First post...why not make it about a potential IMS solution?

[ac74394]

Hello, Renntech!

 

This is my first post.  I am new to the Porsche community...proud new owner of a beautiful 2003 with roughly 70k miles!  It's always been a lifelong dream and I find myself thinking about my new silver bullet almost every waking moment!

 

Now, onto the topic of this thread...  I've been reading a bunch about the IMS bearing issues of M96 engines and have learned the following:

1. All the posts I have read have me scared crapless about the prospects of my new baby instantly turning into a paperweight due to a catastrophic engine failure
2. 'The IMS Solution', while seemingly very well designed, is way too expensive a fix for a seemingly simple problem
3. The 'IMS retrofit', while assuring due to the lower rate of failure, is also way too expensive to have to replace at clutch change intervals
4. The original Porsche solution can't possibly be so terribly engineered that a total redesign is necessary - perhaps a tweak is all that is needed (ball bearings are a sub-optimal solution to this challenge).

Everyone seems to agree that the reasons the IMS bearing typically fails is due to a lack of acceptable lubrication and a lack of bearing capacity.  Further, since the dual row versions have proven to fail at a rate substantially less than the single row version, we can conclude that IMS shaft angle misalignment is not a typical contributing factor (i.e., due to the fact that dual row bearings are less tolerant to misalignment than single row).  Lastly, most specialists seem to be of the camp that crankcase oil is of sufficient abundance and quality to keep a properly engineered bearing properly lubricated. 

 

Therefore, when distilling the IMS bearing issue down to the essence, there seems to be an issue of axial load and radial load.  I again, without empirical evidence to prove my thoughts, think that when Porsche originally engineered the IMS bearing design, they miscalculated the impact of axial load's contribution to the bearing's overall load.

 

To get to the point, has anyone contemplated a tapered roller bearing as a part of an IMS retrofit solution?  For example, NTN 4T 30204 seems to be a drop-in replacement for the single row IMS bearing spec.  Regarding lubrication, typically roller bearings require more lubricity and heat dissipation (a byproduct of being able to handle much larger loads).  If a force feed is needed, why wouldn't it be possible to tap a fitting into the original IMS flange and scavenge oil from one of the galleys?

 

I know this is a fairly heavy topic for my first post but I dislike challenges and I like solutions where everyone can win...especially as the value of these cars will likely benefit from a great solution!

 

Contributions are welcome and flaming is not.

 

Angelo

 

[JFP in PA]

Welcome to RennTech :welcome:

This is a topic that gets re-chewed periodically.  The people that developed the IMS retrofit tried a wide variety of different bearing designs and materials of construction before settling on the current ceramic hybrid design.  Based upon size constraints of the case opening and the inside of the existing shaft, I don't think a conical bearing would be practical for a couple of reasons as you would need an internal race inside the shaft, which would limit the size of the bearing rollers.  Drilling into the existing IMS flange would also present issues as it is not very thick and putting a hole in it could weaken it significantly. If you look at the flanges used on oil fed designs, they have increased thickness to accommodate the oil lines without creating problems.  Because of the proximity of the flywheel to the engine cases, you cannot realistically tap into oil inside the bell housing, so you need to go to the outside.  The rather well thought out design used in the IMS Solution (tapping into a spin on filter adaptor to get freshly filtered oil) is out as it is patented; tapping into the oil in the cylinder heads has created issues with the VarioCam systems, plus it sources oil from one of the hottest and dirtiest parts of the engine.

 

While potentially possible, I think the use of a conical bearing would need a lot of costly development work before it was practical, which would be difficult to recoup as there are existing products already on the market that are doing an excellent job (there are nearly 20K LN retrofits running around on the street).

[ac74394]

JFP in PA, thanks for your warm welcome!  And thanks for your thoughts.  I've read many of your posts and was hoping you would join in on the discussion!

 

Again, I think the LN retrofits are a good band aid to the M96 (single bearing design) IMS problem but I also think the notion of a part which was never intended to be serviced being replaced with a part that has a prescribed service interval could be improved upon.  

 

NTN 4T 30204 is a tapered bearing design that appears to be a drop in replacement to the single row IMS bearing (dimensions measure out to 20x47x14).  This bearing has far greater axial and radial load bearing capability vs. the OE IMS bearing and probably LN's sourced hybrid single row as well.

 

With respect to the oil scavenging, I agree that oil is hottest at the heads but I do not agree with the argument that the oil is dirtiest when scavenging at the heads for simple reason that oil in the galley is not recycled.  The galleys are pressurized.  Any oil fed to bearing surfaces is expelled from the bearing, and drained to the sump.  Regarding heat, I wouldn't think it excessive at the head to compromise a bearing.  Anyway,  any flexible hose used to scavenge would certainly drop the oil temp a few degrees by the time it is introduced to the IMS region.

 

Regarding the notion of tapping into the IMS flange, I contemplated the thought that structural integrity could be compromised.  While I think it's an unlikely scenario, it wouldn't be very difficult to have a part of the flange built up to create a suitably reinforced portion in which to tap a very small AN fitting.  Also, I think a fitting would be self-reinforcing due to the load being pulled in toward the engine block.   Tapping into the IMS flange could be done with a male to male fitting coupled with a 90 degree elbow, going out the same way as 'The IMS Solution' and the 'DOF' solution - I'm unsure clearance would be a problem as it is not for the other solutions.

 

Again, I can't help but think the Porsche engineers largely knew what they were doing when they designed the M96 engine...and that a permanent solution is close at hand!

 

That said, if consensus is that the current solutions are adequate for the need then I'll bite the bullet and join the crowd....

[j_beede]

Hello Angelo,

Thanks for sharing your thoughts regarding the IMSB. With all due respect to Timken, I would jump at the chance to replace my IMSB with Raby's "solution"... if I knew that my 997 had the smaller diameter, "serviceable" IMSB. I would prefer a properly lubricated plain bearing to any roller bearing variant.

 

Regarding your learnings...

• All the posts I have read have me scared crapless about the prospects of my new baby instantly turning into a paperweight due to a catastrophic engine failure. Unfortunately too many 996 and 997 owner's have experienced the "paperweight" syndrome. It happens. An acquaintance had his lovely 996 C2 coast to a stop while cruising at 80MPH on I-80. He knew he was in trouble when he opened the door and the pool of oil was already visible from the driver's seat. The local p-car dealer offered him $750 for the remains "because it had nice wheels and tires". Out of kindness I suppose.
• 'The IMS Solution', while seemingly very well designed, is way too expensive a fix for a seemingly simple problem. I suppose expensive is a relative term. To someone with the newer, larger IMSB the "Solution" is a downright cheap fix!
• The 'IMS retrofit', while assuring due to the lower rate of failure, is also way too expensive to have to replace at clutch change intervals
• The original Porsche solution can't possibly be so terribly engineered that a total redesign is necessary - perhaps a tweak is all that is needed (ball bearings are a sub-optimal solution to this challenge). Two things here... 1) I believe the original/previous IMS implementations (pre-996) used a plain bearing. 2) I was told by an engine builder that the IMS system was commissioned by Porsche and designed well east of Stuttgart. Anyone Porsche historians know the true story? I think the value proposition for the LN and Raby work is enhanced by the fact that they are retrofits, not total redesigns.

Edited June 15, 2015 by j_beede