Why the IMS bearing fails, another theory

[Jamesp]

I posted similar item in a string on Pedros IMS fix, and thought I'd put it out there on its own to get more feedback

I removed my IMS bearing and there was quite a bit of oil in the IMS tube. The shaft is not in the car, and yet no oil was seeping out past the bearing even though the shaft is stored such that the oil in it was being sealed in by the bearing end. So the IMS tube is effectively "sealed" by the bearing if the pressure between the inside of the IMS and the outside of the IMS is the same. My thought is that basic physics is at play here. Increased temperature in the IMS lowers the air density in the closed volume of the tube forcing air out at the bearing end. When the engine cools, the reverse happens and air, along with entrained oil enters the IMS tube. This slowly washes the grease out of the bearing by forcing oil under pressure through the seals, provided that is the path of least resistance into and out of the IMS tube. The IMS shaft is an unintentional pump which cycles a small amount of oil through the bearing end once with each engine heating and cooling cycle. The only inlet and outlet to this pump is through, or around the IMS bearing, and there is not much clearance around the bearing. I'm going to drill 2 very small breather holes through the meat of the driven sprocket into the open shaft area to eliminate the pumping action through the bearing, and allow a small exchange of oil in the shaft.

My fix is going to be: Breather holes, through the meat of the sprocket similar to IMS pinning holes (maybe I'll put in pins in as well, but I'll have to figure out how to do that correctly!) , A new greased bearing with an improved bolt - the stock bolt broke on this Box which is what killed the engine.

I believe the bearing design is solid (clearly not the bearing bolt though) provided the grease is not pumped out of it. I dumped a good 4 ounces (half a cup) of oil out of the IMS shaft. I suspect a good portion of that went past the IMS bearing seals washing out the grease.

Anyone have thoughts on this?

[Jake Raby]

You do realize what this would do to windage characteristics within the engine if enough oil was being moved though these passages??

Oil begins to enter the IMS shaft at stage 1 failure, it remains there through stage 2 and stage 3 and is only expelled at the stage 3- stage 4 transition.

[Jamesp]

Do you think there will be a measureable affect to the internal windage? The breather holes will be very small, in the range of 1/16 in. The shaft will have oil in it on start up, which will be expelled very quickly on start up and oil will be unable to re-enter when the shaft is spinning. I'm thinking of adding steel roll pins to get a doube benefit.

[KRAM36]

Would something like this also through the balance of the shaft out?

[Jamesp]

Not the way I modified the IMS shaft. I put several videos on YouTube yesterday explaining why the IMS bearing fails, and showing how to modify the IMS shaft to prevent pressure from forcing oil through the IMS bearing. I found it very strange that a German engineering company couldn't figure out a ball bearing. Ball bearings are fairly well understood from an engineering application perspective. How is it Porsche got this wrong? Several times at that. Something else had to be at play, and looking at it, the geometry of the IMS tube itself creates pressure which will tend to force the grease out of the bearing and replace it with oil.

Here is a link to the YouTube video that may explain why the grease lubrication gets forced out of the bearing 1 986 IMS Bearing Failure Mode - YouTube If you click on my "channel" you should see the rest of the videos showing the modification of the shaft. Just so you know - this isn't spam or an ad, I put this out there as information to other 986 owners. Happy Boxstering!

[thom4782]

Saw the video...interesting.n Here's my question.

Given the two holes are placed directly opposite each other, why wouldn't the IMS tube partly fill with oil for the following reason? At times when the engine is off, one hole will be submersed and the other vented. The surrounding air pressure will then pump oil into the IMS tube until the outside and inside oil reach the same height?

[Jamesp]

The shaft will likely fill with oil when the engine is off, though it is possible it won't. When the shaft begins rotating at idle the oil will be expelled out the holes. I thought about one hole (unbalanced) one through hole, and one almost through hole for balance (less oil in the shaft), or two through holes. I went with two through holes to move the oil out faster at idle. At the end of the day I'm not sure having the second hole all the way through makes any difference from an oil expulsion standpoint but it will balance more accurately.

[moresquirt]

jamesp i believe u are on to something here,while u have the engine out or at least the ims shaft is it possible to do a test run with your theory,if it works as planned then u could patent the idea and help alot of porsche people.i personally am on the fence with some of thease new theorys but feel if i do nothing then i am playing russian roulette,for about 18 grand last time i cheaked,for me that cost would be the end of my porsche experience.

[Jamesp]

Replacing the ball bearing entirely appears to be a bullet proof solution, and there is a product out there that does just that. Keeping a ball bearing leaves the choice of either a closed greased bearing or an open face bearing which depends on either splash oil, or an added oil feed. My thoughts on an open bearing (admittedly without much data) is it seems if your going to have an open ball bearing, a ceramic bearing with an oil feed would be the way to go. Its all about adequate bearing lubrication. Another option, which is where I'm headed is to relieve the pressure differential across the IMS bearing and go back to a greased bearing as the grease won't be washed out if there's no pressure differential across the bearing.

[Jake Raby]

Replacing the ball bearing entirely appears to be a bullet proof solution, and there is a product out there that does just that.

Yep. I invented it.
The ball bearing that isn't there, can't fail. The 11 wear components that are omitted also can't create further collateral damages. (read 3,000 words about it in the tech forum of the next issue of Excellence Magazine)

Through our development with the IMS Solution we found that oil pressure inside the IMS assembly can force the segments of the IMS assembly to disconnect and leave the engine with an IMS shaft failure.

Of course, most people don't understand that the IMS assembly is all lightly press fitted together and that oil pressure can force it apart hydraulically. Thats why the IMS Solution uses a block off that plugs the IMS shaft and partitions these segments that can separate under pressure completely.

