peterp

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.

User 63031

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.

Vancouver996

peterp

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

Vancouver996

User 63031

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.

parris

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.

twitchett

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...

parris

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

Vancouver996

yelcab

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.

Vancouver996

bull3t

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.

parris

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.

User 63031

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.