Doing clutch, not touching IMS

So my clutch just went in my 01 C4 and I've decided to get a scan done to check the timing, have a good look at the IMS and see if its leaking, and if all looks good, I'm not touching it. I'll get the clutch fixed and leave well enough alone. I keep reading about all these owners that have replaced their IMS only to discover afterwards that the part they just pulled out was perfectly fine. This car is my daily. Is driven hard, daily. And runs and sounds great. Oil is clear, etc etc. So I'm actually not worried about it. Current mileage is 125,000km - and I have no service records on her. So no idea if its ever been changed.

Hmmm.....i must question your judgement. I could understand not replacing the ims when no other repairs are being done. But if you are already that far in, the additional labor will be minimal and you will only pay for what ever part you choose (unless you go with the solution). To me the risk simply isnt worth the reward. You could look at as why pay the additional. But on the other side - if it were to fail you could easily be looking at 15k or more to have a shop put an engine in it.

I totally hear you. But, unless like you said, I go with the Solution, a $2500 Cad part, then a new ims isn't a guarantee either. The LN option is $1000 and when I read the long IMS forum I keep seeing the same thing, "original IMS looked good". However, it doesn't come down to $$, but more perceived risk. My mechanic and I have seen many 996's and none have had a blown IMS, except one that had 25k on it and was literally driven by an old lady. So where I go with that is, if the scan is good, and it looks and sounds good, then I'm not worried. Everyone's experience of course will be different, so many will probably disagree with my judgement, and I get that, but from where I sit, there may be no issue. Tranny comes out tomorrow, so will see how everything looks.

Owning a 996 proves you are gambler by nature. I like the odds. Annual oil changes, get oil sample, watch cam deviation and drive the car. If she blows build a monster 4.0L This is my plan.

01's the most problematic year...I'd think twice about this if I where you. Also, knowing it's a wear item, now would be a good time to change it.

In most cases i agree with you. I too did my ims with an LN part. The original bearing i sent into to confirm my warranty was in perfect shape at 61,000 miles. But i disagree with the method of checking. Checking timing is not an indication of the health of the bearing. Timing can be perfect and the bearing fail tomorrow. Timing could be off and it be due to chain issues, tensioners, guides and numerous other issues. Telling the health of the bearing is only possible by removing it and disassembly which would be pointless. Obviously you could remive the cover plate and check for end play. But again, why go that far and not change a known failure part. please no i am not arguing. Just trying to help with all perspectives.

If I was in there on an 01, I would consider changing it. The reason? Because ball bearings age on every rotation. It's closer to end of life now. But I like your thinking. The only other thing would be to take the flange off and remove the grease shield on it.

I agree with you. The IMS issue has been over-exploited by companies selling outrageously expensive solutions which are temporary fix.

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annual oil changes? Good luck with that...

There is no way to properly inspect the ims without pulling it out completely . A visual from the flange cover off won�t tell you much thing is once it�s out it can�t be put back in . So it�s a change anyway . Its a wear item , that should be changed on a reasonable interval when it gets enough hours . Not a run to failure part . There are lots of components in aircraft that are treated like this , if we maintained aircraft with a run to failure standard , we�d have crashes daily even the cheap $200 pelican ims is better than hope and pray once you get enough hours on the bearing It�s intended to be swapped out with every clutch .

Mi two cents. If you want peace of mind go with the pelican you will be sure that you will be fine for another 30,000 miles or more and it�s under $200.00 Take this from someone that just got his engine blown at 133,000k not IMS related but already spent over $10,000,00 and keeps claiming.

Don’t be stupid, you have the same single row bearing, it’s not a matter of if, but when. The single row bearing in your car is the worst of the bunch.

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Well, in reality, the bearing is run to failure. It's a 100% failure rate. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ That's the great thing about owning a Porsche. Risk - accepted. Not what I would do, but understand the thinking. Get a full flow filter. Change oil often, and cut the filter each time. Do the oil analysis, and hope for the best.

You are a skip away from the IMS and do not want to change it? I have seen it happen to my friend and it cost him plenty money. Hey, it's your car, your chances, your money,

I've owned 2 996's. The first one, I drove on pins and needles. Constantly worried about the IMS, wondered which version of the bearing I had, questioned if the vague carfax notes were in relation to it, etc. It really stressed me out and ultimately I got rid of the car because of fear of what might happen. It was not an enjoyable first Porsche experience. The second one I purchased full knowing what I was in for. I swapped out the bearing with an LN version, new OEM clutch, AOS, RMS, Flywheel, Fluids etc. before even taking possession of the car and I can tell you with 100% certainty it has been a far more enjoyable ownership experience having piece of mind that I've taken every precaution to keep the car in the best shape possible. It's a might as well, while you're in there item. Just do it and move on. If you sell the car in the next few years it will pay for itself.

I do not understand this logic, you are right there on a part known to fail. Weather you feel the failure rate is 100%, or .00002% you are literally going to be right at it, why would you leave it there? If you weren't dropping the engine to do other work I would understand your thought, but ITS RIGHT THERE!

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Yeah. Every time I heard a "noise" I was wondering if this was the end. I put an IMS solution in last year, and now I don't worry.

I’d replace it, like others have mentioned. You could even replace it with an OE bearing and you’d be starting over with a new bearing that had zero wear.

I agree with you, OP. I wouldn't change it either. Several reasons why I wouldn't. -You daily drive it and drive it hard. -These engines can fail for many reasons. IMSB is just one of them. -Replacing the IMSB is expensive. No reason to put that kind of money into it.

It's an 01- so could be dual or single row. I'll find out shortly. If it turns out to be single, maybe I'll throw in the pelican. But if it's dual, and looks good. She stays.

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-Drives it hard is more of an argument to replace it. -Yes than can fail for many reasons but this is one so why risk it -It is expensive IF YOU ARE NOT ALREADY DOING THE CLUTCH, he mechanic will literally be looking at the IMS. So you wouldn't endure the added cost of basically the part only to possibly avoid cooking a 12k engine later? This makes ZERO sense to me.

