aviography

^ IIRC the later "improved" 997 bearings are larger diameter than the M996 engine.

tlisotta

Ok. That clears it up. So more than likely the 996's I am looking at they say that Porsche upgraded the IMS - it is probably an LN Engineering one. I also assume they would put the sticker in the door that says LN and the date of install.

JD ARTHUR

I think the dealer may be telling you Porsche updated the bearing meaning it has the new larger bearing that can not be replaced without tearing down the engine. If they say that they actually replaced the bearing then that would imply that it was an earlier style motor with the smaller single row bearing to begin with and it is able to be upgraded in a couple of ways. Ask them for documentation on exactly what was done.

tlisotta

Thanks. I will do some more digging. Appreciate the replies.

Spokayman

The larger Porsche bearing that debuted in about 2006 can be installed in the 996 (M96) engine.
That's the bearing my '01 C4 currently has.
The Porsche dealer installed it for the prior owner in 2011 when something went wrong in the engine.
To install the larger bearing, the engine case must be split in half.

JD ARTHUR

I would think that in order for the late model larger bearing to be installed in an earlier case the case would require machine work and I don't see any advantage to that but maybe I'm wrong. Maybe Jake will add something to this.

Spokayman

I'm not aware of any machining that is required.
From what I have read Porsche factory remanufactured engines from around 2006 and later used this larger bearing as did all M96 engines coming from the factory beginning sometime in 2005.
There are at least hundreds, probably thousands of these remanufactured engines out there in 996s; 986s; and even early 987 Boxsters and 997s.
There have been a couple of threads on this forum commenting on these engines, denoted by the letters "AT" included in the engine number.

I am open to correction if I have misunderstood any of this.

Also, I am not saying that these newer larger bearings are better than the LN bearings or any other replacements on the market. Thus far history has shown them to be much better than the earlier single row Porsche bearings, but I have read of a couple failing in 997s as well as one in a Cayman.

JD ARTHUR

I am just assuming that since the later model cases have to be split in order to replace the bearing that they wont fit in an earlier case because the hole in the earlier case is to small. It seems to me that early and late case's are different in at least that area and some machining would have to be done to make them alike before the late model bearing would fit both.

Flat6 Innovations

To facilitate the M97 IMSB being fitted to an engine previously outfitted with the M96 diameter bearing, the engine must be completely disassembled. It goes further than splittinge the case, as the IMS is the 3rd part thats installed into a freshly assembled, and the 3rd from the last to be extracted when disassembling. We do a handful of M97 IMSB preemptive retrofits every year, fitting the IMS Solution to them.

The standard procedure would be to replace the entire previous IMS shaft assembly with one from a 2006 or newer engine, or a new uinit from Porsche. The later unit was developed to be applied retrospectively with all engines built before mid year 2000 when the IMS drive changed from a duplex style roller chain to an internally toothed type chain.

So.. If someone owns a 99 or early 2000 996, they'll get a nasty surprise when they take the engine apart for this procedure, as they'll learn that their crankshaft is not compatible with the later IMS assembly.

There's nothing magical about the M97 bearing, its 26% larger diameter, and the surface speeds the bearing sees at lower RPM is more favorable to unloading of the bearing. All the M97 IMSB did was move the failure point from lower RPM street cars to higher RPM track cars, as the IMSB then operates at a speed thats not optimum for it's diameter. We have notoriously pulled apart m97 engines used for Grand Am and World Challenge and replaced their IMS assembly with a M96 style.

The later M97 IMSB cannot possibly be fit to an earlier M96 IMS shaft, as the housing bnore of the shaft cannot be modified greatly enough to allow for this.

tlisotta

So - dumbing this down for me - could a 2004 996 C4S owner have had the upgraded "Porsche" bearing installed with a rebuild of his engine? He is adamant this the case from Bruma Porsche in Jacksonville. He had a major oil leak and dropped it off at Bruma - he has all the receipts. After that he had a second leak and then took it to your shop. Jake - this was the car I had PM'd you about your shop took a look at. I will email the gentlemen next week you told me to that worked on it. This is key in that I am not interested in the care unless it has an LN IMS that is replaceable. I am also probably staying away in that he had a leak before he changed the IMS out and then he had a second leak. If I could feel confident about this car - I may make an offer but sounds risky.
Car is below (a lot of great upgrades -tracked about 1/4 of the time):

https://www.pca.org/classified-ad/304522

Flat6 Innovations

Yes, once the engine comes apart, anything is possible in regard to IMSB.

I had directed you to Jud, my General Manager. The first thing he will do before releasing any info about the car is gain consent from the current owner, who had the work done here. We release no information without written consent. Once we receive this, the documentation can be linked via Dropbox for all our procedures.

tlisotta

Yep - understood. He sent me the invoice from your shop so I will tell him to send Jud a note.

DrBrain

My car (C2, 2004, IMS failure at 46k) passed 35k miles on the updated bearing without no problems and very good used oil analysis reports. It's my daily driver, the broken engine was repaired by porsche San Antonio.

Ben Z

That definitely fits with the science. Another thing is that the increase in diameter magnifies the lateral force of any imbalance which might happen to be present.

BobRickel

I bought a 1997 Boxster with 43K miles a few months ago. I had seen so much about the issues that suggested that low mileage cars were more susceptible to having a problem that I decided for the peace of mind that I would change out the IMS, RMS, water pump, belt, plugs and tubes, AOS and filters @ the same time. I searched a lot on the IMS issues and what would be the best way to go. My indy mechanic who was factory trained in Germany and worked for a dealer in Jacksonville for 14 years suggested the EPS repair. I had it installed and it seems to be running fine. Here is a video that convinced me.
My mechanic only charges $1400 for the complete EPS IMS repair.