Doing clutch, not touching IMS
11-20-2018, 11:58 AM
#61
Drifting
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).
11-20-2018, 11:58 AM
#62
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
11-20-2018, 12:45 PM
#64
Shameful Thread Killer
Rennlist Member
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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.
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.
11-20-2018, 12:48 PM
#65
Rennlist Member
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.
11-20-2018, 12:48 PM
#66
Rennlist Member
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.
11-20-2018, 12:56 PM
#67
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.
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.
11-20-2018, 01:34 PM
#68
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.
11-20-2018, 01:34 PM
#69
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 .
Last edited by Vancouver996; 11-20-2018 at 02:02 PM.
11-20-2018, 01:41 PM
#70
Theoretically given enough hours the bearing will fail 100% of the time
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%?
11-20-2018, 01:42 PM
#71
Instructor
11-20-2018, 01:49 PM
#72
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.
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
Last edited by Vancouver996; 11-21-2018 at 01:09 PM.
11-20-2018, 01:57 PM
#73
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%?
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%?
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 .
Last edited by Vancouver996; 11-22-2018 at 01:50 AM.
11-20-2018, 02:00 PM
#74
Shameful Thread Killer
Rennlist Member
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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?
.
.
11-20-2018, 02:07 PM
#75
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 and high pressure use such as race track conditions .
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
the oem bypass doesn't just open if the filter is plugged , it also opens under conditions such as cold temperature start ups and high pressure use such as race track conditions .
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
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.