13 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHAre there alternative causes for IMSB failure?
Reported or suspected cause
lot more complicated
Suggestion or failed attempt
No successful repair reported for this finding.
0
Identified cause
1
Suspected cause
0
Reported fixes
Read evidence and context
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Discussions that suspect a cause
1
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Suspected cause
Based on the maximum load calculation on wikipedia (granted the formula is probably a lot more complicated but I am no expert and I am just guesstimate the width and diameter of each bearing)
Leading evidence: 'lot more complicated' (no explicit attributable resolution; this is a reported action or suggestion). Across 1 matching discussions, the most frequently mentioned possible cause is 'lot more complicated' (1 discussions; 0 report identifying it and 1 suggest it). The most frequently discussed action is 'Check these claims' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Discussions that contain suggestions
1
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Suggestion · Original poster
I'm cross-checking these claims with the experience of the forums
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
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Suggestion
If an unsealed bearing is put into an engine that has had a failed bearing the new bearing doesn't have a chance unless the engine was stripped to bare cases and ultrasonically cleaned."
Explicit resolution reports before identified causes, performed actions and suggestions. Within each level, matching component labels precede direct query mentions and inherited thread context; successful versus unsuccessful discussion counts, owner confirmations and independent discussion support determine order. This is not a probability of success.
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Suggestion
Montly oil changes have solve this design problem.
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
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Suggestion
If an unsealed bearing is put into an engine that has had a failed bearing the new bearing doesn't have a chance unless the engine was stripped to bare cases and ultrasonically cleaned."
These are separate views of the same evidence. Frequency alone does not establish a fix, and these counts must not be added together.
lot more complicated
No successful repair reported for this finding.
0
Identified cause
1
Suspected cause
0
Reported fixes
Read evidence and context
Discussions that suspect a cause
1
0 original-poster resolution reports. Counts can overlap; they are not unique people or a success rate.
0 discussions have direct query context; 0 report a fix in that context. Other evidence may inherit the discussion’s subject.
Suspected cause
Based on the maximum load calculation on wikipedia (granted the formula is probably a lot more complicated but I am no expert and I am just guesstimate the width and diameter of each bearing)
Counts describe captured discussions, not unique people or a diagnosis. Author identities are not reliably stored. Exact duplicate evidence is counted once across matching discussions; one discussion counts at most once per action/state. Multiple repairs reported together remain a combination. Suggestions and failed attempts do not establish a fix. Matches cover whole discussions and can include related faults, model variants and incomplete threads.
13 eligible posts · 0 unverified posts · 1 discussions match the subject in their title or opening post.
Rennlist: 1 discussions
0 evidence records excluded for query context · 0 excluded by outcome qualification · 0 adjusted by outcome qualification.
0 acknowledgements have no verified action link; they do not establish a repair result.
Generation: 20261027T022239Z · outcome-qualification-6. Deterministic extraction; no AI model inference. How we use sources
I know of the most commonly accepted explanation as to why the IMSB fails: the seal lets out the grease, lets in oil+contaminants and doesn't let the contaminants out. The bearing then starts grinding itself until it explodes.
I'm being told by a shop that IMS bearings can also fail due to other reasons. Like uneven timing chain tension, or something like that. Do we know of any causes that can destroys IMSB's, other than contaminants getting in there?
Divation in cam timing due to stretched chains can be an advance warning of things to come. But, for most its just boom time and 25k up in smoke.
Do remember though that today no one has IMSB failure anymore. Montly oil changes have solve this design problem. For other 996 owners have choosen to put V8s in them (oil change not a problem) while many have a new retro fit IMSB (cant recall montly oil or quarterly recommended) and the remaining cars have been sold as parts cars.
This story is so long its now an mostly just an urban legend.
Expect some popcorn or no replys at all.
Well I have a car that is throwing the bearing out 13000 km after an upgraded IMSB fitment, and I'm discussing with the manufacturer (will not disclose which one) if I could simply have had a bad bearing eligible for warranty replacement. I'm being told there are other things that can destroy the bearing, like timing chain stress.. I'm cross-checking these claims with the experience of the forums
I like popcorn.
If an unsealed bearing is put into an engine that has had a failed bearing the new bearing doesn't have a chance unless the engine was stripped to bare cases and ultrasonically cleaned.
[Image-only post; no author-written text. Original image references:]
https://cimg7.ibsrv.net/gimg/rennlist.com-vbulletin/720x630/aliens_3fa6f0b21dca5e032c9f5fdef3eae3f9d3aeca31.jpg
There's an excellent 3-part PCA spotlight series that goes over basically everything you'd want to know about the IMS & IMSB issues, modes of failure, etc.
Part 1
Part 2
Part 3
"Originally Posted by fpb111
If an unsealed bearing is put into an engine that has had a failed bearing the new bearing doesn't have a chance unless the engine was stripped to bare cases and ultrasonically cleaned."
"It had a sealed replacement bearing, not an LNE unit."
disclaimer: I am not a mechanic and not an expert.
But I will speculate
IMOH (which is worth nothing to many), In my untrained eyes, the dual rows (early years) and the larger bearing (997) have less failures is the fact that they are able to handle more load. Other expert can chime in on the load at low RPM and high RPM vs the diameter of the bearing.
https://en.wikipedia.org/wiki/Ball_bearing
Maximum load
In general, maximum load on a ball bearing is proportional to outer diameter of the bearing times the width of the bearing (where width is measured in direction of axle).
Bearings have static load ratings. These are based on not exceeding a certain amount of plastic deformation in the raceway. These ratings may be exceeded by a large amount for certain applications.
Based on the maximum load calculation on wikipedia (granted the formula is probably a lot more complicated but I am no expert and I am just guesstimate the width and diameter of each bearing)
dual row has roughly twice the width and the same diameter of the single row which means it has roughly twice the max load.
larger bearing has roughly twice the diameter of the single row and about the same width which also mean it has roughly twice the max load.
Life of the bearing can be calculated here but of course I don't really know what I am doing here and if you really want to know, you can figure it out :-D
http://webtools3.skf.com/BearingCalc...103ACE16840128
This link talk about different type of bearing and I think some replacement product specifically mention thrust control now a day.
http://www.machinedesign.com/whats-d...een-bearings-1
This link talk about the different material used in ball bearing and why there is an advantage to go with hybrid ceramic
https://www.theengineer.co.uk/suppli...-applications/
Lots of confusion here. To OP, ball bearings are very sensitive to installation error; its why LN recommends particular shops. Force or shock in the wrong place will render a ball bearing doomed on install rapidly.
Apart from oil washing out the grease and going putrid and also acidic; if your IMS has bad run out it will stress the bearing and cause it to fail sooner. If you are stripping the engine down, get your IMS checked for run out.
This is a source reference. Confirm exact model applicability in the original material.