Statistics appeared to point to a correlation between *not* driving it hard & IMSB failing, though. So Prelude Guy is correct in his argument. There's always a lot of what I call 'IMSB Terrorism' rampant online, while factually only a few % of Single Row IMSB's ever failed, even less on the Dual Row. It's treated on here as if it is a guaranteed part to fail while factual data doesn't back that up. Let's not forget it will always be in some parties' best interest to keep these fears alive instead of taking them away - some of the parts/fixes being sold are outrageously expensive for what they are. An OEM quality bearing shouldn't ever cost more than 100$ - I've done my research on that one. (I've logged >5k problem-free miles in the past 5 months on my 80$ off-the-shelf dual-row after the 600$ FVD kit grenaded). IMSB replacement also requires either tool purchase for 200$ (or if you're lucky, rental from a forum-member) or labor. I can totally understand OP's line of reasoning.

at the very least, toss in a single or dual row retrofit eliminate the biggest chunk of risk it's really pennies over the life of the car

There are a lot of things that can break on these cars - scoring, d-chunks, chainguides and chains, etc etc. If you did all the 'pennies over the life of the car' to things that haven't given signs of wear, you'd be out the entire value of your car before you know it. The retrofit is a 8-900$ part excluding tools as well, wouldn't exactly call that pennies on the dollar, and is only guaranteed for some 70k miles. His original bearing held out for the same amount already, so why should he upgrade over OEM quality or upgrade at all if his OEM bearing turns out a dual-row and looks fine upon inspection?

Name 20 failure modes that have resulted in Porsche being sued, and agreeing to a financial settlement costing millions of dollars, covering tens of thousands of cars. From that list, name at least one failure mode that can be resolved with a solution under $1000. If one wants to go cheap, resolved for under $200 and 5 hours of labor.

To be fair, OP said "But if it's dual, and looks good. She stays.", and that lawsuit covers only the single-row bearing.

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Note that this is exactly what you most hope for. Once an IMSB has started to fail, there's no assurance that replacing it will do better than postpone engine failure. My two cents: Given that access is already paid for, the value of your car will increase by the additional cost of the IMS Solution. You should install this and proceed to enjoy peace of mind and a full refund if & when you sell.

Ectually, the lawsuit covers all cars from 1/1/2001 though the end of 2005. I don't believe the settlement discusses the type of bearing installed. obviously, this car being a model year 2001 was within the period defined in the lawsuit. Not that there's anything anyone can do about it now, as the last of the remediation is long behind us. LN estimates a 10% premature failure rate. In terms of modern mechanical design targets, this is out of spec by about a factor of 10,000. (sixth sigma = 0.00034, but who's counting decimals anyway). So, in effect, this is Russian roulette - but with a 10 barrel revolver(if there is such an animal).

I felt the IMSB was all overblown BS, having previously owned a 996 purchased at 32k and sold at 47k miles, all on the original bearing no issues. My 2nd 996 had its bearing changed by the PO as a precaution before he collected it. He gave me the original clutch and bearing with the car. I decided to clean up the bearing and have it on my desk for fun. I was shocked when I cleaned it up that the bearing was every so slightly rough, then when you look really close up you can see the races are damaged. I was shocked to be honest. Maybe the bearing would have lasted another 50k miles. I doubt it, once bearings pick up they eventually fail. Yours maybe perfect, but honestly when you come to sell it, all everyone will ask is is the bearing has been replaced, when I sold my first one, that was all they wanted to know. 9 out of 10 are not interested to even see the car if its not done. And the 1 that will see the car will try and offer $3k less than ask. If I were you I would spend the few hundred $ extra now whilst you have the car apart, if nothing more than make the car easier to sell when your ready.

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I think the lawsuit was for a specific set of serial numbers within that date range, so the date alone isn't conclusive. I'm pretty sure the serial numbers affected are the cars with single row. There was a thread a few weeks ago where there was a link to lawsuit serial number list. To the OP, I would change the bearing. It's one thing to gamble when no other work is being done, but when you are in there, can't find a way for that to make sense. Not that you should care what I think, but all bearings wear over time so it's a good idea regardless.

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It doesn't make sense to you because you're looking at it from only one point of view. These engines are unique in that they are essentially ticking time bombs. If the IMSB was the only issue with these engines, I would agree with you 100%. That's clearly not the case though. That's why there are several points of view. Another valid point of view is why put any money into them and just roll the dice on your luck. The argument here is why spend a lot of money on an unreliable engine that still doesn't make it much more reliable. Valid argument. You think it's a good idea to spend ~$2k on an already unreliable engine. I can see where you're coming from. However, I can also easily find a large number of people who thinks it makes no sense to even buy a car that is so unreliable. Who is right? Both? I think so. Lots of points of views when it comes to these cars, all having some degree of validity, too. As for daily driving/running these cars hard, evidence points towards these examples as being affected least by failed IMSBs. Cars that sit parked and driven on rare occassions tend to fail more often. Plus, based on my research, the bearing experiences the most stress when the engine is idling, not while revving. Again, there's no right answer when it comes to preventative maintenance on these engines. Anything short of a full rebuild is a gamble. The OP impresses me because he's actually being objective in his decision.

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Again, great advice......if the IMSB was the ONLY issue with these engines. It's not! But what if his engine fails for another reason other than the IMSB before he sells? Still no peace of mind. No full refund!

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I feel like you're looking for lightning where there isn't any, since you know damn well why <2001 isn't covered in the lawsuit. It's precisely because those have dual rows. 2001 being a changeover year, where some are and some aren't single-row and it's impossible to just tell by build date, they decided to cover the entire year but even then differentiate between serial numbers. The 10% estimate is for single-rows, you know that, so I'm a bit surprised you're framing it as if both IMSB's have that rate. It's specifically mentioned that dual-row IMSB has <1% failure rate.

Whether or not it needs to be replaced or is a good idea, one thing that changing it has a HUGE impact on is resale. IMS is a known issue with these cars and buyers know it. The person I bought my C4 from had it for sale for 6 months at a fair price and a lot of people looked at it. He said every person asked about the IMS and numerous people walked away specifically because it had not been changed. I�d change it for that reason alone. You�ll get far more than the cost of the change out of the car at resale time.

