"remember Porsche themselves read a bearing catalogue and look where that got them! "
Probably the Product Costing Dept. choice, not the Product Engineering Dept.
Just read the Boca bearing thread linked above

Hi 78F350,

for shure you can replace the center bolt if you want. My point was how to remove it if you want to reuse it. And if the one in the car is worn or the IMSB is worn, there is no other way as to replace it. The OEM one wasn't designed to be removed in the way it is done by pulling the IMSB with it and than reuse it. That was my point.

Another point is material quality, rigidity, durability, expansion. Maybe the replacement looks better, but that always does mean it is better. Shure, the after market manufacturers will know what they do, but bigger doesn''t always mean better. It has to fit the conditions and than has to be made better.

Regards, Markus

Jake was one of the first to do IMS bearing replacements at a time when Porsche said it could not be done. He was involved in testing some of the designs that eventually evolved into what we now know as LN bearing kits, tools and directions. He has done thousands of replacements I'd wager.

Knowledge improves over time (witness the engines Jake blew up testing before they got it right and were ready with a product you could buy, witness the changes in one of the LN products between initial availability and today). Having a high quantity of samples and a "please return" policy also improves the insight into needed design changes. It also gives forum readers insight into what may be working and what isn't. Statistics are meaningful.

But in the end, it is your car, your money, your decision. Come back in 5 years and tell us how it all worked for you keeping in mind even that much quantity one usage means little when assessing product quality and suitability.

(That my single and double row experiences were without failure is meaningless in the path to determining product reliability. Too small a sample. To reveal my bias for quantity testing, I come from a background where millions of test cycles were a minimum.)

I have great faith an SKF's testing methodology. My challenge is to make sure that the bearing has conditions that are acceptable. I think the best way to do that is with a freeze plug. Preventing oil from washing out the bearing will enable me to get the SKF rated service like from my chosen bearing.

I am definitely going out on a limb, at least as far as the Porsche community is concerned. You're right, Time will tell.

As to the cautionary tale of KK, he was trying to use a cheaper bearing with inferior ratings to do the job. I am trying to use a top notch bearing with exceptional ratings to do a hopefully better job than what is currently available on the market.

Absolutely without pioneers I would not be in a position where I could take this experiment and have any minimal chance of success. The work of others has put me in a position where I can possibly even incrementally improve the IMS situation.

What I want is a lifetime solution, and I'm going to do my darndest to get as close to that as humanly possible.

And, I reserve the right to cancel my experiment and go with a proven quantity if that is what I determine to be the best course of action. So far my plan still looks good, but I'm always open to being proven incorrect.

Regards,

Silber

The IMS Solution is the closest you'll get to a 'lifetime solution' It's just that simple.

It's not that simple and there is exactly zero data to back that up. Plain bearings are not permanent and do wear/fail. It's just a fact. That's why you replace them when rebuilding an engine. ;)

Until many have been pulled and measured for wear after 50k, 75k, 100k miles, and until many of them have done years of service without failure, it's all just guessing and marketing hype.

I would trust it more than a single row ball bearing, but the price is ridiculous.
I'm glad I have a dual row that will only be replaced with the same. :)

KK used a Ceramic Hybrid bearing and removed both seals.That bearing is more 'expensive' than the usual $3 steel bearing, not cheaper.
Nothing wrong with the bearing spec but it failed in his engine.
https://rennlist.com/forums/996-forum/750825-different-approach-to-diy-imsb-retro-parts-and-pics.html

"As to the cautionary tale of KK, he was trying to use a cheaper bearing with inferior ratings to do the job."

I'm thinking it may be beneficial to post some of my thoughts about this, so if you don't like rambling skip this post.

Porsche had some of the best engineers in the world designing this engine. They looked at the numbers for the bearings, and their load data, and came up with their bearing being a lifetime solution. These were smart guys, they didn't just go to a bearing catalog and pick something at random.

But, obviously, they made some sort of mistake or we wouldn't see the failure rates we do. What was their mistake? I think it was the open tube inside the IMS shaft. Thing is, that tube acts like a small lung. Every time your car heats up, the air inside it expands and it "exhales" through the seals of the IMS bearing. Then when you stop your car and it cools it "inhales" oil from the sump through the IMS bearing seals and into the IMS tube as it cools and the air contracts.

So, I think the enemy of the IMS bearing is heat cycles. Every time the car heats up and cools down, a little bit of grease gets washed out of the bearing. Does evidence support my theory? The bearings have the grease washed out, the IMS tube is usually full of oil. At least some evidence exists. Sealed bearings running in an oily environment don't normally wash out as bad as these IMS bearings do, by a long shot. Reading some Machining forums sealed bearings in oil is fairly common and not problematic.

So, I think the Porsche engineers got it right, in that the bearings they specified, if kept intact, will work as long as they thought. They did not predict the lung effect.

