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Reduce IMS failures by eliminating shaft "pumping"

I know, the IMS bearing is the most overpopulated blog in Porsche history. However, Iím doing a full engine rebuild and have several ideas to reduce its failure rate without major reengineering or cost. Wanted to run these ideas past the community, and also Wayne Dempsey, for thoughts and feedback.

As a little bit of background, I have several mechanical engineering degrees from top 10 schools and practiced as an automotive engineer for almost a decade. I know more than average Joe when it comes to engineering design and root cause analysis, but also value field expertise. Iím doing a full engine rebuild of the 2001 Boxster S 6-sp with w/70k miles, all new parts are from Pelican.

I discovered a great thread on this topic in GrassRootsMechanic.com. https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/the-frugal-mechanic-meets-a-porsche-boxster/120457/page2/. Inside he (mrap1000) is suggesting to install an unsealed roller bearing and knocking a small pinhole on the other end of IMS next to the oil pump to promote minor oil flow through the IMS and then across the unsealed bearing. It sounds highly logical however one weakness may be that little to no oil flow will come through the end of the shaft next to the oil pump given the inherent design of the oil pump. With 200,000 boxers on the road globally, I suspect only one boxer has this design, so the sample size is just 1 and itís hard to assess the effectiveness of the fix. But I applaud him for his ingenuity an engineering prowess!!

Coupled the above, I couldnít help but notice that when I removed my I am IMS shaft bearing it was full of old oil. I wasnít unable to measure as it came out by surprise, but I suspect it was more than 50% full. Online I learned this is common for most IMS repairs.

One downside the design is the constant pressurization and vacuum that forms inside the intermediate shaft as the engine goes to heating and cooling cycles. Based on the well proven ideal gas law the pressure inside this intermediate shaft will increase approximately 6 psi from 70 degrees to 180 degrees (thermostat temp), and I suspect the actual shaft temperature is higher than 180 as it is at the very center of the engine, so conceivably the increasing pressure could be 7 to 8 PSI. While pressures donít seem very high, they are over 50% of the pressure of a normal football, and any small holes will absolutely allow air and oil leakage. As a consequence, every time the engine goes through a heat cycle youíre forcibly pumping oil through the IMS bearing and washing out the higher viscosity grease that the seals are designed to keep in the bearing. When the engine cools the shaft will create a vacuum and air and oil will come back into the shaft. After 100,000 miles the average engine has gone through 2000-5000 of these heat cycles. Thatís a lot of pumping across the bearing.

There are two simple ways to fix this heat cycle pumping action: 1) Fill the half shaft completely full oil before assembly thus removing all the air, or 2) Drill a small pinhole somewhere on the shaft to allow the air pressure to release without going through the bearing.

Pro/Cons of each:
Option 1. Fill shaft with oil.
PRO: Removes all the air. Also provides an oil bath on the backside of internal side of the bearing which will further cool the bearing from heat generated from rolling friction.
CON: The weight of the oil will create a slight pressure on the inside of the bearing and promote leakage path during non-operation. In other words, the oil will slowly seep out. When the oil leaks it will likely be replaced with air you are back to the same problem you started with (the pumping problem)Ö

Option 2. Drill small pinhole in shaft to release air pressure / vacuum during heat cycles.
PRO: Air is able to ďbreathĒ without passing through the bearing during heat cycles.
CON: The actual shaft could fail as they are a thin walled design and a small hole could lead to stress risers, cracks, and ultimately failures. Iíve done web search for known shaft failures but could not find any without bearing failures. However, there is so much bearing failure content online isolating just a shaft failure is a needle in a haystack exercise.

Here is the huge caveat. Neither fix can be accomplished with a normal IMS repair. This can only be accomplished during a full engine rebuild.

For option 1 and the oil fillÖ to fill the shaft with oil you must have the immediate shaft in a vertical position to fill up with oil. This means during engine rebuild with the shaft out, or with the engine removed and the entire engine stood vertically (not sure how to do this easily, engine stands do not rotate this direction). Or, if youíre really brave, stand the car on its front bumper during an IMS repair ;-) !!!

For option 2 and the drilled holeÖ. this is engine rebuild territory only, as you need drill the from the outside of the shaft. I suspect there may be a very small right-angle drill that could fit inside of shift thorough the bearing hole, but I have never seen one. (Maybe available in the orthopedics medical profession ??)

Iím a few weeks away from final assemble of my torn down engine. Will try to post pics later.

Many thanks to anyone who can share some engineering expertise on this subject.

(Sorry Wayne, not sure how we could monetize this solution!)