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Prelude guy, where are you coming up with 2 grand???? HE WILL HAVE THE CLUTCH OUT, we are talking another few hundred. And the IMS is not the only issue but it is one, so why not eliminate it? And if he goes to sell he is for sure to get 2k less because it is not replaced. Listen, I think the IMS issue is over played, but that goes to the argument of everyone knows about it so good luck selling if its not done. No one asks about timing chain guides and cylinder score when you are selling, they ask one question "Is the IMS replaced?"

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I would highly agree with this statement. When i called the Porsche dealer to inquire about purchasing my car that was the first thing the salesman said "It has not had the IMS replaced.". I even laughed and asked if he was actually trying to sell the car. He said they have had people all over the nation call and they hang up as soon as the hear about it. I just negotiated replacing the IMS, Clutch and RMS for an additional 2k over the asking price. They had no issue with it and neither did I.

^^ Yep. I would agree with not changing a dual-row, or the later, larger single-row, but the small single-row one that was based on the lawsuit, now THAT one, I would change almost regardless of clutch and having the engine dropped. Now that the engine is dropped and apart, I would almost certainly change it out. You could argue that the OP is technically making the �right� decision, technically, based on risk/reward, since there�s a 9 out of 10 chance the bearing won�t fail, and if you apply poker math/strategy to the equation. However, the argument falls down when you look at the economically correct decision. For example, if one were to buy 100 cars and have 10 bearings that fail, at $20k apice for rebuild, we have $200k in repairs, versus $100k of cost to replace the IMS on all 100 cars. So, economically, it is an incorrect choice to not replace the IMS if it�s $1000. Break even is $2,000, but that seems too steep.

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I'm not framing it either way. The OP doesn't know which bearing he has, but if it's a dual row he has decided not to R&R. I consider that an unacceptable risk, for the reason you gave. If the failure rate is less than 1% it is surely greater than 0.00034% by a factor of several thousand(3.4x10^4 to be exact). If one wants to live with a ~1% failure rate, where the cost of failure is $20,000, and the cost of remediation is $600-$1000, it's ok with me. I'm a numbers guy. I had a 99 with a perfect dual row bearing. But - numbers don't lie. 1% failure rate is way, way, way higher than I was willing to risk, particularly when I'm standing under the car, STARING at the IMS cover with the trans sitting on the floor. Have a nice day.

Not concerned at all.. not one bit. In fact let me start a thread explaining just how unconcerned I am😹

Could write a weekly newsletter based on everyone's IMSB opinions. Do the clutch and don't change the IMS, could have an issue down the road, might not and all will be fine. Do the clutch and change the IMS, one less potential worry and is now a buyers incentive if you decide to sell the car. Either way, it's how much the cost of the risk is worth to you and what you plan for the future. Have the extra money laying around and want extra peace of mind while accessible since doing the clutch? Cool do it. Not worried about it and want to drive the car as is? Cool do it. The world is your oyster.

And then you read stories of people removing perfectly fine dual row bearings and having the LN unit fail.

Wow, pretty emotional topic. My car is at a shop a stone's throw away from the thread starter. I'm getting the IMS Solution ++++++ on a 45000 mile car. Why? I am very risk averse and am trying to mitigate blowing a motor from a bad bearing design. I wish I was not as risk averse ad I am. In some ways I applaud the thread starter for his approach. Me, I was influenced by all the IMS failure lore and am paying $$$$$ dearly for it. Only time will tell who made the best decision.

One thing to bear in mind is that the 1% (dual-row) / 8% (single-row) statistic from the lawsuit is a data "snapshot" from a long time ago. All 996's are a lot older and they all have a lot more miles than they did back then, so the current failure percentage rate (for an original bearing at least) is probably quite a bit higher than it was back then. If the IMS has been changed at some point, then maybe 1%/8% is still roughly accurate, but if a car is still on the original bearing, the failure rate is probably quite a bit higher.

Well here are my 5 cents. I am kind in the same boat than the thread starter. I have an invoice of almost 3000$ onmy car at San Diego Porsche, where they changed the clutch, the RMS (with the new good 997 reference), IMS Flange/Housing, seal rings, cylinder hed seals etc. However, it seems that they didnt change the bearing itself (at least not with a porsche part). Why?... well it would take to the end of the days kind of discussion to define what is better, if an original bearing mounted from the factory with the engine that has no signs of failure, or an aftermarket one... I have to say though, that since I live here in US, I have realized that the view about the IMS "problem" is quite different from the one that we have in Europe. Although in both sides of the Atlantic the IMS is a point of concern with engines, I think that here we freak out a little bit more. Short story... in EU, if a 996 has been well cared (frequent oil changes, quality oil, driving respecting warming up times, etc)... and has not failed until today, you even consider them like quite reliable cars, and the proof is that you can see 996 with high millage without any service on the IMS.

Engine blows, sell as a roller and look for another cheap 996...Wash and repeat!

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I don't see how that is a debate at all. For most parts, I agree that aftermarket versus original is definitely a debate -- and OEM almost always win for typical mundane parts. For the IMS, however, the factory IMS bearings (at least some of them) have proven to be vulnerable. I guess for cheap aftermarket IMS bearings that are knockoffs of the original, then quality could be a question. However, the high quality IMS aftermarket options were specifically designed to be more robust than the OEM bearing. Whether they succeeded in that can be debated I guess, but the typical derogatory implication of "aftermarket" does not (in my opinion) really apply at all to quality third party IMS bearings. Even if those OEM bearings that made it to high mileage were actually manufactured better than the bearings that failed, all bearings are a wear item and all of the original bearings are getting long in the tooth both in terms of age and mileage.

