Hi all!

Proud first time Porsche owner here. It's an '03 C2 with 75k miles:



Since I got it, I've been driving the sh*t out of it, love it! First time feeling the "Porsche experience". The RR layout really is quite special.

I'm here to talk IMS though. I've been lurking around Rennlist and here for some time, and although only recently joined this forum, I've already read quite a bit about IMS related issues and the 996 in general. So here's what I think based on what I've read.

Pretty much every thread I read, "maintenance is the key", "Oil change every 5k" seems to be the most crucial factor in maintaining the health of your IMSB. Another common theme around here is that the IMSB tends to fail on cars with little mileage.

Given, I would like to propose another perspective.

I do agree that maintenance is important, however, I think the way one drives the car has far more impact on the longevity of the IMSB, or any other parts of the engine. I come from a modest engineering background, and I've built and tracked a variety of cars. From my limited experience in car/engine building and ECU tuning, I've developed certain driving style quite different from the general public - one that takes care of sport/race engines.

I noticed that in general, most drivers think pretty 1-dimensionally when it comes to their understanding of "engine stress." When I say engine stress or engine load, one usually associates it with RPM. Most people know not to rev their engines high when cold, but there's another dimension to engine stress/load.

In any modern fuel injected engine, the ECU uses a 2 dimensional map to determine how much gas to give, and how much advancement in ignition timing. A typical fuel map looks like this:



The axis on the right is RPM. The axis on the left is engine load. For naturally aspirated engines, the engine load is typically the same as your TPS (throttle positioning sensor) reading, which is essentially how much gas pedal you give it. For turbo or other force induction engines, the engine load is typically the same as your MAP reading, which is the vacuum or boost pressure of your engine. The mountain you see is how much fuel the ECU is giving the engine.

As you can see, an engine can experience a lot of engine load while the RPM is low. Taking the light purple color band for example, putting your foot down all the way at around 2,800 rpm is equivalent to lightly reving to 6,800 rpm.

In summary, this is how I drive my sport/track cars, and I believe the below steps should greatly improve the life of your IMSB or engine in general:

1. When I first start an engine, I give it at least minimum 30 seconds before I press any pedals, shift into any gears, or even lightly move it around. A cold engine requires some time to circulate lubricants around.

2. If I'm in a hurry (getting to work), I would starting driving, but gently on the gas. I would slowly bring up the RPM to warm up the car, but never much engine load. I've met countless people who stomp their feet on the gas pedal on an cold engine, thinking it's okay because the RPM is low. The engine experiences the most load when the RPM is low, with the gas pedal all the way down.

3. I never give it any serious gas until I know the engine is thoroughly hot, as in, a good 15 minutes of driving later. Also - don't trust your temperature gauge. The temperature gauges on almost all production cars are extremely middle-heavy. Meaning, the gauge needle is designed in a way that it pretty much never moves. From well below the operating temperature of an engine, a stock gauge would already show that it's "hot and ready to go". At this moment there is still a massive thermal gradient between the hot and cold parts of an engine.

Once everything warms up though, I drive it hard. I would redline it, stomp on it without care, because I believe that's what these cars were designed and built to do. Drive it hard, it's good for the engine.

I just want to bring the engine load concept forward to other owners. When the engine is relatively cold, or worse, when parts of an engine have reached operating temperature but other areas haven't, excessive engine load can destroy bearings, seals, and many many other things.

Some say that the IMSB fails because the bearing seals leak over time, and engine oil dilutes the bearing grease. I'm sure there's truth to this also.

Sorry for the mega post....

Howi

 

That's a nice analysis. Congrats on your purchase. Which part of socal you are buddy?

 

Thanks Kent! I'm in West Covina area. How about yourself?

 

While good overall 'engine care' advice and spot-on for oil-fed engine bearings, I don't think it has squat to do with this particular bearing issue.

It seems that the IMS bearing survives if either the original seals and grease pack remains in place or the original grease is washed away, but the bearing still gets enough indirect oil lubrication from being driven as a Porsche should.

That said, I am a pretty firm believer that the IMSB issue is overblown, and the best strategy is 1) good oil and shorter change intervals, 2) change the bearing if/when you have the transmission down for other reasons, 3) magnetic chip detector like IMS guardian to give you a heads-up if the bearing cage is failing before it lets loose tiny marbles into your engine.

 

I'm soon buying my first Porsche and have been reading as much as possible. Any maintenance strategy goes out the window when one buys a used vehicle. Unless you know the previous owner, you have no idea how this vehicle was driven (warm up, oil change interval, etc.)

I am operating under the assumption that my "new" car was broken in and driven by a 16- y.o. Senna wannabe and maintained by his Xanax-addled, trophy wife mom.

I'll do the mod asap and engage in conservative oil changes. Cheap insurance, IMO.

TC

 

I think we're on the same page here, but somehow you think it's irrelevant. That's fine, to each his own.

I come from building and tracking the most notriously unreliable engine ever - rotary engines. In comparison, the IMSB issue is nothing to sweat over. Just take good care of it by having good driving habits.

Howi

 

Only because the IMSB is a sealed, non-oil-fed bearing. A rarity for internal engine components.... It's like saying a gentle warm up will make sealed bearings typically used on external engine components last longer (belt pulleys, alternator, etc).

Unlike an oil-fed bearing, I don't think a sealed bearing knows or cares if you are redlining the engine at full throttle seconds after startup or warming it up gently for 20 minutes with gentle throttle usage.

Did your race rotary's have any critical bearings that were sealed instead of oiled?

 

Howi--I just re-read your original post. What you are describing is what my driving instructor (Dad... ) called "lugging" the engine. I've always nursed the revs and speed up so your method is perfectly natural.

I'm also a "warm up ****". It bugged the crap out of me that people would just jump in the car in the morning and blast off. (The ex does that--:0 ). How would YOU like to jump right out of bed on a cold morning and blast off into a sprint?

Thoroughbreds need a thorough warm up. They need to be ridden a specific way. If you take care of them, they will perform.

(Off the non-engineering degree soapbox! )

TC

 

That's close bro, I am in San Gabriel. So if I see a grey 996 coupe on the 10 freeway, there is a big chance you are the driver, haha
Btw, if you change your current orange corner light to clear ones, that would be much nicer.

 

Thanks Howi, nice post. I, too, let my cars "warm up" before even putting them in reverse to back out of the garage. Same goes for my Z06.

 

Good point pfbz.

I just would like to point out that the IMSB is such an important part of the operations of the engine, unlike a pulley bearing. Further, the IMSB experiences considerable non-axial twist and thrust loads. Remember the IMS is driven by the crank on 1 end, while the 2 ends of the IMS are driving the cams. Lots of complicated moment (torque) on all 3 axis happening there. I imagine that thermal expansion of the parts would play an important role in that area.

Some good information on how loading affects bearings here:
http://www.applied.com/site.cfm/Bear...y_Hold_Key.cfm

This is the a quick summary here:
Similar information can be found on most of the major bearing manufacturers' websites.

The load effect is further complicated by, as you know, the leaky seal. Over time on a leaky IMSB, the bearing is pretty much lubricated on exclusively regular engine oil.

I strongly believe that it's wise to give our beloved 996 a gentle warm up. If need be, lightly bring up the RPM until the engine fully reaches operating temperature. It's much better than stomping on the gas pedal at a low RPM.

As we speak, my 996 is getting its IMSB changed to the LN Engineering bearing.

Howi

 

Awesome! Do you drive the matte black Turbo or C4s in your avatar?

I'll take a look into the clear corners... Thanks for the advice....

Howi