Those 3 letters stand for something big – Intermediate Shaft (IMS). There has been much talk and information about it on the internet, some of it actually true, most just stories by people who have had a bad experience. Here are the nuts and bolts of it.
Porsche is no stranger to the IMS. Porsche has been using an IMS for along time. The 547 Carrera engine had one, in fact every 911 ever built has one. In the early engines, the IMS is known as a “layshaft” and does not present issues, even though it had the exact same job as the current IMS in regard to driving the camshafts. The problem is not the IMS but the IMSB (Intermediate Shaft Bearing) in the M96 and M97 engines.
Technical Information on IMS Bearing
Here is the technical aspect of the IMS and IMS bearing. The Intermediate Shaft (IMS) in the M96 and M97 engines is an internal engine part and is supported by the front console on the front end of the engine and then by a roller bearing on the back end, and sits directly below the crankshaft. The IMS is driven by the crankshaft with either a duplex chain or an internal tooth chain, providing drive for all 4 camshafts and the main oil pump. On the back of the Intermediate Shaft (the flywheel end), it is driven by the crankshaft. Also on this end is the timing chain for the 1, 3 bank (cylinder 1, 2 and 3). At the front of the engine, behind the crankshaft pulley is the timing chain for the 4, 6 bank (cylinder 4, 5 and 6), as well as an 8mm hex key that drives the oil pump. The driven end of the IMS (back of engine) is supported by the IMS bearing, a sealed roller bearing (not lubricated by engine oil). The front end of the IMS is supported by a plain bearing which is pressured fed by the main oil pump which has not shown to have any problems. The IMS bearing is held in place by a steel flange, bolted to the rear of the engine block. This flange holds the inside diameter (ID) of the bearing, so it has an outer race rotation, while the inner race remains stationary. The IMS bearing uses a center stud to provide a clamping force between the bearing and outer flange.
General Information on the IMS Bearing
This is what you as a Porsche owner should know of the IMS bearing. From 1997-2008 all M-96 and M-97 engines utilized the sealed roller bearing design which has exhibited frequent failure. There are 3 variations in design: the dual row bearing on model years 1997-1999 and some 2000-2001, the single row bearing on model years 2002-2004 and some 2000-2001, and the updated M-97 “big bearing” on model years 2005-2008. All of the three variations of the sealed OEM (original equipment manufacture) IMS bearings are prone to fail, some bearings, however are more forgiving than others.
Although these IMS bearings are internal engine components, most of them can be retrofitted without a total engine tear down, unfortunately, the late M-97 big bearing retrofit requires total engine disassembly. This is because in the M-97 engine, the outside diameter of the original IMS bearing is too large to be removed through the hole in the rear of the engine block. The only help you can give it is to remove the outer seal (behind the flange) and allow splash lubrication to the bearing to extend its life, but this is only temporary.
What you can do to extend the life of your IMS bearing?
Sorry to say, it tends to be the pampered pets and garage queens that suffer the most. Do not garage it; drive it like Porsche designed it to be driven. Do not be a tender foot. Use more RPM and wind it up once in a while. This will unload the IMS bearing and aid in lubrication. Note: 55mph is way too early for 6th gear; it shock loads the valve train of the 5 chain engine, thus transferring shockwaves to the IMS.
One of the most valuable pieces of information I can give you is to service your Porsche more frequently. Extended oil change intervals are not a friend as the elevated acid levels in used oil starts to destroy the bearing seals. I recommend oil changes at every 3000-5000 miles or at least twice annually. While you are there, have your mechanic dissect the oil filter looking for foreign object debris (FOD) – this is evidence of IMS bearing failure. It may cost a little extra for this but it is well worth the money to catch the problem early so that you can do something about it. You can even request to have the IMS flange removed to inspect the bearing; however, since this requires the removal of the transmission, it is not much more to just bite the bullet and upgrade to the retrofit bearing. Another option is install an early warning system like the IMS Guardian® which warns the driver if FOD is found in the oil. Further, on care, watch your oil temperatures and use the correct weight and grade of oil. Excessive numbers of cold starts contribute to fuel in the oil that is a solvent and breaks down rubber seals.
In this case, it pays to be pro-active. Look for oil leaks on your garage floor under your engine. Listen to noises, like rattles and get them checked out. You have paid enough for your Porsche. Do not let it be a stranger. Some of my best friends have been cars!!!. With all the info on-line you should have enough to go on to be pro-active and do something. If you ignore all the symptoms, and wait for catastrophic failure, it will be expensive. It is the epitome of pay a little now or pay a lot later. If you are considering any upgrade to your Porsche, you should really consider the IMS bearing if it applies to your model and year.