The Other End of Your IMS

Yes, we all worry about that awful bearing on back end f our intermediate shafts. Did you ever stop to think about the other end? It's comical. It just rides in an aluminum casting! And drives the oil pump! No bearings or bushings allowed

The plain bearing end of the IMS shaft is the "correct" way - the IMSB only exists because Toyota helped Porsche realize that doing things correctly costs more, and any issues resulting from NOT doing things correctly can just be passed along to the consumer.

I would not call a shaft stuck in a recess in an aluminum casting a "plain bearing" but I guess you could. The references in the past all suggested there was a "proper" bearing on the other end. Thanks for posting. Learn something every day here.

The following sounds dickish; even after trying to un-dickish it, it still comes across a solid 20% ***-y. Sorry about that. I'm not sure what the Rennlist definition of a plain bearing is. As far as the rest of the known universe, a plain bearing involves two bearing surfaces sliding past each other with no ancillary (*****/races/bushings) parts. The non-IMSB end of the IMS is actually a great example of a plain (journal) bearing. As long as there are no *****, cages, bushings, etc...it's a plain bearing. That's not even an opinion - that's the definition of a plain bearing. *Edit* Even Wikipedia agrees...like that somehow makes it more legit. A plain bearing (in railroading sometimes called a solid bearing) is the simplest type of bearing, comprising just a bearing surface and no rolling elements.

There used to be a biker bar out my called "The Other End"

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That damn stroke acting up again? Sorry, I'll translate: "That [drool] damn stroke kitty kitty?" Heh.

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Now your talking my kind of language! I assume the reference is to a "side bearing". Might I inquire from what source you secured that info, WIKI?...Wait, never mind I forgot...

Ok we're talking about journal bearings on the wheel set. Fortunately or unfortunately most freight cars are now roller bearings. Because of numerous catastrophic failures railroads have invested millions and more $$ to install wayside heat, vibration, noise and other expensive detectors to try to catch failing roller bearings before the axel burns off causing all sorts of bad things to happen. If you think a failed IMSB is bad should see what a burned off journal causes on a loaded coal train when it occurs at 45mph! Never mind I still have flashbacks to that unpleasant part of my life...Carry-on. BTW Plain bearings have/had their issues as well. Not the best environment for an oil wetted bearing.

*out my way. Don't go their

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I've read that that end has pressure lubrication. Are there not any oil holes on that end? I thought that oil pressure lubrication is required for a plain bearing to work, unless there's some other means to get oil in and out of that location.

"Plain" or "sleeve" bearings are friction type bearings, where "ball" are anti-friction type bearings. A sleeve bearing has no relationship between the number of revolutions and life of the bearing. The bearing could last forever if properly lubricated, it is supported between the two surfaces by a wedge of oil. Or it could fail during start up due to lack of the oil wedge being present, this is why they say the majority of engine wear happens at start up. If it does not live in the area where the oil is to feed it (normally dripped in from the top), then it needs a pressurized source of oil. I know a lot about electric motor bearings, which most are drip lubricated, don't know a lot about how the M96 engine bearings are lubricated, but assume they pretty much all have a pressurized source of oil. With an anti-friction or ball bearing, life is proportional to the number of revolutions, every time it goes around, it's closer to end of life. However, they are normally sized and selected to last for a long time with proper lubrication. Bearing life is not consistent over a batch of bearings, some fail before others. Just like a light bulb life. I always wanted to see the other end of the IMSB shaft, I would assume that any axial thrust loads on shaft are absorbed by the intermediate shaft bearing, the side with the sleeve bearing would only have the ability to absorb thrust going towards the front of the engine, and the shoulder is so small it does not appear to be a thrust face. I also always wonder what is "thrust control" on a roller bearing, as roller bearings basically cannot absorb axial thrust forces. This is what Vertex says in their advertisement. Just never figured out what thrust control was in that case. This is why you would want to change your IMSB before it fails, people say they are "perfect", but they are not, they are fatigued when they come out, most likely have minor defects that have developed over their lives, but the cage is still in place and the defects are small enough where the bearing still performs as it should.

I just add a little grease to that bearing while hitting up the front suspension grease fittings. Simple and I sleep well at night.

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I believe it interfaces to one of the two rotors that pump the oil, there is no seal between them, so it looks like oil get forced through the gap and leaks down into the sump lubing the plain bearing as it goes.

This isn't "comical". It's common sense. I noted this 15 years ago, then I invented the IMS Solution. Note the length and diameter of that end of the shaft, then look at the IMS Solution flange. This is a plain, journal bearing, pressure fed with oil. Just like the Solution. I have only only seen that end of the IMS fail once, and that was due to debris contamination between the surfaces.

If that bearing scares him, we better not tell him about the cams....

Jake, if I correctly understand your thinking, the real problem with the IMS may not lie at either end of it, but instead in the middle, i.e., the trueness of the shaft itself.

Your cams all run on the casting, no bearings, so do aircooled 911 cams. Cams, IMS are all spinning at half the speed of the crank. I'd have to look to see if the IMS has a oil galley, but if it doesn't I'd say the pump leaks enough to lube the journal by design. IIRC it has a groove for oiling.

Its just one of the surprises I found when rebuilding my engine. And yes, there is a lot of oil fed to it. But, as you can see by the gear, that end drives the timing chain for the left side head. There's a good bit of axial tension on it, so I'm wondering why it doesn't end up egg shaped. I was not as amazed at the cams not having bearings. Even though you have the tension of the valve springs, it seems the journals in the heads and valve covers are more than up to the job. You'll find many oil passages there. I didn't do much research before I bought my 996. I never considered the term "disposable engine" possible. After doing my rebuild I can fully understand why the Porsche dealers do engine swaps on these and not rebuilds. I must admit that coming from a background of simple V8s, this thing was an eye opening challenge. But I had fun and enjoyed it!

I really wish that these engines - all engines - had pre-oilers and focus more on filtration and using a pre-oiling system to reduce wear, since most wear is during startup.

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Or out for a train inspection at 3am after an undesired emergency application when the lamp beam illuminates a caustic soda tank dug into the ground surrounded by twisted broken rails and the glowing remains of the truck and journal assembly. Been there with the coal train also. Sixty miles an hour on double track. No flashbacks but the occasional "train dream". All in the past once we pulled the pin and carried on. Nothing to add regarding bearing surfaces. Just sharing ribbons of steel stories. Move on...as you were.

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Yep! Me too...