The Dreaded IMSB
Posted: 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.
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.
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.
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.