USMC_DS1

Great technical data... keep this stuff coming Luxter.

Luxter

Thanks!
I like facts much more than just tales.

Yes,
http://www.hartech.org/buyers.html

Guide # 5 explains it all and it is very technical. Enjoy reading.

In a way, the IMS issue is a blessing for 997. In makes the owners aware of proper and frequent maintenance.

Cheers,
=L=

Spokane5150

Thanks Luster!

Luxter

Always happy to share my experience.

Palmbeacher

A substantial increase in load rating, yes. However the IMS bearing does not fail because of being over-loaded, it fails because it is under-lubricated. So increasing the load rating alone does nothing to prolong its life. Furthermore, the bearing is only "submerged in engine oil" whilst the car is standing with the engine off. Which is actually fortunate, because that is precisely what leads to failure of the seal and the wash-out of the grease. After that, the bearing depends upon splash lubrication thrown off the cam chains, which is nowhere as sufficient as spray lubrication such as the crankshaft bearings (and the IMS of the air-cooled and Turbo/GT engines).

Why the larger bearing fails less is due to it being a more substantial piece of kit, that is, because it is larger. The increased load rating is a consequence of the increase in size, and not really much of a factor in this application other than that the stud is less prone to snap. If the cage disintegrates and sends the ***** spewing into the engine, the same catastrophic failure would occur as with the smaller bearing.

Where the larger bearing is at a disadvantage is in so-called high-performance driving. Due to the increased diameter, each ball travels farther within the race with each revolution. So if the bearing is receiving inadequate lubrication and/or there is grease mixed with debris inside forming a grinding paste, the larger bearing will wear at an accelerated pace compared with the smaller bearing. At that point it is anyone's guess which will fail sooner. Perhaps the increased size of the later bearing is enough to keep it together. The fact is, of all possible solutions, Porsche chose the cheapest one, evidenced by the fact they used the same case and did not enlarge the portal enough that the new bearing can be extracted as the old ones could.

By the way, Hartech makes one extremely important observation about replacing an IMS bearing in-situ: If the OEM bearing has failed (or is in the final stage before failure) there can be significant damage and debris within the engine that a replacement bearing--no matter how well-engineered that replacement may be--may well fail prematurely. LN acknowledges that, especially since theirs is an open design, and cautions against retrofitting when the OEM bearing has failed or if upon inspection it show signs of breakdown.

My opinion based on engineering principles, is that the LN retrofit is best done prophylactically, whilst the OEM bearing is still in pristine condition. That and meticulous installation protocols should give the retrofit at least as fair a chance of long-term survival as the later, larger OEM bearing, if not more.

Luxter

Yes, LN also suggests that the debris collecting in oil filter canister can get past early opening bypass valve in the canister and contaminate oil even more.
That's why they suggest full flow oil filter with their adapter.
So, I guess we are back to proper and frequent maintenance.

user 72902

I have a close contact from the racing side of Porsche who explained the IMS issue. The original failure rate was 5% because the stud on the end of the IMS shaft was fragile and would brake off. Once broken it allowed the IMS to oscillate and this extra movement caused the IMS bearing to fail. The bearing was not the source of the failure rather it was a symptom. In 2001 the stud on the end of the IMS was beefed up and failure rates went to 1%. They continued to improve the bearing and reduced failure rates down to 1/2% until the IMS design was abandoned. Bottom line line is an engine 2002+ with an IMS has a 1%< chance of a catastrophic failure and like someone posted earlier nothing is bullet proof. I bet any car has at least 1% chance of a terminal failure for something - this topic remains over blown.

Spokane5150

Thanks for that balanced view. I think you're right about "Over Blown Topic"

PHX 911

From the size of the bearing ID, it appears that Porsche also increased the diameter of the shaft by 25%, at least in the bearing area. That's a rather large difference. Could be due to "overbuild" engineering, but if the shaft is larger in diameter along it's entire length, that would signifigantly reduce lash and angular forces applied to the bearing it's not designed to absorb.
I would guess the redesign involved the new bearing, and the IMS got beefed up quite a bit, too.

Alan C.

I spent the bulk of my career working with most of the automotive manufacturers in North America. A failure rate of 0.5% on my company's product would have consistently put me in the QC manager's office. Think about it. A 0.5% failure rate is equal to 1 in 200 parts failing!

Lvt19672

Drive it hard and maintain her and quit worrying about the ims.

utkinpol

speaking to those who tracks boxsters and 996 cars picture is not very clear. a lot of folks lost their motors, some folks never had issues and have close to 100k miles onheavily tracked cars, it is all hit and miss and due to overall ****ty design of m96 motor there are so many things that can go wrong there so it is very difficult to pin point what was the original issue. all in all it seems to be a usual picture - if motor was originally not balanced well, and none of m96/m97 get balanced in same way as gt3 motors get balanced it is all about amount of original vibrations and amount of secondary vibrations that get transferred to bearings.
as of cracks in rods and broken off rod bolts - again, it is probably all due to possible overtorque at assembly time, in my opinion, or due to amount of detonations if owner is negligent to gas quality.

what bothers me most - when ln eng shop rebuilds those motors using all proper parts they run those motors in the grand am series and none of those enginnes ever blew. so it is possible to make those motors work fine, and apparently only difference is to put in $5K worth of proper parts - good cylinders, good rods, good bolts, $300 bearings instead off $20 ones, etc.

realistically if by now almost everybody accept the fact that this IMS bearing has a limited life span - it has to be a recall campaign similar to what vettes had and factory should pay for labor to split the block and replace this part. it is not an acceptable scenario to have this problem and just wait for a bearinng to fall apart at 70k or 80k miles on a perfectly healthy motor.

Palmbeacher

Your deep-throat "from the racing side of Porsche" is wholly ignorant on the subject. Spindle breakage is not the primary cause of IMS bearing failure, and in a large number of cases it is found intact. The ***** and race wear as a result of improper and abrasive-contaminated lubricant, consequently causing failure of the ball cage. Only if a failing bearing manages, by some anomalous coalescence of factors, to run out-of-true and extremely hot for a significant amount of time without flying apart, is the spindle at risk of breaking.

rsabeebe

i think this is a key point - a failure rate (and we're talking about the total loss of an engine) of 0.5-1% is horrible. think about that, 1 in every 100-200 motors will grenade at the cost of $20k! from any manufacturer, that should be completely unacceptable. if this really is an accurate account of the failure rates [just from the IMS], i'm surprised Porsche isn't stepping in and 'helping' with the costs to replace the bearing. i guess one rationale is, who says a replacement bearing will eliminate failures, so why bother. obviously the cars are discounted due to the potential repairs one could see, but it sucks never knowing if your name will be called next. it's starting to ruin the experience of the car for me. i know, 'then get out'. i just can't believe some of you guys are accepting a 1:100 shot of your engine going south, unless you have an extended warranty that covers the IMS. i know a $20k repair puts me upside down in this car and the potential of that sucks.

rsabeebe

i'm curious, do you have an extended warranty? if not, you are absolutely a 'glass half full' guy. i would think it would be hard for anyone to overlook the potential of a $20k repair bill. you're clearly more of an optimist than i am.