qualification procedure was developed by Jake Raby at Flat 6 Innovations. During the initial development of the IMS Retrofit Procedure and components, some items of concern were noted from the very beginning. Over the years, these procedures have been updated to address these, thus increasing the effectiveness of the IMS Retrofit procedure. This procedure has been employed at Flat 6 Innovations since the very first IMS Retrofit was performed. To date it has resulted in a 100% success rate for the Flat 6 Innovations Preventative Service program. Having performed the very first IMS Retrofit and after performing more IMS Retrofits than any other facility, a perfect record has been maintained by Flat 6 Innovations by employing these procedures verbatim. Today, roughly 20% of all engines that are inspected will fail this pre- qualification, and will require repairs to be made prior to the IMS Retrofit being performed. The biggest mistake that can be made is assuming that every vehicle is healthy enough to have the IMS Retrofit performed. The second biggest mistake that can be made is not taking the pre-qualification procedure seriously. Please, pay attention to each and every engine, and realize that not every engine is a viable candidate for an IMS Retrofit.




On 1997 through 2005 models where the IMS bearing is serviceable, excluding parts bearing replacement usually takes 10 to 14 hours and depends on the model being serviced. Tiptronic 911 models require the engine and transmission to be dropped to facilitate replacement of the IMS bearing, so plan on extra expense with those models. Boxster, Cayman, and 911 vehicles from model year 2006 through 2008 have a non-serviceable IMS bearing which should have the grease seal removed to allow the engine oil to properly lubricate the bearing.




Vehicles previously retrofitted with an IMS Retrofit or IMS Solution IMS bearing replacement should have a serial number sticker affixed. LN Engineering maintains an online database. You can look up your IMS serial number at which provides production date and if registered, will also provide additional information regarding the installation (where available).


The Single Row Pro and Classic Dual Row IMS Retrofit are offered with a two year or 24,000 miles limited warranty, whichever comes first. The IMS Solution carries a five year unlimited mileage limited warranty. The warranty is valid only if the product was installed as part of preventative maintenance before the original bearing failed or has begun to fail and all installation guidelines and requirements including pre-qualification and registration are met.


Depending on which bearing is used, the recommended service interval varies by time and mileage, whichever comes first:

Classic Single Row IMS Retrofit (which was superseded by the Single Row Pro) - 4 years or 50,000 miles.
Single Row Pro and Classic Dual Row IMS Retrofit - 6 years or 75,000 miles.
The IMS Solution - Permanent. Designed for the life of the engine.




The IMS Retrofit™ and IMS Solution™ are registered trademarks of LN Engineering LLC - the original ceramic hybrid ball-bearing and only permanent oil-fed plain bearing replacement for the M96 / M97 engine - the only IMS kits trusted by hundreds of independent mechanics and used by dealerships worldwide. All other bearing replacements are just imitations.

All genuine LN IMS Retrofit kits come laser etched, engraved, and serial numbered to validate their authenticity and feature custom-made, ceramic hybrid ball bearings made exclusively for LN Engineering using Japanese 52100 bearing races, polyamide or steel cages, and genuine Cerbec sintered silicon nitride ceramic balls that are made in the USA.



Prevent costly engine failure by eliminating the problematic ball-bearing by backdating your IMS with a pressure fed oil lubricated plain bearing, just like in an aircooled Porsche. This patented design is the last IMS bearing you will ever need.




Cylindrical bearings provide great lateral load capacity, sacrificing their maximum load cap in thrust (axial movement). That’s why precise thrust control is crucial for bearing’s longevity and reliability. RND Roller Bearing IMS Retrofit kit is the only cylindrical roller bearing IMS fix on the market that uses a Genuine Koyo bearing featuring proper heat treated, 52100 bearing steel thrust surfaces on both sides to handle thrust load both fore and aft with increased number of roller elements for added load capacity. Manufactured by RND Engines for distribution by Pelican Parts (Retail) and SSF Imported Auto Parts (Wholesale).


The IMS Guardian was manufactured by Flat 6 Innovations. Replacement MCD drain plugs are available from Flat 6 Innovations.

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