The Dreaded IMSB

User avatar
5chn3ll
Six shots...or only five?
Posts: 4640
Joined: Fri Jan 05, 2018 4:35 pm

The Dreaded IMSB

Post by 5chn3ll » Sat Jan 06, 2018 1:07 pm

The Dreaded IMSB is the Bitcoin of automotive flaws: everyone knows it exists, and about .01% of the population can effectively articulate exactly why you should care.

Here's the 996Outpost.com Not-Very-Technical Technical Brief, Intermediate Shaft Bearing edition.

The intermediate shaft bearing (hereafter IMSB) supports one end of the lay shaft, a cylindrical component crucial for engine timing. In older 911's, the intermediate shaft is supported on both ends by an oil-fed, plain bearing. The 996 introduced a new type of engine case that does not have a source of clean, pressurized oil to feed the "back" (toward the front of the car in a 996) end of the intermediate shaft...so a sealed steel ball bearing was used instead. For reasons that are hotly contested but ultimately don't make a damn bit of difference, those ball bearings fail.

Which cars are safe? Which aren't safe? Are any immune?
Mostly safe: The oldest 996's - those built in and before 1999 and a few after - were equipped with a fairly robust dual-row bearing. This was replaced with a single-row bearing; this is the culprit being the vast majority of IMSB-related engine failures.
Least safe: The next batch of engines, which covers an array of years from 2000ish through 2005. This is ALL water-cooled normally-aspirated 911 engines: Carrera, Carrera 4, Carrera 4S.
Most safe: In 2006, a larger single-row bearing was introduced. This is the first factory bearing since the early dual-row bearings that are generally considered safe.
Immune: All turbocharged 996's, as well as the track variant naturally aspirated engines (GT3, GT3RS) are immune from intermediate shaft bearing failure.

Oh, s**tballs! WHAT AM I GONNA DO?
Yeah, we all go through this phase of self-defecation after picking up that impossibly affordable 996. Another fine mess I've gotten myself into...what to do?

There are options. COUNTLESS options. I'm going to list the ones I like in the order I like 'em. If anyone else ever signs up, they can bitch and argue below. :D

There are a few scenarios; here's how I'd handle each of them in order of risk tolerance - least risk last.

* My "new" 911 is a very early car with the original engine: Do nothing, install dual-row classic IMSB retrofit, install IMS Solution.
* My "new" 911 is 2000-2005, or an earlier car with a replaced engine that has the '00-'05 bearing: install dual-row pro IMSB retrofit, install IMS Solution.
* My "new" 911 is 2006+: Do nothing, be content with the knowledge that your bearing sucks a lot less than many, many others.

In addition to the LN Engineering retrofit kits, Pelican Parts, European Parts Solutions, and others sell bearing kits. Opinions vary vastly.

Ultimately, what you do is based on your tolerance for risk and your willingness to spend money preventively. If you got into your 996 for next to nothing and you plan to rag it out until it dies, spend that bearing money on a nice underglow kit instead. If you bought your 996 because you realized that you can buy a 90's-vintage supercar (yeah, back in the 90's, supercars were slower) for Corolla money, and you really, really prefer to drive it rather than look at it wistfully and remember fondly what it was like to drive, address the issue.

Understeer: You will hit the wall with the front end.
Oversteer: You will hit the wall with the rear end.
Horsepower: How hard you will hit the wall.
Torque: How far you will move the wall.

Gone hunting with Alec Baldwin and Dick Cheney. Back soon.

User avatar
32wildbilly
Never gonna run around and desert you
Posts: 5758
Joined: Sat Jan 06, 2018 2:46 pm
Location: Kneebraska

Re: The Dreaded IMSB

Post by 32wildbilly » Sun Jan 07, 2018 11:46 am

...or this...2005 C4S that I did not buy cheap. 54k miles. Toy not a beater. Had no idea of IMSB prior to purchase. Joined the forums. Read. Panicked and didn't drive much first year or so while my mind processed the flood of conflicting information. Have come to the realization it will probably score or oval the cylinder liners even if I change the IMSB. I now drive it when I want and if my IMSB chows out I will replace engine with an RND product. After all percentage of failure depending on who you believe is in the 8% range or so...

