Intermediate Shaft Bearing Failure IMS Failure
Some of the most frequently asked questions about early water cooled Porsche boxer engines are, “how do I know when my IMS is failing,” “does my car have an IMS problem, and if so, do I need to worry about it?”. These are all good questions. I could try to explain this to you in technical mumbo jumbo, but you’d get about half way through it and turn the page. I’m going to do my best to explain it to you in layman’s terms based on my observations.
What is an intermediate shaft, you ask?
An intermediate shaft is used to transfer motion from one component to another, via chains. In this case, it is transferring motion from the crank shafts to the camshafts. It also keeps everything in time and rotating in unison, like the gears in a fine clock.
Early air cooled Porsche’s had a short intermediate shaft that is driven off of the front of the engine, transferring that motion to the cam shafts. Both camshafts are driven at the front of the engine. The shaft is supported by bearings that are lubricated by the engine’s oil system (Mezger Design).
With the introduction of the Boxster, Porsche went to a long shaft. This configuration drives 1 cam at the front of the engine and 1 cam at the back. It is supported at the front by an oil fed bearing and at the back by a sealed, self contained steel roller bearing. That roller bearing has it’s own lubricant that is meant to keep the bearing lubricated for the life of the vehicle.
Here is where the problem lies. Over time, the seals on the bearing fail, the lubricant that is meant to last the life of the engine escapes. Now there is no lubrication, and the friction destroys the steel bearing. This allows the the chains to become loose and come out of time. When the engine is out of time, pistons and valves “come into contact” (putting it mildly) with each other. Just like the gears in a clock, if they come out of alignment it will no longer keep time. Accept the consequences are more catastrophic with your engine, resulting in complete engine failure.
Which cars are affected?
All Boxsters from 1997 to 2008, Normally Aspirated 911’s 1999 to 2008, & Caymans 2006 to 2008.
996 & 997 Turbo engines are not affected by the IMS Failures. Their engine design is very similar to the air cooled engines (Mezger Design) & are not prone to failure.
What changed after 2008?
With the introduction of the 2009 models, Porsche redesigned or retro-designed their engines. They scrapped the long shaft design and returned to the original short shaft design. Bearings are lubricated by the engine’s oiling system, no longer rely on a self contained bearing.
Which cars have serviceable IMS Bearings?
From 1997 to 2004 all normally aspirated boxer engines have IMS’s that are serviceable. On the earlier cars, the most opportune time to replace them is during a clutch job, because in order to get to the IMS Bearing, the clutch & flywheel have to be removed. Unfortunately, on Tiptronic cars, there really is never an ideal time to do it. The transmission & flex plate will need to be removed. Later cars (2005 to 2008), require dismantling engine to replace the bearing. This is because the bearing can not be pulled through the case opening like the earlier cars. A boss prevents the bearing from being pulled out through the case opening.
How can I tell if my IMS Bearing is failing?
This can be difficult. Monitor oil leaks, especially from the bellhousing area. This could indicate that your bearing is or has failed. When bearing begins to wobble, oil will leak from the support shaft. You should have your oil filter inspected at every oil change. By cutting the end caps off, opening the filter up you can look between the pleats. If see any silvery metal in the pleats this could be a sign that your IMS is failing. The only problem with this method it is only a snapshot in time. Weeks or days later your bearing can start to fail, and you may have no idea. We have noticed that most failures occur with lower mileage cars, tiptronic cars, cars that are driven in lower rpm range. This is not to say high mileage cars or manuals are exempt from the problem, but it is a trend that we’ve noticed over time.
What else can I do to be proactive?
There are monitoring systems on the market. LN engineering (lnengineering.com) has developed an early warning system that can detect ferrous material in the oiling system. Once it detects the presence of material, it sets off a warning light. This allows you to shut the engine off, have it towed to a shop to perform an IMS Update hopefully in time. LN Engineering is at the forefront of IMS Bearing failure analyst & solutions. They currently have 2 retrofit options available. The first option is for single row or double row bearings. It is a Ceramic Ball bearing design. Ceramic bearings are harder, more durable than steel bearings. This is design is recommended to be replaced every 75,000 miles or 6 years. The second Option is a plain bearing that is oil fed, like the main & rod bearings in your engine. This setup is a more involved, requiring a new spin on oil filter, oil line installation & modification to the engine case. It is a bit more involved, but it’s also designed to last the life of the engine.
How to extend the life of your IMS?
First, DRIVE YOUR CAR! As stated earlier, the lower mileage vehicles seem to have the highest rates of failure. Second, drive your car like it was meant to be driven. Low rpm’s tend to be detrimental to the IMS. The analogy we use is, “you own a thoroughbred not a plough horse.” They are meant to be driven at the higher rpm range. We recommend keeping the rpm’s up above 2500 rpms. This may lower your fuel mileage, but if you’re concerned about fuel mileage, buy a hybrid. Lastly, ALWAYS do your routine oil changes. Splitting the recommended service interval in half, or changing your engine oil at least once a year allows us to keep an eye on debris in the filter, which is always beneficial.
So what can we take from all of this?
Earlier design had some inherent problems, but even then, the failure rate hovers around 10%. It is a bit of hit and miss whether your car will be affected or not. If you own an early car (1997 to 2004), it is a good idea to have your IMS updated, especially when performing any clutch work or anytime your transmission has to be removed. Have your oil filter inspected at every oil change & have your oil changed more frequently. If you drive your Porsche as a daily driver, we recommend splitting that interval at least in half. If it’s not driven as much have it changed once a year. Check for oil leaks noting where they are coming from. Finally, enjoy your Porsche! Drive your car, and by all means, drive it the way it was meant to be driven, Obey All Traffic Laws (wink wink), but keep the rpms up. SVR-PCA events, like tours and rallies, are a perfect way to stretch your Porsche’s legs. It may sound counterintuitive, but you’ll find the more you drive your Porsche the fewer problems you will have. Neglect and underuse are the enemies of all vehicles. Get out there drive and enjoy!
(This is an article by Nick Lettini of Frank’s Automotive for the local Porsche Club Monthly Publication) – http://svr-pcaor.org/wp/wp-content/Drifter/2017/201705.pdf
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