Straight Talk about the IMS Bearing in the M-96 and M-97 Engine

By Jay Coates

Published in the November 2012 edition of NNJR Porscheforus magazine, pg 28-29, revised in 2017 with new options.

Those 3 letters stand for something big- the 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 doesn’t 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 & 3).  At the front of the engine, behind the crankshaft pulley is the timing chain for the 4, 6 bank (cylinder 4, 5 & 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 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.  Up until recently, the M-97 big bearing retrofit required total engine disassembly. This is because in the M-97 engine, the outside diameter of the original IMS bearing is too large to be able to remove it through the hole in the rear of the engine block.  New procedures and updates have offered fixes, even for the M97.  One of which can be seen here:   

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.  Don’t garage it; drive it like Porsche designed it to be driven.  Don’t 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 annually.  While you’re there, have your mechanic dissect the oil filter looking for foreign object debris (FOD)- this is evidence of IMS bearing failure.  You can even have your mechanic take an oil sample to be sent out to analyze the metal in the oil.  One company that does this is Blackstone Labs.  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.  Don’t 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.

Rodent Rage
By Jay Coates

Published in the November 2018 edition of NNJR Porscheforus magazine, pg 20-22.

Last year, I received a phone call from a regular customer with a 2004 Carrera cabriolet.  (Let’s call him Frank.)  Frank stated that he had a dead battery on his garage kept Porsche.  We talked about methods of recharging that Frank could do on his own, since he lives 45 minutes away on a beautiful historic 80 acre farm.

After he charged his battery and started the Porsche up, there were some warning lights on the dash, so he brought the car in to us for a check over.  I connected the Piwis2 and found more fault codes than I had ever seen at once.  Upon further inspection, we found a massive nest in the engine bay as well as 20 pounds of dog food kibble under the intake manifold on the engine block.  Damage done by a rodent invasion. 

The rodent had quite a penthouse pad behind the right taillight assembly.  Ninety percent of the foam insulation that is usually above the engine, was now finely mulched into a big nest with plenty of dog food bits, broken wires (11 different colors), and topped off with extra urine.  The clean up became a near hazmat infectious task from hell.


Now Frank has been living on his farm for years, and so why now all of sudden, did this happen to his Porsche?  After talking to Frank, he shared that his 16 year old outdoor cat had just passed away a few months ago.  In addition to his outdoor cat, he also had two dogs, and he kept the dog food in his garage.  The death of his cat, the availability of a food source, and the comfort of a nice, safe, and warm Porsche was a natural attraction to a rodent. 

Frank’s car needed a rear main wiring harness, an engine harness, and new foam insulation.  The rear harness had to be made in Germany and was VIN # specific.  It took close to two months to have the wiring harness custom made, and then it was express shipped from Germany. Below is the custom-made rear main wiring harness.


Just for reference, the thick central part goes under the e-brake handle and almost all the interior had to come out.

Frank’s Porsche was not the first, nor was it the last.  Various 996s and 997s have been under siege of these rodents, especially because the cars are stored over the winter.  Rodents tend to go after knock sensor wires, oil level sensor wires, oxygen sensor wires, and the signal wire to the starter.  I have posted this issue to my Porsche tech colleagues across the country and the problem is everywhere, although in California it may be worse with some reports of rodents eating the plastic fuel tanks.

So the main attraction seems to be the wiring.  Since the early 2000s, many of the automobile manufactures have moved towards a more environmentally friendly wiring coating made from soybean which is a nice protein enriched snack for rodents during the winter months.  Yum! It happens in Toyotas, Mercedes, GMC, etc, but it is especially problematic for Porsche owners who store their cars over the winter making it an ideal place for these rodents to nest and feed.  The cost of repairs can run between a few thousands to tens of thousands of dollars, but on a good note are usually covered under homeowners insurance.

So what can be done?  I have asked my colleagues across the country for a range of solutions and here is what they have recommended to protect your investment.

▪       Place mouse or rat traps around the tires of the car.  Supposedly the rodent gains access to the car by climbing up the treads of the tire.  One colleague suggests placing one trap in front of the tire, one behind the tire, and one on top of the tire.  
▪       Rodent repellent spray (usually peppermint or pepper scented) can be applied to tires and inside the engine compartment.  You want to avoid places which might alter the smell inside your car.  One colleague described how a customer placed moth balls inside the car, which did not work, and now cannot get rid of the smell. Dryer sheets might work better.

▪       Have your engine shampooed before storing your Porsche for the winter.  The proper cleaner will deter these rodents and make your engine sparkle.

▪       Keep the lights on inside your garage.  Rodents tend to prefer darkness over lighted areas. 

▪       If you live outside of the more urban areas, get an outdoor cat.  Although I am a dog person with two Newfoundlands and don't know much about cats, my colleague in California recommends the “Maine Coon” cat, which is well known for its hunting skills.

▪       There are “car capsules” that encapsulate your car and protect it over the winter storage season.  There are various companies who make these in various designs.  One Porsche owner turned me on to this and he really swears by it.