..."Livin on the edge"...Hell, yeah!
Never gonna make you cry...

User avatar
B-ran
OG (First 100 Outposters!)
Posts: 76
Joined: Thu Jan 18, 2018 7:22 am
Location: Milwaukee

Re: The Dreaded IMSB

Post by B-ran » Thu Jan 18, 2018 12:51 pm

I have found that putting some red tape over that pesky “IMSB Detonate” button in the cabin has helped extend the life of my car at least the last thirty some thousand miles I have put on her in the last 15 months. But some days I am sleep deprived and loopy on my commute, so I may accidentally press that button....
99 C2 Aero that had its fried eggs surgically removed by a previous owner.

User avatar
5chn3ll
Six shots...or only five?
Posts: 4640
Joined: Fri Jan 05, 2018 4:35 pm

Re: The Dreaded IMSB

Post by 5chn3ll » Tue Jan 23, 2018 11:27 am

This information is part of the discovery materials from the class-action suit. The info is dated, but it illustrates the IMSB failure differences between model years.

"Discovery and investigation establishes that Porsche adopted a single row design for the IMS in 2001. The payment of warranty and goodwill claims of owners of Porsche vehicles with this design of the IMS (all Class Vehicles) spiked up to between 4% to 8% of all such Vehicles in the United States, and 4% to 10% of all Class Vehicles in California. Warranty claims for Porsche Boxster and 911 vehicles relating to IMS issues, which had different versions of the IMS, have uniformly involved claims of far less than 1 % of such vehicles. Indeed, to date, Porsche has spent over $20,000,000 reimbursing customers for the parts and labor necessary to repair vehicles experiencing engine damage or failure as a result of the defective IMS shaft. (This entails approximately 3,100 claims granted under warranty or good will.)"

One crucial point that bears repeating is that the IMSB fails over time. Every percentage/stat you see about IMSB failure rates represent a snapshot of reality at a specific moment in time. You'll see people throwing out numbers suggesting that 10% of 996's are susceptible to IMSB failure, which suggests that 90% are not. In reality, ALL intermediate shaft bearings will eventually fail, just like any other mechanical part. In fact, every part in your engine has a 100% chance of eventual failure.

The goal/point of preventive maintenance is identifying the parts that are more prone to failure (or parts that cause the most collateral damage when they fail) and getting those parts on a replacement schedule so you can keep ahead of failures.

Understeer: You will hit the wall with the front end.
Oversteer: You will hit the wall with the rear end.
Horsepower: How hard you will hit the wall.
Torque: How far you will move the wall.

Gone hunting with Alec Baldwin and Dick Cheney. Back soon.

User avatar
32wildbilly
Never gonna run around and desert you
Posts: 5758
Joined: Sat Jan 06, 2018 2:46 pm
Location: Kneebraska

Re: The Dreaded IMSB

Post by 32wildbilly » Wed Jan 24, 2018 1:12 pm

ElSchnell wrote: Tue Jan 23, 2018 11:27 am This information is part of the discovery materials from the class-action suit. The info is dated, but it illustrates the IMSB failure differences between model years.

"Discovery and investigation establishes that Porsche adopted a single row design for the IMS in 2001. The payment of warranty and goodwill claims of owners of Porsche vehicles with this design of the IMS (all Class Vehicles) spiked up to between 4% to 8% of all such Vehicles in the United States, and 4% to 10% of all Class Vehicles in California. Warranty claims for Porsche Boxster and 911 vehicles relating to IMS issues, which had different versions of the IMS, have uniformly involved claims of far less than 1 % of such vehicles. Indeed, to date, Porsche has spent over $20,000,000 reimbursing customers for the parts and labor necessary to repair vehicles experiencing engine damage or failure as a result of the defective IMS shaft. (This entails approximately 3,100 claims granted under warranty or good will.)"

