Pedros Techno DOF IMS fix?

[Jake Raby]

Originally Posted by Jager

Cracks in the bearing cage? Various frequencies created as a result?

Nope.. But this could increase load on the cage and lead to premature failure :-)

[Jager]

Originally Posted by Jake Raby

Nope.. But this could increase load on the cage and lead to premature failure :-)

Are you seeing a build-up of some kind on the bearings??

[moresquirt]

Jake,do u believe that regardless of how well the bearing is lubricated (ie DOF) the inevitable is bearing failure eventually regardless off single ,double ect. From what ive read
it would appear that lack off regular oil changes,wrong oil viscosity,driving at slow paces in higher gears,staying at 3000 rpm for extended intervals ect all will contribute to earlier failure but basically at standard bearing in this application is a bad idea and nothing but taking the bearing out off the equasion is the only SOLUTION!!

[Jake Raby]

Originally Posted by moresquirt

Jake,do u believe that regardless of how well the bearing is lubricated (ie DOF) the inevitable is bearing failure eventually regardless off single ,double ect. From what ive read
it would appear that lack off regular oil changes,wrong oil viscosity,driving at slow paces in higher gears,staying at 3000 rpm for extended intervals ect all will contribute to earlier failure but basically at standard bearing in this application is a bad idea and nothing but taking the bearing out off the equasion is the only SOLUTION!!

Based on my direct experience the problem is the application of a ball bearing. The constant that I have mentioned in this thread applies to every IMS Bearing equipped engine from 1997-2008.

Opinions will vary and mine is very biased. Some contend the exact opposite of this.

The attendees of my class just learned of this constant today. Their jaws dropped when I held the bearing in my hand and illustrated just one thing. I could see the "dots connect" pretty quickly, then came the comments.

Tony is going over the IMSR procedure now in class :-)

[Jamesp]

Jake,
Any idea of the typical run out on the IMS driven gear? I had the failed IMS from my engine measured at 0.015. Quite a bit for a gear, but as it is a chain drive if may be ok. In any event that was a major driver in replacing the damaged shaft with an undamaged one. My thought at the time was if the IMS gear run out was poorly controlled in the design, additional side loads could shorten bearing life in high run out cases even with a deep groove ball bearing.

[Jake Raby]

Originally Posted by Jamesp

Jake,
Any idea of the typical run out on the IMS driven gear? I had the failed IMS from my engine measured at 0.015. Quite a bit for a gear, but as it is a chain drive if may be ok. In any event that was a major driver in replacing the damaged shaft with an undamaged one. My thought at the time was if the IMS gear run out was poorly controlled in the design, additional side loads could shorten bearing life in high run out cases even with a deep groove ball bearing.

Good thought that few consider. The acceptable runout is less than 1 thou. for my engines.

Too much runout, and the associated timing chains see accelerated wear as well as the replacement bearing. This is one reason why we highly discourage cutting the race of a failed bearing out of a shaft and resurrecting it, because the heat and trauma associated with bearing failure often creates runout that can lead to shaft separation or future bearing failure.

One supplier of "rebuilt shafts" is selling shafts with another bearing design that have previously failed and have been "repaired". We'll see how that works out for them and the buyers.

[southernstar]

Jake, without getting into semantics, surely you must agree that the problem is a combination of the original bearing design/s AND inadequate lubrication. Indeed, even on your own site you highlight the same under the heading IMS Failures Explained:

"Next, while the grease seals may still be intact, the permanent lubricant inside the housing has been dissolved. The compromised grease seal now provides a barrier, preventing the seeped-in engine oil from leaving the chamber, but also preventing enough fresh engine oil to enter that might cool and lubricate the bearing surfaces." Then "as inadequate lubrication, extreme heat and corrosion continure, mechanical deterioration accelerates."

IMS Failures Explained

I can only assume that you continue to believe, based upon your likely unparalleled experience in rebuilding M96 and M97 engines, that these are amongst the stages of IMS failure and that inadequate lubrication is a significant contributing factor.

What can we safely conclude about IMS ball bearings?

1. BALL BEARING IMS BEARINGS CAN WORK:
We know this because the vast majority of M96 and M97 engines do not suffer IMS failure. Many have gone well over 200,000 miles on their original bearings (both double-row and single-row) without suffering a failure. We must keep in mind the numbers released by Porsche and the fact that they are based upon hundreds of thousands of cars produced and up to 17 years of real-world use.

2. SOME SEALED FACTORY IMS BEARING DESIGNS ARE MUCH MORE RELIABLE/DURABLE THAN OTHERS:
- based upon the data obtained from Porsche during the discovery process in the class-action suit, the original dual-row bearings failed at a rate of much less than 1% regardless of mileage, use and maintenance schedules, whereas 8 to 10% of the original single row beaings failed.

3. CERAMIC BALL BEARINGS ARE MORE RELIABLE/DURABLE THAN STEEL BALL BEARINGS OF THE SAME DESIGN:
- As you indicate in reference to your own ceramic IMS bearing retrofit (and as confirmed by testing and years of experience in various applications), properly engineered ceramic ball bearings are more durable/reliable than properly engineered steel ones.