▪       Rodent Tape—Honda has developed a pepper scented rodent tape with a special design of little mice with Xs on their heads.   The problem with this, is that it is difficult to get into the areas with tape.

One final note, it is recommended not to use mouse or rat killer as the rodent may find its final resting place inside your car.  And as one colleague from NC describes, “ I tell my customers not to use poison, because I’m not hunting for it when it crawls up in the dash to die.”  

Although I have attempted to keep this article light hearted, it is a serious matter.  Often times, we don't think about it until it happens.  So my recommendation is be proactive, keep an eye out for any evidence of rodents-- look in air filters, cabin filters, and look for misplaced nutshells or droppings, etc.  And as for Frank, he now has two cats, one is a spare, just in case.  Special thanks to Frank for his story and my Porsche tech colleagues for their input.




The Robust and Advanced Porsche 9a1 Engine
By Jay Coates

Published in the November 2016 edition of NNJR Porscheforus magazine, pg 12-14.

This article is intended to provide a brief, technical description of the Porsche 9a1 engine.

Main Differences from Predecessor M96 & M97

One of the main differences between the predecessors M96 & M97 is that the 9a1 engine has no IMS bearing or shaft.  The timing chains on 9a1 engine are located on the front of engine for both banks as well as a small chain to drive the oil pump. Because of this configuration the chains are longer and the timing chain speed is faster.

The engine block in the 9a1 engine is a monolithic-alusil (alloy material commonly used in sleeveless engine blocks, mostly used by German auto manufactures) with integral cylinders.  Its weakness is that it is not very forgiving to overheating and not able to be welded; however, its design is robust and powerful.  The 9a1 has 8 main bearings as opposed to 7 on the M96 & M97 engine.  The crankshaft of the 9a1 is forged and nitro-carburized heat treated with a .015 depth (as opposed to the M96 & M97 has heat treating of .003).  The crankshaft has 12 counterweights and 63mm main bearing journals.  Number 2,4,6 main bearing journals are grooved to supply oil; the rest are smooth. All timing chains and the oil pump drive run off the front of the crankshaft.  There is no crankshaft carrier in the 9a1 engine.  The main bearings are built into the block.


The engine block has a closed deck design as opposed to the open deck of the M96 & M97.  Just to note, the closed deck design is more robust; however, comes with higher coolant temperatures and higher oil temps under heavy load.


Pistons in the 9a1 are forged pistons.  The top ring land on the piston is hard anodized to handle the increased pressure due to the DFI (Direct Fuel Injection).  On the bottom of the pistons are oil squirters for cooling.  The compression ratio of the engine is 12.0:1. 

The oiling system on the 9a1 is an integral dry sump with 4 scavenger pumps. Oil pressure is controlled by the DME (Digital Motor Electronics) on demand. The DME recognizes combustion and responds with the correct oil pressure.  The returning oil coming out of the scavenge pumps will be foamy and needs to de-aerate which is done directly out of oil of the pump in anti-foam swirl pots.



The 9a1 heads are die-cast (not sand cast) which means that is a good method of limiting and/or eliminating porosity issues and maintains more exact tolerances since the metal is forced into the die under high pressure; however, as a result they cannot be welded.  There is no lifter carrier in the heads.  The lifter bores are integral to the head.  All 9a1s are variocam plus.  The camshaft has hardly no duration but has huge lift and ramp speed. The camshafts are shorter on B2 because the fuel pump drives off bank 1.   There are stronger cam caps, stronger gears (2014+ have module cam lobes like a 904 or a 4 cam Carrera).  There is 5 mm more valve lift on 911 9a1 as opposed to the 9a1 Boxster and Cayman.  Valves are bi-metallic with a 6mm stem and dual valve springs. Valve guides are short 31.75 mm or 1.25” long and made of Manganese (Mn).

The head gasket is a multi-layer steel coated with heat resistant plastic.  Thermal heat transfer is good.  There are coolant stabilizers to maintain and even coolant flow balance in the engine block. The water pump is a closed impeller-- pretty much overkill but nice to have. 

Direct Fuel injection

Fuel is injected directly into the combustion chamber under extremely high pressure (between 1400-1740 psi).  Fuel pressure can only be checked using Porsche Scan Tool (PIWIS  or equivalent tool). As previously noted, the fuel pump is driven off the front of the engine B1,  exhaust cam.  Advantages of DFI are engines can have higher compression ratio and run leaner mixtures.  The stratified fuel charge does not require long idle periods to warm up the engine.  


Conclusion: Best thing to do is go buy one, start the car and drive- keep the RPMs under 3k until the engine warms up which does not take long. Note: slow drives at low RPM are an unhealthy diet for this engine.  Burn good fuel and drive hard.  That is what this engine needs and loves. 


(Special thanks to Jake Raby of Flat Six Innovations and Tony Callas of Callas Rennsport for technical assistance and pictures.)





Technical Articles, all written by Jay

1. ​​Straight Talk about the IMS Bearing in the M-96 and M-97 Engine

2. Rodent Rage

​3. The Robust and Advanced 9a1 Engine


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