One crucial point that bears repeating is that the IMSB fails over time. Every percentage/stat you see about IMSB failure rates represent a snapshot of reality at a specific moment in time. You'll see people throwing out numbers suggesting that 10% of 996's are susceptible to IMSB failure, which suggests that 90% are not. In reality, ALL intermediate shaft bearings will eventually fail, just like any other mechanical part. In fact, every part in your engine has a 100% chance of eventual failure.

The goal/point of preventive maintenance is identifying the parts that are more prone to failure (or parts that cause the most collateral damage when they fail) and getting those parts on a replacement schedule so you can keep ahead of failures.
HHHMMM...excellent points. Kind of like not changing the timing belt on overhead cam engines is stupid. HHHMMM I must rethink this cavalier attitude!
Never gonna make you cry...

User avatar
5chn3ll
Six shots...or only five?
Posts: 4640
Joined: Fri Jan 05, 2018 4:35 pm

Re: The Dreaded IMSB

Post by 5chn3ll » Thu Jan 25, 2018 8:18 am

There appears to be some confusion about the sound a failing bearing makes. The popular analogy is that it sounds like a "can of marbles," NOT a "can of marble" as you often see online. If your 996 sounds like this when it's running, you have a different issue.
147447463191073p.jpg
147447463191073p.jpg (100.82 KiB) Viewed 3877 times

Understeer: You will hit the wall with the front end.
Oversteer: You will hit the wall with the rear end.
Horsepower: How hard you will hit the wall.
Torque: How far you will move the wall.

Gone hunting with Alec Baldwin and Dick Cheney. Back soon.

User avatar
32wildbilly
Never gonna run around and desert you
Posts: 5758
Joined: Sat Jan 06, 2018 2:46 pm
Location: Kneebraska

Re: The Dreaded IMSB

Post by 32wildbilly » Thu Jan 25, 2018 2:41 pm

What kind of websites do you shop at that has marble trash cans for sale??
Never gonna make you cry...

User avatar
gnat
Power-drunk moderator
Posts: 4171
Joined: Sat Jan 06, 2018 6:54 am
Location: Lobby, VWGofA HQ

Re: The Dreaded IMSB

Post by gnat » Thu Jan 25, 2018 5:26 pm

32wildbilly wrote: Thu Jan 25, 2018 2:41 pm What kind of websites do you shop at that has marble trash cans for sale??
The kind where you need a golden IMSB to get through the door.

Speaking of, my empirical study of the IMSB problem shows that 100% of gold plated IMSBs fail to fail.

User avatar
5chn3ll
Six shots...or only five?
Posts: 4640
Joined: Fri Jan 05, 2018 4:35 pm

Re: The Dreaded IMSB

Post by 5chn3ll » Fri Jan 26, 2018 11:17 am

Even if you're a tool and wind up "cleaning" most of the gold off of said IMSB?

Understeer: You will hit the wall with the front end.
Oversteer: You will hit the wall with the rear end.
Horsepower: How hard you will hit the wall.
Torque: How far you will move the wall.

Gone hunting with Alec Baldwin and Dick Cheney. Back soon.

User avatar
OceanBlue2000
Fresh out of funny, ask Frunk
Posts: 674
Joined: Mon Jan 22, 2018 6:01 am
Location: Swamps o' Jersey

Re: The Dreaded IMSB

Post by OceanBlue2000 » Tue Jan 30, 2018 10:32 am

I've got a sort of relevant question. I am two years (and tens of thousands of miles) away from the time limit on my LNE bearing. Has anyone had the bearing installed long enough to have to go through replacement? How did the bearing look? Does the car need to be re-evaluated again (and thus may fail)? Are there discounts for the second bearing? Or is the recommendation to go with the solution (which is probably what I will do)?
Mike
Strange things I have in head, that will to hand.
2000 Ocean Blue 996 Carrera 2
1982 928 (sold)

Post Reply