I think the lung effect can be countered by plugging the IMS shaft tube with a freeze plug. Your lung will go from the size of a small dog's lung, to the size of a gerbil's. Not near as much, if any, oil will get pulled through the bearing. This allows the 2rs seals to do their job of keeping the grease intact and allowing the bearing to live to its rated service life.

Is this theory a good one? I think so. The bearing washout and oil getting into the IMS tube in the quantities it does has to be explained somehow. Will my solution (2rs + Freeze plug) actually work? I think so, but you are all right, it has to be proven, as unproven it is nothing more than ramblings of an internet nobody.

Silber

I looked up the bearing he used. From what I can tell, it was a $60 or so ceramic hybrid bearing, where the SKF hybrid is $150. It was a cheap hybrid, maybe price wise above a steel bearing, but effectively you would be worse off with that bearing as compared to an SKF steel one. Fatigue limits for his bearing were very poor, not a bearing suited for an engine.

Silber

I hate reading Rennlist because there is so much cr@p to wade thru to find any content. What I did find from the links Gelbster posted was that the spec of the bearing, as Silber just said, was a 'light duty' bearing which had no place being used in an engine. 6204 spec. If what I read is correct.
Another interesting bit was the mention of counterfeit/sub-spec NSK bearings possibly being used by Porsche.

Edit: Looking further into the bearing info (I know nothing about bearings) It looks like the post on Rennlist wasn't exactly correct about the numbers in the bearing code, unless I misread.
This was a good chart to look over: http://www.kykbrg.com/KYK%20pdf/Bearing%20Classification.pdf
My take-away is that Personally, I should leave bearing selection to others.

There is way more to this subject than the merely the specs of the bearing or discussing load vs lube.This is just conventional M96 wisdom.I am not an expert . 6204 & 5204 are just a dimension code. the Abec rating is a useful spec but C3 seems adequate.Tight clearances like 5+ may be a disadvantage ? then there is cage, seal, hybrids etc.
M96 engines may have different IMSB-related defects and to varying degrees. So are we discussing a better spec for a specific engine, a specific tye of bearing/year model or a panacea for all M96 ?
Let's exclude the collateral/ FOM damage failures because they are unrelated to IMSB specs.

Until you know the IMS-related defects(if any) in a specific engine ,how will you propose a solution for that engine ? And how does that spec apply to all M96 ?
For example -if Runout of the tube and/or sproket is the problem, tweaking ball bearing specs won't fix it. A plain bearing or a roller bearing might up to a limit . But what runout limit ?
If there are no IMS related defects in an engine , a1RS $3 OEM-spec bearing would probably be O.K. - particularly if the original bearing did not fail even after 100k miles. In such a case a superior spec bearing could be installed and after another 100k miles it would also be in good condition. Which would prove what about "better" bearing specs.?
Perhaps the best justification for using a "better" spec is that the upgrade costs little and does no harm - as long as you remove only 1 seal. 1RS seals do not seem to fail.Why?
The wisdom of using a plug in the IMS tube like "The Solution: has been reviewed and dismissed in previous discussions. For deep groove ball bearings and roller bearings 1RS works well in thousands of applications, so what additional benefits would the IMS Tube plug offer?
Note that seal failure often precedes IMSB failure. In which case, the primary cause of failure is seal spec/placement not bearing spec.
After years of participating in such discussions I have learned how much I/we do not know about this subject and just follow what works for people who install or warranty hundreds or even thousand of these bearings.Some of them still try to help in these Threads but it is futile.

But what about the Installation or Pre-Qualification ?
For example - CH bearings are brittle compared to steel and therefore vulnerable to Installation mistakes.
Maybe the CH bearing was also knock-off like some NSK reputedly may have been ? - There is way more to this than just bearing specs.

Hi,

i'd like to summarize some things.

The IMSB specs are important. Especially the technical specs of the bearing itself. Same size and type doesn't mean same technical specs.

If you remove a seal from a sealed IMSB you just have no specs, because the bearing wasn't designed and tested for that by the manufacturer.

If you have a damaged IMSB, you need to do much more than just to replace it and the risk that your engine might fail is very very high.

The lung effect (as Silber called it) is for shure problem. And no tiny IMSB seal will handle that. So there were many attempts to solve the problem. DOF and open bearings and so on. In the end the plain bearing might be a solution, but at a price point where i just say no, because there are also other engine parts that can fail, so no win.

The IMSB is one thing, but the other more important thing (compared to a better spec IMSB than the OEM one) is the proper deinstallation of the IMSB and parts related, so the IMS doesn't get damage in any way and also the proper installation of the new IMSB and all the parts related. I think that topic is often underrated, but it's very easy to harm an IMSB or IMS when you install or deinstall.