Old 04-15-2018, 11:26 AM
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The idea of punching a hole in the oil pump end of the shaft and using a roller bearing has already been "monetized" by more than one company offering retrofits. Problem with the idea is using a hammer and sharpened punch to put a correctly sized opening in the pump end is at best questionable, as is the need for a roller bearing, which has no better a load carrying capacity than a ceramic hybrid ball bearing unit, but the roller bearing is capable of generating more internal heat, which is not a good thing. The hole punch approach also requires an oil pump drive shaft with a notch ground into it for oil passage, which significantly weakens an already weak component.

As for controlling oil migration into the shaft, two solutions for that already exist: A hybrid ceramic ball bearing unit with no rear seal. but with a very good seal on the shaft side. Oiled by the mist inside the rear of the sump, oil does not enter the shaft. We have seen multiples of this design, which when removed from the shaft after tens of thousands of miles found no oil inside the shaft. Second approach is to insert a freeze type plug into the shaft before installation of the retrofit bearing, which totally seals the shaft from the bearing side. Works very well, and is also patented and commercially available, as is the ceramic hybrid with no rear seal.
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Old 04-15-2018, 11:54 AM
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Thx JFP, you seem to carry more expertise on the subject than I, by far.

I was reluctant to use the LN bearing. Way overpriced and they still recommend regular changes. The $800 part seems to be good basic engineering but still does not fix the root problem of the design and it is WAY overpriced. The $1700 better LN "solution" option is just stupid priced. I elected to try the PelicanParts $200 bearing and swap it out every 40k miles, and could put in a new clutch (for free) at the same time with the $600 savings vs LN. I spoke to PelicanParts sales and they have reported no failures to date with their solution.

Given what you know, with my engine in full teardown and I have the option to still go with any bearing option and/or oiling option, what do you recommend?

Last edited by Mike Petersen; 04-15-2018 at 12:22 PM..
Old 04-15-2018, 12:18 PM
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Quote:
Originally Posted by Mike Petersen View Post
Thx JFP, you seem to carry more expertise on the subject than I, by far.

I was reluctant to use the LN bearing. Way overpriced and they still recommend regular changes. The $800 part seems to be good basic engineering but still does not fix the root problem of the design and it is WAY overpriced. The $1700 better LN "solution" option is just stupid priced. I elected to try the PelicanParts $200 bearing and swap it out every 40k miles, and could put in a new clutch (for free) at the same time with the $600 savings vs LN. I spoke to PelicanParts sales and they have reported no failures to date with their solution.

Given what you know, with my engine in full teardown and I have the option to still go with any bearing option and/or oiling option, what do you recommend?
Without hesitation: The IMS Solution. It is the ONLY retrofit that is permanent, and can even be extracted and installed in another engine, which is why it costs more; it delivers more value than any other retrofit. No one has ever killed one, even when run for a short period without oil, which says a lot for the design. They are also a "plus" item when the car is sold.

We install a lot of them, and no one has ever expressed regret about them. Sometimes you do get what you paid for...........
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Old 04-15-2018, 12:51 PM
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$1700 is a big nut for a bearing. But I take your point...

Any thoughts on the poor-mans $0 solution that started the thread (option 1 or 2)? Hopefully much better than stock, but obviously not up to the LN Solution in reliability.

-Mike
Old 04-15-2018, 01:02 PM
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Quote:
Originally Posted by Mike Petersen View Post
$1700 is a big nut for a bearing. But I take your point...

Any thoughts on the poor-mans $0 solution that started the thread (option 1 or 2)? Hopefully much better than stock, but obviously not up to the LN Solution in reliability.

-Mike
I have no regard for Pelicans cheap update for two reasons: First, it is no better than what was already in the engine, which means it could just as easily fail at any time; second, they only offer a single row version which has to be used with a spacer in a dual row application. But the single row is the most prone to failure of the IMS designs. To me, it is simply false economy.

Drilling a hole in the shaft is a waste of time and could endanger the shaft. You want to keep oil out, use a good retrofit bearing like LN, or plug the shaft.

$1700 a big nut only until your factory bearing fails, then it was money well spent. The Solution is simply the best option available period.

And while you have the shaft out of the engine, you should either pin or weld the end gears in place as they have been known to slip...................
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Last edited by JFP in PA; 04-15-2018 at 02:13 PM..
Old 04-15-2018, 02:08 PM
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Thx for the opinion, JFP. Appreciated...
Old 04-15-2018, 02:12 PM
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JFP, I welded the IMS gears to the shaft and elected to purchase the IMS Solution. Will sleep better at night. Thx for the steer.
Old 05-31-2018, 07:39 PM
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