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Well, I'd argue that even some of those bearing-replacement 'solutions' while more robust, carry an additional risk as they run un-sealed and are prone to total failure when *any* debris shows up in the oil. So any other wear-item going in the slightest and creating light metallic debris, would make these bearings almost certainly fail and with that the entire engine - they sit in unfiltered oil after all. So such bearings really only last as long as the next metallic wear part in the engine and needs to be replaced when some other benign engine part goes, as the bearing manufacturer himself states you cannot ever use them in an engine that ever had debris-laden oil. Then there are the 'aftermarket' parts that really did zero homework but just shipped overpriced boxes, like FVD Brombacher who ship 600$ kits with a wrongly spec'd bearing (wrong sealing) that actually accelerate the original failure path. Regarding 'cheap knockoffs', an OEM quality dual-row wouldn't cost more than 80$ - yes you read that right. That's a top-spec bearing from one of the big reputable bearing-manufacturers, that spec it to the same standards as Porsche did with the original ones. If you want to shell out more, you could even get some with improvements over OEM by ordering Viton seals - really, the seals were the only weakness of the OEM bearings. They're not expensive parts and there's little rocket-science left, all big manufacturers (SKF, SMT, ***) know very well what they're doing. But they're sold to Porsche owners, so they can be sold expensive.

I changed mine when I did the clutch and flywheel . My car was ten years old , only had 35k miles on it and I had receipts showing the oil had been changed in May and October every year I went in because there was an issue with the dm flywheel . I changed the clutch because I was in there a clutch change covers 80% of the cost of an ims bearing change because it’s the same labour . The extra labour to do the ims when you are in that far is minor . Took me two hours more , a pro who isn’t doing it for the first time should take less a new pelican Oem style bearing which will reset the clock and easily outlast the clutch is 200 bucks . The l&n options start at 800 and there are roller bearing options in between . Not doing it while you are in there is false economy . I didn’t stretch to the solution but if I had a freshly rebuilt motor with nikkkies etc I would go that way . i chose the l& n bearing because it also upgrades the stud , which is the second point of failure in the ims after the bearing and races . The oem one has a thinner section that also can fail . The pelican one also upgrades the center stud but reuses the oem flange . The L&n one comes with an upgraded flange and seal

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^^^^^^^^^^^^ Good info!

If the engine is throwing enough debris to accelerate an unsealed bearing failure , its haveing the same effect on every other moving part in the engine . It shouldn't qualify for an ims bearing replacement , it's ready for a rebuild . no little plastic bearing seal is going to save that .

I disagree, since all moving parts receive filtered oil while the bearing rests in the sump. A scavenger pump throwing metal will give debris in the sump, destroying any un-sealed IMSB while the rest of the engine remains intact - except for your pistons mauling your valves when the IMS goes, that is.. Replacing just the pump when discovering debris is a lot cheaper than replacing the entire engine as a result of the IMSB deciding to end it.

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Totally agree. That is the line that I wanted to underline. I work for a OEM supplier, which also provides to the aftermarket. Of course, there are high quality aftermarket parts, as OEM parts. But, IMO, what is incorrect, is to assume that the OEM part, developed specifically for that application, from companies which huge R&D capabilities (I tend to believe that SKF is able to develop a bearing with the same quality than smaller aftermarket companies), mounted in the factory (with factory tools and processes)... has to fail yes or yes and is better to replace yes or yes.

I think of the IMS as somewhat cheap insurance, so I did mine with the clutch. However, money is money, and I hate the risk of something else failing the engine after putting money into other areas that were not the problem. Owning this car is a balancing act between cost and risk and sometimes taking the risk is necessary. That being said, I would probably change out the single row. The engine on my 99 was replaced in 2001 resulting in my car having a single row bearing. The bearing moved great when you spun it in your hand and made no noise, BUT if you turned it very slowly you could feel that it was not 100% perfect. It definitely was not going to be a lifetime part. I would do what you are comfortable with an ignore the noise.. My tech put it best when he first met me and I was nervous about he car. "Even professional swimmers have drowned." There are so many other variables that could fail that engine, and this is the same with any car. My 08 civic had catastrophic engine failure when it was new...

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That is the quid of the question for me. That statement will be true, if we had the 100% security that the OEM bearing is going to fail. And actually that seems to be the mindset. "I have to change it for peace of mind, because sooner or later it will fail"... that means... the failure rate of these engines is 100%... Is that true? But, do we have any technical reason to think that, changing a "healthy" OEM bearing for an aftermarket is better? or are we just messing with an engine that wont fail, introducing non OEM parts with a predefined lifetime? Just trying to see all points of view

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the standard oem filter is a partial bypass system , it won�t catch all the glitter . Your basic assumption is incorrect

Failure rate (I think) is 5% of 996s. Cost of repair when it fails is $15K-$20K. What you should spend to remove the risk is 5% of $20K, or $1,000. The cost of the new bearing (LN) and additional cost of installation should fall under $1,000. The math says you should do it.

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having worked in engineering for both airplane engines and heavy equipment I would say that in most arenas outside the automotive sector when it comes to maintainence engineering , critical components come with a service life . After x number of hours you change it to prevent catastrophic failure . The automotive sector has other engineering pressures , cost etc . Cars are disposable and depreciating assets . In our winery yesterday by coincidence , a couple pulled up in a new panamera as I was pouring wine the fellow mentioned he was the head of Porsche technical services for western Canada ( Vancouver is the second biggest market for Porsche�s in North America after LA) his job is to train Porsche technicians , prior to that he was in charge of quality and trouble shooting , if a dealer had a car they couldn�t fix they flew him in . Anyway we we ended up talking about the 996 long story short his take was the bearing was undersized for the application it should have had a service life designated doubling the reccomended maintainence time from 12 to 24k miles in 2003 made the problem much worse . He also stated that the dominant aftermarket bearings were an excellent and reliable product . He would use one himself . he trains dealer techs how to replace the bearing as part of the Porsche classic program

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Exactly. In the highest mileage thread a lot of people have changed it once they passed about 140,000 miles. What condition were those bearings in? Personally, I got my car for so cheap (early 98 build date) that I'm going to change items that I know are failing and if the engine blows I'll just drop in a new one myself. Maybe at that time I would consider the solution, but even the solution there was a guy's whose failed after about 5k miles, due to improper install by a certified tech.