Spraying uncontrolled oil inside the engine (and aiming it directly at a dynamically operating component!) of any sports car is the most horrible idea I can think of. It may be fine in an industrial application of a low speed steady state engine, but not something that sees 7K RPM and actually accelerates. Maybe they don't understand the inabilities of engine oil to maintain proper film strength for both hydrodynamic and boundary layer protection when aerated?

We learned that in 2007, before most of these new arrivals to this engine had ever disassembled one or even had the cam covers off. From now on we are going to patent all our bad ideas, as well as the good ones.

I see lots of air/ oil separators failing in the future and all of the engines will have a single common denominator.

[Jamesp]

Jake, Interesting. I hadn't considered oil aeration due to spraying oil into an operating open bearing. Kinda makes me take a step back to reconsider. Thanks for the insight.

[Jake Raby]

Originally Posted by Jamesp

Jake, Interesting. I hadn't considered oil aeration due to spraying oil into an operating open bearing. Kinda makes me take a step back to reconsider. Thanks for the insight.

Don't feel bad... No one else has either :-)
(among other things!)

I love your imagination and creativity.

[southernstar]

Jake, I can understand how on the intital start-up after assembly, there would be air in the bearing housing that could lead to some minor aeration in the oil. However, once the engine is running, the bearing is receiving a flow of oil under pressure and there should be no air left in the bearing. And certainly, there should be no air able to get into the bearing unless it has been improperly sealed.
Correct me if I am wrong, but shouldn't stirring of the oil by the spinning bearing only lead to aeration if there is air present that can get into the oil.

Brad

[mikefocke]

Isn't there air in the crankcase into which the high pressure oil is forced? When I turn on my shower I get a fog on all the adjacent surfaces. Air has picked up the liquid.

Wouldn't that oil spray lead to a heavier mist which would then have to be removed by the AOS as the air in the crankcase is forced through the AOS into the intake to make room for cylinder blowby?

Wouldn't the ball bearings and the relatively large gaps between them allow more flow through into the crankcase above the level of the oil than solid bearings as in "the solution"?

[JFP in PA]

Originally Posted by mikefocke

Isn't there air in the crankcase into which the high pressure oil is forced? When I turn on my shower I get a fog on all the adjacent surfaces. Air has picked up the liquid.

Wouldn't that oil spray lead to a heavier mist which would then have to be removed by the AOS as the air in the crankcase is forced through the AOS into the intake to make room for cylinder blowby?

Wouldn't the ball bearings and the relatively large gaps between them allow more flow through into the crankcase above the level of the oil than solid bearings as in "the solution"?

When running, the crankcase is operating under a partial vacuum (~5 inches of water), your shower isn't.

[southernstar]

Consider 2 stroke engines - even though oil is drawn into the combustion chambers during each cycle in conjunction with both gasoline and yes, air, nevertheless the oil is still able to provide adequate lubrication. This is so even though in theory there would be a significant risk of 'aeration' with the movement of the pistons and piston rings combined with oil and air.

Even in a four stroke engine, wouldn't there be a risk of the oil in the cylinders becoming aerated, especially during the compression stroke? The oil is still able to lubricate or none of these engines would be able to function for any length of time. Again, it seems to me that the risk of aeration from a pressure oil feed to a bearing with NO access to air intake should not be a concern.

And Mike, oil is being forced into the crankcase regardless, is it not? Since the same amount of oil is being cycled through the engine, I just can't see how this would make things any worse. Or am I missing something? It also strikes me that if the oil is being aerated by the pressure oil feed to the IMS bearing, then the oil on the dipstick should appear foamy or frothy after a hard run. Certainly if it was too much to allow the anti-foaming agents in synthetic oil to overcome. I wonder if anyone who has installed DOF has checked their dipstick after a hard run and can comment on whether this is case.

Brad

[JFP in PA]

Originally Posted by southernstar

Consider 2 stroke engines - even though oil is drawn into the combustion chambers during each cycle in conjunction with both gasoline and yes, air, nevertheless the oil is still able to provide adequate lubrication. This is so even though in theory there would be a significant risk of 'aeration' with the movement of the pistons and piston rings combined with oil and air.

Even in a four stroke engine, wouldn't there be a risk of the oil in the cylinders becoming aerated, especially during the compression stroke? The oil is still able to lubricate or none of these engines would be able to function for any length of time. Again, it seems to me that the risk of aeration from a pressure oil feed to a bearing with NO access to air intake should not be a concern.

And Mike, oil is being forced into the crankcase regardless, is it not? Since the same amount of oil is being cycled through the engine, I just can't see how this would make things any worse. Or am I missing something? It also strikes me that if the oil is being aerated by the pressure oil feed to the IMS bearing, then the oil on the dipstick should appear foamy or frothy after a hard run. Certainly if it was too much to allow the anti-foaming agents in synthetic oil to overcome. I wonder if anyone who has installed DOF has checked their dipstick after a hard run and can comment on whether this is case.

Brad

There are reasons these engines have multiple air oil separators in them.......

[southernstar]

I realize the engines have AOS, but what I fail to see is how direct pressure feeding of the IMS bearing, which has zero access to air, can increase aeration of the oil beyond what is already occurring.

Brad

[JFP in PA]

Originally Posted by southernstar

I realize the engines have AOS, but what I fail to see is how direct pressure feeding of the IMS bearing, which has zero access to air, can increase aeration of the oil beyond what is already occurring.

Brad

I would think that spraying an oil with some level of film strength onto a spinning and irregular surface would definitely entrain air into the oil, even in a partial vacuum, otherwise there would be no need for a device to separate them.

[southernstar]

Sorry, hit send accidentally on the screen. Doh! See above for what I was typing.