Palmbeacher

Well, according to LN's website it's now up to four, and one might infer from them embarking on a revision, that they're concerned about more failures being likely.

I'm not particularly comforted by their "99.9%" success rate, given that it takes in their dual-row and their engine-apart-upgrade which they claim have had zero failures. I'd like to know how many single row bearings they've got out there, and then recalculate the failure % those four amount to. Even then, my suspicion was, and now is even stronger, that the major cause of IMS failures on OEM bearings--and the reason there aren't more of them as one would expect if it were indeed down to a defective design--is an assembly defect. I personally believe that there are excessive tolerances in the way the bearings press-fit into the shaft, and/or the stud lines up the axis of the bearing bolt through the flange, which causes those particular bearings to run hotter and/or out-of-true and that in turn causes them to deteriorate rapidly and fail prematurely.

96redLT4

I think my build was about 04/05. Actually I am not really that worried. I was just sort of trolling the water to see what issues other early 997.1 owners have now had...
Jim

mattyf

^ This or something like this. A couple of rules/things to look for when designing stuff: tolerance stack up and always preload your bearings.

Tolerance stack up can cause things that should line up to be off if both parts happen to be at the extreme limits of there tolerances. Like you described parts may not be concentric, could cause wobble or something like that.

Bearings are designed to be preloaded. The preload keeps the ***** in contact with the races and allows them to roll in the bearing as opposed to slide. It's when they slide that you get trouble and premature wear. (as an aside this is one reason why I never understood the double row, it seems it just increases your chances for sliding contact). I'm not exactly sure how it's possible to preload the IMS bearing due to the design only having a ball bearing on one side, but one could guess that with tolerance stack up some cars run loose and don't get the proper preload. That combined with a seal that fails and lubrications loss could be your culprit.

I guess what I'm saying is I agree it could be specific to individual unlucky cars and not systemic to the whole line, as it seems from the low failure rates.

pissedpuppy

997.1....the new 996

alexb76

Ok, so you gold the old design (more prone to fail), and since you're kind of worried, I would investigate the cost of LN Engineering bearing upgrade to see if you think it's worth it for you or not.

Some pointers from LN Engineering on how to prevent failure on old designs:

- DRIVE THE CAR. Car that sit idle have A LOT more issues
- Every once in a while make sure you really push the car, to get the temps up and get all the crap out of engine
- Ensure you use very high quality oil and change frequently (LN Engineering recommend Motul 8100 X-cess 5W40

Palmbeacher

A wheel bearing carries a share of the entire weight of the vehicle, and subject to forces from continual changes in axial angulation, and impacts from road irregularities. Today they are sealed, and yet last the lifetime of the vehicle. The IMS bearing is supported at one end by the IMS shaft and the other by the axle bolt. Assuming the chain tension is equal on both sides, forces acting perpendicular to the axis of the shaft and bearing should cancel out. In other words, the IMS bearing shouldn't really be taking a beating it can't withstand, not even the least load-rated 2001-2005 single-row. However, if the bearing axis is not exactly parallel to that of the IMS shaft (either because of improper fit of the outer race into the shaft, or misalignment of the flange and its hole through which the stud is bolted) then it's not hard to see where there would be increased and uneven load on the bearing, which could lead to premature failure. It also would completely explain why some IMS bearings have failed at very low mileage, and some are still serviceable at 100K miles and beyond. Other proposed theories, like length of service intervals, driving habits, etc. are only partially explanatory.

If I'm correct, then the condition of the old bearing being removed would corelate to the prognosis for longevity of the replacement. That is to say, an OEM bearing with, say, 50K miles that shows signs of wear could indicate a misalignment is present...and therefore the owner would be smart to inspect the replacement LN bearing prior to the next 50K interval. Whereas someone whose OEM bearing comes out with little to no wear might expect the LN replacement to last much longer.

Of course, most likely there are multiple variables at work at once, and whilst misalignment could be the root cause, those other factors may very well mitigate one way or the other and to varying degrees of magnitude. Certainly the open bearing design (LN) will be even more sensitive to oil change intervals than a sealed design. Likewise, it being vulnerable to debris entrapment, I think LN would be well-advised to include in the retrofit installation protocol, flushing the crankcase thoroughly before the new bearing is installed.

Neotorque

@Palmbeacher

You raise an interesting point. I wonder how many, if any, of the four LN failures occured in cars where there was already some indication of a failing bearing (for example, through their Guardian system). If so, it would suggest that the failed LN bearing is not to blame (nor is it necessarily deserving of credit in cases where it does not fail).

In any event, it seems pretty clear that the rate of failure is extremely low (probably under 1%), which is certainly no comfort to those who've had one fail, but it should comfort the rest of us.

blk on blk

i too hav a launch car, daily driver. has 31k on it now, and to date i have replaced my battery cables and.....nothing else. had the car 6 years.

SteveFromMN

Well it is probably true that the pre 997.2 engines were not the strongest Porsche ever made, I just traded my 996 in after 12 years and 50,000 miles with no troubles. Bought it new in 99 so all of them do not fail.
Will it? I will never know. But it gave my 12 years of trouble free fun. Just enjoy your car.

Jay H

We'll probably never know, but it would be interesting to know what kind of failures or wear Porsche experienced in the test mules and while bench testing the M96 motors back in the mid '90's.

utkinpol

it is difficult to speculate of what would be better way to deal with it.
history shows that this original dual row bearing was a weak spot on big enough number of cars. my car is on new single row OEM bearing so it does not apply to me.

most people with 996 cars I know did LN retrofit. I would probably did the same. For you I would recommend to check on 996 forum on this topic and would trust mechanic who services car for long enough time.

any mechanical component has a limited time to next failure life expectancy and exact moment when it will fail depends of many factors, street driven cars have this limit high enough not to worry about it but we read from time to time about motors granading, for whatever reasons. imho if car is getting run regularly and in reasonable way - hard but with no abuse and it ran fine for many years and has no rattles, etc - why to worry?

at each oil change send old oil for review - if you will start getting increased metal particles there it will be a sign to take care of things. but, again, many people did this and got failure with no warning signs. others drive those cars like lexuses, for years. go figure. i am trying to prevent what i can prevent plus hopefully will always have spare $20K for new motor, worst thing is to make wife aware of this 'additional' danger to family budget. for myself i simply factored in additional $20K reserve as a part of car`s ownership price. It is still better than a $60K for a new gt3 motor if it gets blown with no usable core. if we`ll speak money it is a very simple choice - your car plus spare $20K for new motor or your trade-in car value vice new GTS purchase price. do the math and decide if you can afford new or prefer to run old. I am choosing to run my old one.

Aerokitted

All cars will fail without remediation/maintenance/upkeep.

I wouldn't worry.

alexb76

+1

cibergypsy

Yesterday I went to my dealer and got these quotes (numbers approximate as I didn't write them down exactly and are what I remember): 996 GT3 new motor is $60k plus change, remanufactured is $38k plus change. 997 GT3 up to 2010 is $58k plus change new and $37k remanufafured plus change. The X51 motor on my 2006 Carrera S would run $19k plus change remanufactured with a $22k core charge or $41k + without core. In my case, I can get the engine from the dealer for $16,800 remanufactured, with the applicable core, so I'm keeping my 997 for the time being. All motors eventually die so, for a lot less than any GT3 motor would cost, I can get the car running again in the distant future - I hope very distant - if I still own it.

What surprised me is that a sans-core X51 Carrera S motor costs over $40k! Hopefully, if it ever came to that, my motor can be used as core. Otherwise...

gota911

The IMS grenade is the main reason I passed on some sweet 2008 997.1 cars to get a 997.2.