Q – What does the intermediate shaft do and where is it?

A – The IMS is located in the lower section of the engine block, below the crankshaft and it is driven by the crankshaft. It is connected to the cylinder heads via the timing chains and it also drives the oil pump on many Porsche’s. In some of the newest engines, it has been eliminated altogether.

Q – I have never heard of a problem like this on any other engine, why does it happen to the Premier sports car of my dreams?

A – I assume that like all car companies, there is a raging battle between engineering and accounting. If the engineers made all the decisions, the accountants say they couldn’t afford to build it. So we the consumer, become the guinea pigs and when the warranty runs out, we pay the tab…but I digress. The failure of the system is rooted in the use of a sealed bearing at the flywheel end of the IMS.  Sealed bearings are widely used in many parts of the car with great success. The problem is not the bearing itself, but the application in which it is used. A sealed bearing is filled with grease and the seal keeps the grease in (and presumably, contamination out). They are “lubricated for life” (oh yeah, I forgot, that is what marketing says!) The seals in these bearings rarely fail from the inside. The seal is usually breached from the outside. In the case of the IMS bearing, the outside is the inside of the crankcase which is bathed in hot, nourishing oil. (Confused yet?) The problem is, engine oil gets into the bearing past the seal, washes out the grease and leaves too little lubricant behind. The seal only allows enough oil in to do the dirty deed, not keep the bearing alive.

Q – Since you saw wetness at that seam, what should I do?

A – Now that the problem has become well exposed and documented, the oil leak at the rear of the engine should be checked out immediately.   It was common to blame the crankshaft seal for a leak not realizing that a failing IMS bearing would cause the IMS flange seal to leak.

Q – Can you hear the bearing failing? Is there any other way to detect it?

A –   My experience has shown that once you hear a bearing failure, damage is being done and in many cases, it is too late. With a stethoscope, we listen to the general vicinity of the IMS bearing at every service but usually the sound is subtle. I prefer oil analysis instead. A comment was made at the tech session that one could look for particulate inside the oil filter and I would take that concept a step further by having the oil analyzed to see what analysis reveals in the oil that one cannot possibly see with the naked (or even magnified) eye. Like the sound of a failed bearing, if you see particulate in your filter, you are in deep S*%$!

Q – What can I do to prevent it?

A – Change to a thicker viscosity oil of the proper Porsche specification. I use two brands here at the shop, Motul (French) and Pentosin (German), both are 05W40. Castrol Syntec 5w40 also carries Porsche approval. I still recommend Mobil One 0W40 for many cars but for these newer cars, I prefer the 05W40. On older engines, this recommendation does not apply so as always, follow the manufacturers recommendations!   I also recommend using the correct oil filter specified for the engine, not a generic substitute. Other than that, I do not know how to prevent it. If I owned one of this generation, I would budget and plan to do the bearing retrofit.

Q – Who do you recommend for the IMS bearing retrofit?

A – I would only choose an experienced shop that employs ASE certified engine repair technicians. Delving into the bowels of a five figure Porsche engine should never be taken lightly. This is one operation where experience counts.   I remember the first engine rebuild that I ever performed in1967. After three tries, I got it running but it never stopped leaking oil from the moment I fired it up. The moral of the story is: Don’t give this job to the “new guy”.


The IMS retrofit procedure isn’t much harder than doing an IMS flange reseal, so if the shop you’re thinking of using has done these procedures (as most that are familiar with Boxster, Cayman, or 911s are), a retrofit kit installation won’t be any more difficult than this. If your preferred shop is not on the list, have them contact us.

Why doesn’t the bearing on the other end of the intermediate shaft fail?

Well, there isn’t technically a bearing. The other end of the intermediate shaft rides in a bore of raw aluminum, splash oiled. Earlier aircooled Porsches and even later water-cooled GT2, GT3, and Turbo engines use split plain bearings (actually a VW Type 1 double-thrust camshaft bearing) that are oil fed on both ends of the shaft, with decades of proven reliability.

As supplied, the original IMS bearing employed a sealed bearing and relied on a permanent lubricant (grease) to lubricate the bearing. (Similar to the sealed bearing that fails in the gearboxes found in MY97-08 5 and 6 speed manual).

The problem with a sealed bearing with a permanent lubricant is that during the life of the bearing, the seal is subjected to oil temperatures near the maximum rating for the seal, eventually degrading the seal. At this point, the seal fails to retain the permanent grease, which is washed out by the engine oil. When this happens, the little amount of oil in the bearing is not sufficient to lubricate AND cool the bearing, leading to accelerated wear.

Several solutions have been suggested from more frequent replacement of the bearing and or seal and a lubrication schedule to replenish the permanent grease.

With our IMS Retrofit and IMS Upgrade, we chose to use a ceramic hybrid bearing which requires less lubrication and is designed specifically for poor lubrication environments. Coupled with the lack of grease seals, the new bearing is lubricated by splash as well as submersion lubrication

We do not recommend IMS retrofit kit installation as a do-it-yourself project – installation is best left to your trained independent mechanic or Porsche dealership. That said, typically the job is a billable 10-14 hours and average labor rates around the country are $140/hour. Later Tiptronic 911s require the engine and transmission to be removed together, so expect those cars to be very expensive when it comes time to do an IMS retrofit kit.By