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That is a point of view (totally understandable, and I can agree with it) But in the other hand is, what if you are doing one of those cars in the 95%, that would be reliable cars, less reliable because changing the oem bearing for an aftermarket solution with limited lifetime? Because, as I said, sometimes it is the impression that, the bearing will fail 100% sure but that is not the reality. The reality is that there are a lot more reliable engines than engines that will fail, and when we take the decision a factor frequently ignored is that, by changing the bearing you can be also messing with one of the 95% (or whatever number) reliable engines.

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I appreciate your adamancy in telling me I'm incorrect, but I'm afraid you are. The OEM filter is a full-flow filter by design, in no way or form designed as partial bypass. There is a bypass valve that is designed to open only if the filter medium is severely clogged. Under normal circumstances with a regularly changed filter in there, it does not open unless your spring or bypass valve is faulty.

All I can say is thank goodness for the IMS bearing failures and associated ridiculous hysteria. If it wasn't this way, they wouldn't be so inexpensive and I probably wouldn't own a 911 (actually two).

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So according to this, you mean that the IMS will fail 100% in all cars. Is that correct?

Roll the dice, pay the price. Pretty straight forward

The oil filter operates in partial bypass almost all the time the oil is below about 40F for multi-vis oils, and somewhat higher temps for single weight oils(which almost no one uses). 5 bar is ~ 73PSI, and the spring spec was changed along the production, but it seems that in the early cars, it's set at around 60PSI or approx 4 bar. There is relief spring/valve at the end of the circuit and the filter bypass must by design be below the relief pressure or the filter may be badly damaged. The differential pressure across the filter media has a limit, just guessing but around 2 bar or roughly 30PSI. Beyond that differential, the bypass will open. Of course, with dirty media, it will open more, and at a correspondingly higher oil temp. the LN full flow design has no spring for bypass, and the filter is different and will maintain integrity at a higher differential pressure drop.

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Yes and no. Yes, kinda like the failure rate of human beings to survive is also 100%, if enough time passes... No, kinds like some 996s that probably have 200,000 miles on the original IMSB. So if a human had had a known issue - let�s say a heart issue that runs in the family where a pacemaker could extend life, would we risk it? Or would we take precautions? I can tell you, I�m the kind of guy who would visit the doctor and take precautions...others throw caution to the wind. And they could end up living to 115.

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When you say the "Solution" are you referring to the LN oil fed Bearing?

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Can you provide a source on those numbers, I assume someone must have measured the pressure differential at those temps then? I'd be happy to read those. Or have you done any calculations on this taking into account the filter area and permeability for 0WXX multigrade-oils at that temp? That makes little sense, as you said yourself that the bypass valve assembly is rated at 5 bar or at least 4 bar. With 2 bar across the filter medium, of course the bypass valve would not open in the slightest. Bar extraordinary circumstances like a clogged filter or extreme cold (I'm sceptical about the 40F number), the filter design is full-flow just like the LN setup.

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So, what we do prefer? A car that can runs over its original IMSB more than 200.000 miles? Or the same car where you have to change the aftermarket IMSB every 50K miles?

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it's a time curve , the more hours on the part the greater the chance of failure , other factors such as infrequent oil changes also increase the risk of failure . given enough hours , the risk of failure can be several orders of magnitude higher than the standard risk parameters. Theoretically given enough hours the bearing will fail 100% of the time , however in reality it's possible something else may go first when the engine accumulates huge hours The engineering principle behind service hour maintainence is to replace the items with a known failure rate at a concervative frequency . one thing to consider is that unless you are the original owner , you don't know if miles driven is an accurate measurement of the time the engine has been in operation . for example car A has 60k miles on it , it was used for road trips , long highways and rarely sat in rush hour traffic jams . Car B has 60k miles but was used for commuting 5 days a week , 10 miles each way and averaged 1.5 hours of time sitting in traffic idling but not accumulating miles . The engine in Car B could have as much as 3x the operating hours on it as Car A despite having the identical mileage .

This is not really an argument and beyond the point parris tries to make, since this assumes the rest of the engine lasts forever. Any part of any machine in the entire world - if used indefinitely - will fail at some point. This tells us nothing. Clearly what parris means with this percentage is the percentage of engines that fail as a result of IMSB failure before anything else in the engine. Plenty engines fail for other reasons - d-chunks, scoring and just general wear causing catastrophic failure. He's referring to the percentage where the bearing calls it quits before the 'normal' engine end-of-life. In what percentage of engines is the IMSB the first thing to go? 100%?

Quotes source post: 15443792

Yea I read about it here. Like 7 posts down. http://pedrosboard.com/read.php?7,26540,26540

Quotes source post: 15443659

one of the most common upgrades to the 996 is to convert to a full flow filter to eliminate the bypass . the oem bypass doesn't just open if the filter is plugged , it also opens under conditions such as cold temperature start ups ( I�ve actually driven a 996 @ minus 40�c in northern Alberta) and possibly high pressure use such as race track conditions . Cold starts would be the most common bypass scenario i stand by my statement that if there is enough swarf in your oil to eat up the open bearing , there is enough metal to cause major problems elseware . an engine with this level of metal flowing around isn't a candidate for ims replacement , it's on borrowed time until failure

Quotes source post: 15443926

what I'm saying is that if you are already into the job of a clutch change , which is 90% of the Labour cost of an ims change . Given the ims bearings known risk of failure , even installing a cheaper option such as the pelican bearing , which will give you a zero hour part of the same quality as the oem one and an upgraded center bolt , reducing the risk of 3 known failure points (bearings, race & bolt) , is worth doing . The higher the hours on the engine , the more this makes sense There are other pricier options for further reducing of the risk , improved bearings/ designs , but even this lower cost option is a sound engineering/ maintainence call . going all the way in to the clutch and not doing it ? I'm an engineer , hope and pray has never been part of my descision tree . others may take a more emotional or gut feel approach . its your car , a free country and you have enough information to make a descision .do what you like .

Quotes source post: 15443816

I did all my research when I changed the bearing and the oil filter housing. If you don't like the numbers, you are free to ignore it. In fact, it would be useful to put me on permanent ignore from your user CP. Assume whatever you like, it's a semi-free country.