4. ALL BALL BEARINGS NEED ADEQUATE LUBRICATION:
Trite, of cousre, but important. Porsche erroneously chose not to lubricate their IMS ball bearings with oil, but relied upon a seal to keep the bearing packed in grease. As you highlight on your own site, as the seals start to fail on these bearings, sufficient oil is allowed in to wash out the grease, but insufficient to allow adequate lubrication of the bearing by oil. Ultimately, the result is failure of the bearing. Pedro echoes your observations in this thread when he says: "The oil that seeps into the IMS is not replenished and that's why (the bearing) is cooked."

5. THERE ARE TWO WAYS OF IMPROVING THE LUBRICATION TO THE BEARING:

The most simple of these is by removing the outer seal to the original IMS bearing - something which you and many others recommend as a stop-gap measure for those with the later, larger single-row bearing who cannot afford an engine tear-down in order to upgrade the bearing. Indeed, it is also why your (and Pedro's) ceramic retrofit bearings are unsealed. This method eliminates the grease and relies upon splash oil to lubricate the bearing. A question remains, however: is splash oil lubrication adequate in the long run, regardless of how the engine is used? There is insufficient data at this stage to answer that question definitively and, indeed, you recommend replacing your own ceramic bearings every 50,000 miles or 4 years.

The second method of improving the lubrication to the bearing is by DOF (direct oil feed), rather than splash lubrication. This is the method extolled by Pedro. Clearly it will provide much more oil and lubrication to the bearing under all driving/idling conditions than splash lubrication. Using it will undoubtedly eliminate the inadquate lubrication problem that you and others highlight as one of the stages of IMS failure.

Will DOF cause inadequate lubrication elsewhere in the engine? As we all know, oil pressure varies wtih oil viscosity, oil temperature, rpm's and engine wear. The M96 and M97 engines were designed and built to take this variation into account and there is no reason to believe that directing a small amount of oil to this bearing will reduce oil pressure elsewhere to a point of inadequate lubrication ( unless, of course, the engine is already suffering from low oil pressure). Indeed, you include direct oil lubrication to the bearing in your IMS Solution and must have come to the same conclusion.

Will DOF cause increased aeration and foaming in the oil that modern oils are incapable of coping with? Comparing the oil on the dipstick of a DOF equipped car versus a non-DOF equipped car after a hard run should go a long way towards answering this question. I, for one, encourage Pedro to produce a video checking the oil of two comparable cars (same vintage, mileage and with fresh oil of the same type) after comparable on-track drives. Common sense, IMO, also suggests that, after the initial start-up of a DOS system, air cannot enter the bearing housing as it is a sealed system: by definitioin, without air there cannot be aeration of the oil.

Is the IMS solution an upgrade over the original sealed IMS bearings? Undoubtedly. Is it also a significant upgrade over a properly lubricated, unsealed, ceramic ball bearing IMS bearing? Possibly - although in the case of dual-row bearing engines with upgraded ceramic bearings and improved lubrication, the 'solution' will have to be unbelievably durable to get better results over time.

Considering the cost, at this stage I still believe that using an LN ceramic bearing and splash lubrication is the way to go for most people - certainly for those with dual-row bearings. I am also inclined to believe that for the larger single-row bearing equipped cars (where the bearing cannot be upgraded without engine tear-down), removing the outer seal is an essential first step. However, for these engines, I believe that DOF is the way to go. Whatever theoretical risk there is of aeration should be overcome by dramatically reducing the known risk of IMS failure due to inadequate lubrication. Finally, with more evidence on the issue of aeration, I would also think that DOF and an upgraded bearing would be the most cost-effective fix for the remaining cars, rather than merely an upgraded bearing.

If money is no (or virtually no) object, then I would go with the LN Solution. History from Porsche's own non-ball bearing IMS cars has proven it to be a reliable component design that should all but eliminate the worry of IMS failure. If only the M96/M97 engines had been designed that way in the first place!

Brad






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[Jake Raby]

IMS bearing failures have dozens of contributing factors that we have discovered. There's probably just as many that we haven't discovered yet.

If we knew all about it, what I do wouldn't be called research.

[cnavarro]

Originally Posted by Jamesp

Jake,
Any idea of the typical run out on the IMS driven gear? I had the failed IMS from my engine measured at 0.015. Quite a bit for a gear, but as it is a chain drive if may be ok. In any event that was a major driver in replacing the damaged shaft with an undamaged one. My thought at the time was if the IMS gear run out was poorly controlled in the design, additional side loads could shorten bearing life in high run out cases even with a deep groove ball bearing.

This is one of our tests to qualify an IMS for our upgrade procedure. If the shaft has more than .005" of runout on the main sprocket, we fail it. Most shafts however don't have any. Only when the shaft has been subjected to an IMS failure or some other kind of trauma (broken chain), is it that we see runouts starting at .015" and only getting worse from there.

The other issue we check for is concentricity of the bearing housing bore as well as runout and taper. Most usually have a few tenths, but we've seen some that have several thousands when the sprocket has zero runout and in those cases, we will junk those shafts too. Unfortunately, this is all stuff you can't easily check for when the intermediate shaft is still in the car and specifically why carrying out a retrofit procedure on a bearing that has failed or is close to failure is not advised (excluding the foreign object debris that has already compromised the engine and will compromise the replacement bearing).