My personal conclusion: i have a manual transmission. I need a new clutch around every 100 K Km (approx 66 K miles). I do an IMSB change every time i do the clutch. I do a yearly oil change, even if i drive much less than 5 K Km (3 K miles) a year. And if the engine or ISMB fails, it fails.

Regards, Markus

PS: SIlber: i think you have the right approach, but i wouldn't insist on looking for a "lifetime" solution.

Welcome back Markus. Your wisdom and perspective were missed.
Speaking of wisdom - perhaps we both need to abandon Threads long before we get exasperated with repetition ?
Another good example is the 6 speed transmission oil spec ! :-)
Your contribution to that subject was also invaluable but often ignored

In the UK there is a well known engine builder (amongst other things) that do use an updated or updated IMS shaft as part of their rebuilds.

Just bought two of these:

http://www.jegs.com/i/Dorman/326/565-104.1/10002/-1?CAWELAID=230006180037518699&CAGPSPN=pla&CAAGID=4 4693592161&CATCI=aud-194567928791:pla-182821358711&CATARGETID=230006180039216703&cadevic e=c&gclid=EAIaIQobChMImbyXnvqk1QIVRpd-Ch3EmAVREAYYASABEgL5LvD_BwE

I went with brass for two reasons:

1) it is softer so less likely to damage IMS shaft on insertion.

2) It expands at a slightly higher rate than steel, so this will keep it snug when the engine heats up.

Only need one, got a spare just in case. Will measure when they get here to see if one will fit properly.

Silber

Do you mean to say Hartech?
I have the hard copy of the Magnum Opus by Baz.
https://www.hartech.org/images/downloads/Hartech%20Engine%20Guide%20(interim).pdf
this is fun:
https://www.hartech.org/hartech-videos

Hello Silber,

some thoughts on the plug idea:
Make shure it can't move.
Make shure it doesn't put too much pressure on the IMS tube and that the pressure is evenly.
Make shure it doesn't influence the balancing of the IMS tube.
Make shure it is removable – just in case.

Also i would calculate the possible pressure differences, just to get an idea what differences you have to handle.

This is why i would rethink the idea and would come up with a more sophisticated plug. OK, i'm a native german guy. ;)

Also study the OEM main bolt and the IMSB. There was the idea that both together create a seal towards the IMS tube that is more sealing than the IMSB seal itself.

Regards, Markus

Yes, everything fails in time, but if you read closely Silber's goal, he's looking for the solution that will last the longest. From the known data of ISMB replacements, the LN single row and double row replacements have the fewest failures. While the IMS Solution has sold fewer units and less actual data, there are no reported failures. It information such as this that leads to informed decision in light of imperfect data. That's not guessing nor is it marketing hype. To say so is disingenuous.

That's a bold statement, though. I don't believe that they have a lower incidence of failure as there is no data to back that up. I require numbers from independent sources. When you're getting all of your information (not data) from the seller of the product or their affiliates, that information must be met with a degree of skepticism.

It's all guessing and marketing hype. :)

Yes I do mean Hartech.

Hello Silber,

concerning the SKF 6204 2RSLTN9 hybrid bearing. Please read the recommendations from SKF for that bearing.

Sorry i coudn''t find an english version of that product catalogue: Medienbibliothek

Read chapter 15F Hybridlager

This bearing series is designes for electric motors. Not shure if this bearing is really recommendable for an IMSB application.

Regards, Markus

Brilliant research Markus.
The CH does nothing to solve the seal issue nor the out of round,nor the run out problems that bedevil the generic deep groove ball bearing for IMSB.
The surprising success of the modified roller bearing for IMSB may be that it is more tolerant of slight alignment problems.
If the original bearing has survived 100K miles, a generic 1RS $3 bearing would probably perform just as well. It would be more tolerant of clumsy Installation.
But without the results of a Pre-Qualification Inspection much of this chatter is meaningless.......
Anyway, it is easy to replace the IMSB whenever you replace the clutch (per Markus). So ultimate life span is a curious goal.
Minimizing the risk of premature failure with a more fault tolerant design - now that may be a more useful goal in the M96 real world. That is what an oil fed, plain bearing with all kinds of modifications achieves - at a price. But only if the engine passes Pre-Qualification.

Hello,

this might chart be also helpful. It shows the specs and abbreviations for SKF bearings. Sorry, i have it only in german language. But it may help and also it might show that there are more things to consider than width, height and rpm. ;)

@ Gelbster: i think the main problem is that this specific SKF 6204 2RSLTN9 bearing wasn't designed for an application in an engine oil bath. It was designed for a dry environment as a electric motor bearing. Also it isn't very heat resistant. For example it is not allowed to be heated up over 80 degrees celsius (176 degree fahrenheit) when you install it. No problem when you install it as an ISMB, because you have to cool it down, but it shows that it is not very heat resistant. In an inner engine enviroment you can have 150 degrees celsius (300 degree fahrenheit) very easily.