Quotes source posts: 15443947, 15443978

'High pressure' use such as race-track conditions causing the bypass valve to open is nonsense, there's a pressure regulator valve inside your engine that prevents pre-filter oil pressure from ever going above 5 bar, regardless of RPM. During cold starts the bypass might open during extreme ambient cold only - I'm waiting on docmirror for source of his temperature values. You're free to have your opinion, but factually the oil system is designed with a full-flow oil filter setup. Calling it a partial-bypass filter is categorically false, unfortunately. The bypass is a safety feature which only opens during extreme beyond-spec circumstances such as extreme cold or a clogged filter. Certainly not on operating temps or during racing. The LN filter modification eliminates the risk of a faulty bypass valve, however leaves your engine at risk of oil starvation when operated outside normal operating specs, such as extremely low temperature start-ups or a clogged filter. Under normal operating circumstances, the bearing sits in unfiltered sump-oil while the rest of the engine (all critical pressurized parts) gets 100% filtered oil. If I have offended you with my inquiry, then I apologize? I'm only asking you to share your research (not just the results) which I don't think is unfair to ask.

Quotes source post: 15444016

You can't offend me. I'm just offering solutions here. It's the internet, I try to help. Some don't agree with me, and I'm really ok with that. When I see posts with "IMSB terrorism" it makes me chuckle, cuz it's the kind of head-in-sand, see no evil philosophy that presents when someone comes on here every week with another sob story about grinding noise and 'what should I dooooooooooooooo?'.

Quotes source post: 15444031

Alright, well if you're not willing to back up or defend your claims then I respect your choice.

Wonder how much time is spent beating this dead horse? That time could have been spent working to afford the maintenance item or... doing it themselves!

Quotes source post: 15443970

I see your point Vancouver (although the argument of saying that with time, the IMSB will fail, can be applied to any other part, or to almost any other engine). What I want to underline, is that, even when you hare doing the clutch, if the car has a healthy engine with a healthy IMSB, there is no technical data that justify that an aftermarket bearing is going to last more than the existing one. I have never seen nobody that can ensure that. If we are saying that the rate of failure is 5% (whatever) we are also saying that there are a lot of engines that will not fail under normal conditions and It is not crazy neither to think that somebody can prefer an original engine assembled from factory that one messed up on an indy workshop with an aftermarket bearing

Imagine being an indy mechanic and explaining to 1 in 10 clutch repairs that yeah, we could have saved you 10-15K and easily installed a bearing, but I read on a forum, " there is no technical data that justify that an aftermarket bearing is going to last more than the existing one. I have never seen nobody that can ensure that." Cuz, you know, forum threads are basically scientic research.

Quotes source post: 15444219

Huh?

Quotes source post: 15444219

Let's put that in a bit more nuanced perspective, as again the frame being set is that "the engine will most certainly fail without this part replaced". Honestly it's more like being an indy mechanic and explaining to your customer "for 200$ I'll sell you insurance that this particular engine part doesn't fail for 25.000 miles. 850$ and I'll sell you 75.000 miles insurance for this particular part not failing but only if the rest of your engine is absolutely pristine and not worn - can't offer the insurance otherwise. However, for 2000$ the insurance for this part not failing is unlimited miles. But without it, there's <1% chance your dual row bearing will fail for the life of the engine." Of course, to each their own decision, but the probabilities of failure are being overstated by use of subjective arguments. And all this is coming from someone (me) who had and IMSB failure in his own 996, ironic isn't it?

So the OP isn't the only person who changes a clutch and leaves the original IMS. I am looking at a 2001 Boxster as a cheap money toy so I asked the guy if he replaced the IMS (ad says he just replaced the clutch this summer) and his response was, "No the mechanic looked at it and said it was fine." I would like to know what they are actually looking at, its a sealed unit correct? So if they do not see oil leakage they assume its ok? Car is dirt cheap so I am not concerned too much about it, just was thinking, wow there is more than one person who would actually change the clutch and not the bearing on these things????

Quotes source post: 15444323

Did a bunch of work on GF's '01 Boxster (clutch included) this summer. Found a factory double row bearing. I had a Pelican on hand to replace a single row. Decided not to replace the factory double row with a new single row. Pulled the bearing seal, replaced the cover seal, and moved on.

Quotes source post: 15444219

It isn't really "aftermarket versus existing", it's " new versus old " on a part that is unquestionably a wear item. Nobody is obligated to put in an aftermarket bearing, everyone can pick whatever bearing they think is best. If you think the original bearing type is best, you can buy a Porsche bearing (I assume Porsche still sells them). Or you can buy an aftermarket bearing. The only reason aftermarket bearings like LN's are much more commonly used than Porsche replacement bearings is because of the perception (right or wrong) that the specialty aftermarket bearings are more robust. An old bearing, no matter how great it was when new, will still wear over time with usage. Safe harbor statements apply (past performance is not necessarily an indicator of future results).

It's getting pretty clear that aside from Vancouver and I, few if any know or understand the Weibull distribution and functions. sigh,,, doesn't stop anyone from posting here, which is all good. "Yup, I saw a bearing. Looked good, so we boxed it up, and went to Starbucks for a latte".[sic]

Harbor Freight should start selling an IMSB iteration.

For single row, I would argue strongly that you should always change it "while you are in there". For double row, I very much understand the debate, but "wear items" wear, so I still think it's a no brainer to change it as insurance while you are in there. To think that the new bearing will be worse than an old "magic" bearing that had no issues I don't think that is a valid concern, at least in the general case. Hopefully all quality new bearings are at least as good, quality-wise, as the factory original IMS. I don't know if this is the case, but it seems like all bearing manufacturers would have learned from past issues so that their new bearings are more robust than the original bearings. Hindsight should be 20/20, but again I have no idea if they actually did improve bearings based on past failures.

Quotes source posts: 15444354, 15444373

The thing is Porsche never sold it and still doesn't sell it as a replacement part. If there was a reasonably priced OEM Porsche bearing for sale, the argument of just slapping a new identical one in there would be a lot stronger. With aftermarket solutions, you've still got the unknowns of how well these aftermarket suppliers did their homework and how long this replacement bearing would last. Nice argumentum ad authoritatem you've got there. Fallacies don't bring much to the table in terms of pleasant discussion, but are amusing nonetheless. Though it almost seems hostile, I'm not sure where that's coming from?

