IMS Bearing, I'm a 99 Percenter

[maytag]

It makes sense if the failures are related to a production flaw, but not if they're due to a design flaw.
Hear me out:

If the failed IMS bearings were all from a certain oem supplier, or from a certain set of date codes, then one could have faith in the idea that "if it hasn't failed by xx miles, it won't". We could imagine that, nestled deep in the motor, is an IMS from a different OEM, or a different date code.

If, however, the failures are due to a design flaw, then the number of miles should serve to INCREASE likelihood of failure. (Because, as you say, the longer it's stressed, the more likely to fail)

To be honest, I don't know what to make of "no correlation to mileage", other than the frequency of failures must be so profoundly low as to be too small a sample to track trends.

??

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[Boxstard]

Originally Posted by MWS

I've heard the mileage failure rate nonsense for years and have always quickly dismissed it as it's just counterintuitive to common sense, or at least to my limited version of "common sense". I'd agree that low use cars (and bearings) are (or can be) subject to failure for many understandable reasons, but the logic of thinking "I've made it to xx,xxx mi without issue, so I don't need to worry about it" is just plain dumb. It's a bearing, under load and with friction...it will fail; and the longer the bearing is subjected to wear, the greater risk of failure.

To use an analogy...let's say that you purchased tires that you discovered had a known design failure and that you had heard that the failure *usually* happened under 1,000mi...if you continued to use such tires, would you think "I've made it to 50,000mi, I guess my tires are good" and continue to blissfully drive along? Of course not. Tires wear, and the wear is visable. Just because a component is buried deep and out of sight doesn't mean wear isn't slowly degrading the functionality and shortening the lifespan.

I can understand trying to find comfort and console in a belief to to mitigate fear, but those who wish to follow the "high mileage IMSB" preachers are *ahem* delusional. Please accept my most sincere apologies if I have offended, but please, don't just believe something because you want it to be true.

Of course, I am fully open to meaningful contradiction. My complete and total wrongness on any given subject only leads to a learning experience.

I won’t expect tires to last over 50K miles on my Boxster, not even close. But I do expect my original IMS bearing to last 100K miles or more by design, specifically the original dual row bearing.

Incidents with downgraded single row design exposed potential weakness in the system but I find some truth in someone suggesting less failure expected once past 50-75K miles for the double row. Early bearing failure may signify quality/ tolerance issues, but bearing life could be infinite when lubricated properly and loaded below its capacity, like many other components are originally designed for under ‘ideal’ conditions. Tires just wear out no matter what...

After all, this issue comes down to half glass full or empty... not a single answer for all. Personally I have no fear with my original double row bearing, just keep my oil fresh and full and drive the car the way it is meant to be, almost daily through the year and enjoy every second of it. I may think about it if my clutch needs replacement but good chance that I’d still leave it alone... it has ONLY 83K miles!

[Luckyman01]

I am the original poster, it was a dual row, likely did not need replacing however I have the piece of mind now. BTW, pulling that bearing was no small task, I destroyed 3 tools b4 success. That inner spring clip was a bear. A machinist friend took the challenge personally and fabbed a puller that worked.

[mikefocke]

Originally Posted by maytag

To be honest, I don't know what to make of "no correlation to mileage", other than the frequency of failures must be so profoundly low as to be too small a sample to track trends.

??

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There are so many variations and no central authority tracking things. Porsche didn't for a long time want to know for legal reasons and fixes were, until recently, not Porsche developed or approved. Nor could they know all as replacement engines were frequently third party installations from wrecks.

First there are production variations. How do the crankshaft and IMS mounting holes line up in the block. Then the parts variations, thing like the trueness of idler pully bearings and such. Then the randomness of manufacturing tolerances in the bearings themselves. Now throw in weather conditions, driver techniques, oils used, oil change frequency, etc.

I've seen postings of 10k failures and 350k non failures. Two on the same car. Every transmission. Everything else clean. Everything in the engine trashed.