Regards, Markus

This is where i got my temperature data:

Temperature limits

If it turns out the skf bearing is a no-go thats OK. If my analysis of the root cause is good, the pelican bearing shouldbe just fine with a freeze plug behind it to stop grease washout.

Silber

Hello,

for those that are interested in i found the english version of the SKF bearing catalogue. Lots of infos:
Library

Overview of all 6204 SKF bearings available:
SearchResult

And this might be interesting for all that want to go deeper in this topic:
SearchResult

@ Silber: think the pelican bearing is OK for shure. Most important part is very careful de- / installation.

@ Gelbster: I recommend to read the introduction of the SKF catalogue about what types of bearings are available and what are the differences in detail. Chapter A to H. I'm pretty shure you'll find some interesting facts. ;)

Regards, Markus

Sorry, double posting.

The freeze plug & grease washout.I don't understand.
The fundamental problem is that conventional IMSB wisdom suggests the bearing seals deteriorate because of heat.(BTW, the same problem affects a similar bearing in the 6 speed gearbox.) Then the grease washes out because the bearing is partially(1/3) immersed in engine oil.
How will a freeze plug solve the heat deterioration problem for the bearing seals ?
If you fit a Freeze plug and remove one or both seals, that is different.
If you remove both seals ,the logic of a freeze plug is obvious.You avoid partial filling the IMS tube with oil
If you remove just the outer seal, the freeze plug seems unnecessary.
So what does the freeze plug achieve exactly and with which seals remaining/removed?
Assuming it is a good interference fit & doesn't distort the tube during install.

I think there are more parameters than seal deterioration.

Type of bearing and capability to handle axial force, torsion and vibrations.
Type of cage.
Type of grease if you have a sealed one - heat resistancy.
Type of sealing and seal material.
Misalignment IMS and ISMB.
Rotation Per Minute / Friction inside the IMSB.
Amount of contamination the IMSB can handle. hc
Heat and heat cycles.
Maybe fast up and downcycling when motor revs up or down.

And again. If you have a bearing that was designed to run as a sealed bearing and you remove the sealing, you have no specification, because the bearing wasn't designed for that.

There are bearings that are designed to run in oil. These might be the right choice if you want to run an open bearing,

Regards, Markus

I am not sure this is entirely right, I think the main problem is the heat cycles of the air in the IMS tube sucking oil past the seals. I am trying to solve that issue.

So, I am correcting the problem I think to be the root cause of the issue. I can see heat deteriorating the seals to some degree, perhaps a bearing with Viton seals would be ideal. If heat deterioration was the only issue, why would the oil run into the IMS tube, but not come back out?

I am leaning toward the pelican bearing with the freeze plug rather than a fancy ceramic bearing, not sure if I really believe ceramic is needed at this point especially if I change them every time I change the clutch. Standard 6204's are around US $6-10 each. Porsche thought they were a lifetime solution and if I can fix the oil ingress issue, I can probably make 75k miles or so.

Silber

P.S. - Here was where I explain my theory http://986forum.com/forums/545188-post48.html

Great points Markus, I answer below :)

Freeze plug is designed to hold back heated engine coolant at a high pressure, should be more than up to this task.

The place where it will be driven into IMS tube is at the very most supported point in the entire IMS assembly. Deep inside all the reinforcement around the sprocket. It can push against that casting, same as the bearing just with a tube in between.
It is a very lightweight and symmetrical part, I am not worried of this.
.
Freeze plugs are removeable HOWEVER I would not use a freeze plug with anything other than an uprated center bolt. If the center bolt fails you will have to drive the freeze plug deep into the shaft to remove the broken bolt OR come up with a way to pull via the stub of the original broken bolt.

With an uprated center bolt, I cannot see it snapping when you pull, so not really a concern.

Rather than calculating pressures, I am trying to source a damaged Intermediate shaft to plug, and then put an air pressure gauge onto, then just stick it in an oven at 300f and see what we get.

regards,

Silber

Hello Silber,

there are 3 different types of IMS for the 986 available - depends on bearing and engine type. Make shure you get the right one for you car, because there are differences.

Regards, Markus

Markus,

I am just planning to plug the end of the spare IMS and test how much pressure is generated by heating it up. Will not actually be installed on my car, so doesn't really matter which version it is.

Steve

Thought I would update this thread with what I finally decided to do.

Since I ultimately decided to prepare my car to SCCA STR class rules, I am only allowed to put in the part that is either the Porsche original part, or the most closely similar available part. Since Porsche does not offer an IMS bearing separately, the most similar part available that I could find was the pelican parts IMS kit. Any other part would likely get me protested and I would lose.

If I had not been preparing to autocross class rules I would’ve put in a freeze plug, but since I am that is not an option.

Regards,

Silber