Quotes source post: 15444411

Interesting. How did Porsche get away with not selling a replacement part? Seems indefensible in general and even more so for a critical part with a relatively high failure rate.

Quotes source post: 15444418

They basically said "The bearing cannot be serviced, if you want to replace it you have to buy an entire intermediate shaft" - for which replacement requires the engine case to be split apart. For cars covered under the lawsuit I guess this is exactly what they did, install entirely new shafts / replacement engines. For some reason they just never supplied the bearing itself.

If you're ever planning on selling the car, just replace it. The cost now will pay for itself in lack of headaches from tire kickers down the road.

Porsche has started selling bearings as part of the Porsche classic program , my understanding is you can get it done at one of these classic centers but they won't just sell the parts there was a whole thread on this a while back Raby said something about Porsche adopting the L&n method and tools they developed

Quotes source post: 15444480

good point.

From everything I’ve read, the new shaft makes perfect sense and is consistent with whyI would never replace the original bearing in a higher mileage car with anything other than a oil fed plain bearing. If it’s not broke, don’t fix it!! Yes, it’s not broke. It’s not on its way to being broke. We’ve heard stories of cars having the bearing replaced only to have the new bearing fail...but wait..the car wasn’t properly certified for a replacement! I think that certification came after the fact on the early replacements. So now it seems, you only replace the bearing on cars where the probability is exceptionally low to fail in the first place. Makes no sense to me. If the shaft is properly specced, I don’t think you need to replace the bearing. If your shaft isn’t in spec, then either a new roller bearing isn’t going to help or your car has probably already died if you have miles on it. i.e. the shaft is real problem. The original bearing would have been fine with a properly aligned shaft. Small deviations in the shaft put too much stress on original bearing design. That’s my take away on a nauseating amount of internet yammering. To each his own. By the way, IIRC, when Porsche settled the suit, they only agreed to a ten year window for compensation. It was already ten years when they settled so Porsche pretty much knew their liability already. Another cockeyed result where the company gets away with very little to pay, owners get the shaft( no shaft actually but a good pun) and the lawyers take their fees. Edit: I do agree if you are going to sell the car at some point it is easier to replace the bearing than listening to a bunch of tire kickers whine and waste your time.

Great information in this thread. Somehow the more I learn on this topic, the less I feel I know

But how can you sleep at night knowing about the dreaded...chain pad tensioners!?!

Quotes source post: 15444636

Don�t fret, soon you will be an internet expert, as qualified as most commenting on the IMSB - jumping on on these threads arguing fervently one point of view or the other.

Quotes source post: 15445078

Honestly those are what bother me more than anything because you see the little tiny bits of them with every oil change. It's like the tick-tock sound of the gator from Peter Pan.

LOL I might swap a Mezger in for the OP so nobody's feelings get hurt OP and I will be assessing and making the best move for him, it's not a cost driven experiment.

Quotes source post: 15445096

Sadly, I've already argued somewhat fervently in this thread . I've owned 2 996's, the first a 2001 back when they were new, so I did not even know what IMS was (good times, good times). My second 2000 996 had it's dual-row IMS replaced at 62k miles, I plan to replace it again at the 112k (50k intervals). Nothing I've read changes that plan, but it's always good to be informed, so I find these threads very beneficial.

I had mine pulled by an excellent SoCal indy shop at 60K miles after reading all the tales of horror and grief concerning my 2000 C2. The existing single row bearing - inspected closely once pulled - appeared to be in absolutely perfect condition. For what it's worth.

If you think about it, wouldn�t any IMSB that�s pulled out should look like it�s perfect or like new? Isn�t that how it�s supposed to look?

Quotes source post: 15438000

OP, it�s been several days since this post. We�re all anxious to know what you decided. Updates?

Quotes source post: 15447346

Bingo! That’s my understanding. Certified installers would reject a bearing retrofit when the old bearing is beyond Stage 1. Unfortunately, from what Ive heard and read, many shops don’t care and install a new bearing in a contaminated engine even when they can see the old bearing is shedding metal. No skin off their backs. Blame it on LN, blame it on EPS, blame it on Pelican parts, blame it on Porsche, but it’s not our fault!!

Quotes source post: 15447360

That's only a real issue for LN's (and EPS's?) bearings though, since they're open and sit in unfiltered oil. Sealed bearings such as Pelican parts can be fitted without a problem if the removed bearing wasn't immaculate.

Quotes source post: 15447369

LN Engineering RetroFit bearings are sealed. Notice in attached video. Also, doesn�t LN manufacture Pelican�s IMS retrofit bearing? You Tube

That is not a sealed bearing, though. There's some sort of shield that I think gave you the wrong impression. LNE's hybrid ceramic bearings are splash-oil lubricated with unfiltered sump oil. The rear is sealed (inside the IMS shaft so it doesn't fill with oil), the front is not.

Not sure I wanna even go here, but I'll play devil's advocate. If an LN, or any other aftermarket bearing is supposed to only go into an pristine engine, how can we ever tell if that bearing is better than the original? Aren't we switching out a perfectly good bearing that hasn't failed, and may never fail for an "upgraded" one that will also not fail if it goes into a motor that is not shedding debris? Full disclosure, my 99 has an LN double row, done 20K miles ago. Original bearing was in great shape.

Quotes source post: 15447593

Thanks for clarifying. It looks like some sort of seal. And, this makes more sense... LN recommends removing the front seal on m97 large bearings. My 996 has low miles and when they removed the flange, the grease seal was compromised- pulling away from the edges. The shaft was filled with oil too. What is your take on this? You think a sealed bearing is a better idea?

Quotes source post: 15447593

That is correct. What you see is the cage (ball separator). The bearing is indeed open and lubricated with engine oil from the sump. If there is debris in the engine, the bearing, as well as other engine components, will be compromised. That's the importance of the pre-qual to make sure that the engine is in good enough shape to be retrofitted. This includes dropping the sump among other items. It's worth the few extra hours of labor before you start a job to find out that you have a healthy engine rather than spending thousands to just have a cylinder fail a few months later, which we see more often than people would like to admit.

Quotes source post: 15447653

My personal take on stock bearings is that if the seal is failing and you're not replacing it, you might as well remove the seal - the path to failure is oil getting in there and losing its ability to lubricate as it never gets refreshed. Removing the seal - while adding risk of foreign object debris damage - allows old oil out and fresh oil in such that it's at least lubricated. Whether or not I'd remove the seal if it isn't leaking yet, I'm not sure. Porsche put a sealed bearing in for a reason, and I think that reason is that the oil it sits in is unfiltered. My personal vehicle had metal shavings from a IMSB failure so I had to go with a sealed off-the-shelf bearing. It's been happy for six months now / 5000 miles.

[Image-only post; no author-written text. Original image references:] https://cimg2.ibsrv.net/gimg/rennlist.com-vbulletin/2000x1124/ims_e2e6fb887481c70f906a0fb92b30f210397d36ba.jpg https://rennlist.com/forums/graemlins/thumbup.gif

Quotes source post: 15449846

Squeaky clean! Cleaned up nice. What car is this? Care to share?

Quotes source post: 15449858

this is the OP's 2001 C4, initial clean-up

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Super! He hasn't posted on the thread in quite a while. What decision was made about the IMS bearing?

Did I miss dirty before shots?

Quotes source posts: 15449907, 15449909

If it was mine the IMS would not be replaced. Double row.... waiting on his decision oh she was dirty

Quotes source post: 15449939

Wow, I'm surprise. Since you mentioned the Mezger before, I would have thought you'd recommend the plain bearing design of the IMS Solution.

Thanks for posting the pics 993GT! So the motor and tranny are our of the car, and as you can see from the pic, clean dual row. It will stay, I won't lose any sleep. Car will be getting new clutch kit including flywheel, RMS, AOS, some coolant lines, water pump, thermo, belts, maybe a sensor or two. Then she will be good for another 100,000 km. I live on a dirt road, and the AOS had a bit of a leak, so she was dirty. Not anymore.

Someone asked for the before shot? Just dropped.

Where are you having this done?

Quotes source post: 15449939

Curious if you would not personally replace it because: A. You think it is not necessary (given condition of current IMS) OR B. You think there is more risk in replacing the original with an aftermarket sealed bearing (that is the same design as the original bearing).

Quotes source post: 15447917

As a frugal mechanic of more than 40 years, I agree with these statements. On a new engine that sheds a lot of break-in debris, a sealed bearing would be ideal over a non-sealed bearing. On an engine that has had a bearing shedding debris also a sealed bearing would be nessesary. Once the debris production has stopped, either from break-in or repair/replacement of cause, the filtering system must catch all the debris, then a non-sealed bearing would be more reliable due to more dependable lubrication. The filtering system on the m96 is not much basically different from a conventional engine (other than the by-pass location in the bottom of the canister), but the drain back of spent oil in quite different in that there is not a direct flow of drain back, so debris can linger and hide for a lot longer before being captured by the filtering system. I've seen many engines have a failure of a new camshaft/lifter (especially on a new high/lift non-roller cam conventional engines), and debris laden oil. Replacement of the failed components and a flush and a few frequent oil changes have sucessfully repaired them. The ones which were not sucessfull are3 the ones that fail slowly, with debris that is small enough to pass through the filter and remain suspended in the oil that is not changed for many miles. This will damage the main and rod bearings and would even damage a "IMS Solution" as it is primarily a plane bearings just like the main and rod bearings with the same lubricating oil. Anything that will damage the main or rod bearing, will also damage the "IMS Solution". For me personally, the decisions are based in economics along with probability.Being in the middle class (lower middle class) and having 3 cars with m96 engines, the Solution while being my first choice, would cost about 6k to equip all 3 cars, I could buy another 986. To me the greatest contribution to the m96 from Flat6 was the idea of replacing the IMS bearing with the engine still in the car. This was revolutionary ! As before the only factory procedure was to completly remove, dissemble, clean engine, and replace the IMS shaft. I was under the impression that the Flat6/LN retrofit was intended as a repair to keep from having to do a complete tear down/ rebuild of the engine in instances of a IMSB failure. While it is obvious with the pre-qualifiing procedure now implemented,that it is not to used for failure repair,only preventative maintenance, I'm not sure if it was originally. As far as economics go, if you are faced with an IMSB failure and decide to do as Boxman did and replace the IMSB with a sealed bearing and flush the engine and do a few frequent oil changes, the only thing you really risk is damage to the main/rod bearing and crankshaft. Since main and rod bearing would normally in replaced during a rebuild, the added cost of the crankshaft damage would be only risk(1k). So if you decide not to take a chance and rebuild with new cylinders/pistons, bearings, rebuild heads, chains, guides, gaskets, seals ect, you have spent 15k, or take the risk and spend 16k after the bearings fail( or maybe all the debris is captured and no failure occures) I would never condemn any one from over maintaining/servicing or repairing their car, as an enthusiast there is no such thing and I'm often jealous of anyone who can do it. As a recap. The best choice in my opinion if you got the cash in the "Solution". The ceramic/hybrid or non-sealed bearing is best choice for a well broken-in and pristine engine. A new engine or one that has had anything producing debris, a sealed bearing would be best untill the production or lingering debris is captured.

Peterp - its both. A and B

Quotes source post: 15450506

Holdfast, I completely respect your position on the subject. I hope you get lots of years out of the engine. Please report back good or bad. rock on!!!

Quotes source post: 15449939

How can you tell if is a single or a double row bearing.

Visual inspection once you remove the flange.

Quotes source post: 15450715

Can you tell by this picture?

^that's a single row

Quotes source post: 15450734

I was thinking the same thing but this is a picture of a 2002 3.6 and I was under the impression this was only put on the 3.4 engines

Quotes source post: 15450772

post '99 3.4 (00/01) it could be either style and are unknown til you see it. 3.6 cars were all single row to my knowledge with 997 2005.5+ engines getting the large OD single bearing