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YOUR RESEARCHIMS Bearing ALMOST failed
Reported or suspected cause
original wastegate, and it was weak
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Leading evidence: 'original wastegate, and it was weak' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'original wastegate, and it was weak' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Clean anyway' (1 discussions). For that action, 0 discussions report a resolution and 0 report an unsuccessful attempt. No action has an explicit, attributable resolution report under the current rules. These are forum reports and suggestions, not a confirmed diagnosis.
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Performed · outcome unconfirmed
MY 02+ is 99.99% single, but Jake mentioned an 03 with a factory installed dual that he came across once.
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Performed · outcome unconfirmed
That's not a 100% cure, but well used cars seem to have a lower frequency.
Use he'll be installing a new oem nos intermediate shaft
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Performed · outcome unconfirmed · Original poster
As I mentioned before, the original intermediate shaft will not be used, he'll be installing a new OEM NOS intermediate shaft.
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Performed · outcome unconfirmed · Original poster
Virtually everything else is being replaced, and in some cases 997 parts are being used, such as the chain tensioners which were significantly upgraded for the 997 to include large springs that help ensure that there is tension before oil pressure builds.
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Suggestion
That's a good sign that he's going to go "all the way" with the re-furb/re-build and not just blow smoke up your butt...Do you know if he's going to do an Ultrasonic cleaning of all the engine parts like FSI would do?
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Performed · outcome unconfirmed · Original poster
Virtually everything else is being replaced, and in some cases 997 parts are being used, such as the chain tensioners which were significantly upgraded for the 997 to include large springs that help ensure that there is tension before oil pressure builds.
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Last fall I had a major water pump failure that resulted in pieces of the plastic impeller getting ground off and circulated throughout the engine, so after consulting with several people it became clear that I needed to have the entire coolant system flushed and have the cylinder heads removed for a full cleaning (otherwise the heads would have eventually developed hot spots and cracked). I originally planned to send the car off to Flat6, but they were backed up for three months and the local PCA members said we have a very highly qualified 996/997 specialist in our area (doing 996 and 997 race engine work since 99, and has never had a single one come apart), so he's doing the work.
Since it has 75k miles and has sat in storage several times, sometimes going many months in a row without being driven, I agreed to do a full teardown with all new bearings and several other bits (new chains, IMS bearing, chain tensioners, AOS, etc. etc.). The engine is currently disassembled and it's mostly great news. With the exception of the IMS bearing, all internals are in excellent condition! The IMS bearing was absolutely on its last leg, and I am actually very lucky that the water pump failed when it did, or things would be much worse by now. The builder said that it's the worst condition early-996 double-row IMS bearing he's ever seen that hadn't failed, and that it could have potentially been a few starts away from catastrophic failure, and invited me over to take a look. The videos below show the IMS shaft with the bearing still installed, first with the cover still installed, then with the cover removed with full view of the bearing. I also have a pic of the busted ball cage that fell out after we popped the seal off.
Spinning IMS Bearing from 1999 996 3.4L with 75k miles - YouTube
IMS bearing cover plate removed, 1999 996 3.4L with 75k miles - YouTube
Ball cage from the outer row of a dual row IMS bearing from a 1999 996 with 75k miles.
Damn. Talk about making lemonade out of lemons! Sorry the pump failed, but glad it let you save the motor!
So the cage was busted but the seals were still in place?
The only reason it lasted that long is because its a dual row bearing... But... If you look hard enough you'll find collateral damage that came from the wear debris suspending into the oil. This is usually seen on the cam journals in the cylinder heads, and their caps.
The big issue with a dual row bearing is it can take too long to fail, and it has twice as many wear components to generate debris than a single row. Regardless, that bearing was at Stage 3 failure. It had failed, it just hadn't came apart yet (stage 4).
Given that the seals appear to have stayed in place, would it really have allowed enough debris out to cause significant collateral damage? It seems like anything that could have escaped would have been of a size and amount that I wouldn't expect to be able to cause significant damage.
Given how little flow the seals seem to let through, it would seem to reason that the majority of the debris would have stayed in the bearing and hastened it's demise. Is there more flow than I'm giving it credit for at operating pressure?
Absolutely!!!!
I do t k ow why everyone discounts the tiniest of particles of this material that are super hard. I am not worried about chunks doing damage, they stay in the sump. I am worried about the tiny particles that are light, and easily suspend themselves in the oil. This allows the oil to deliver them to every internal part of the engine, and start taking parts out one by one.
The smallest of particles are the ones that are the most damaging, and they can easily escape from a failing bearing that still has seals in place. There's so much splash lubrication of engine oil in the region that it washes the debris right back to the sump.
This is why it's imperative to carry out all IMS Retrofit work prior to a bearing failing, and certainly before it reaches the point of this one. Once the bearing begins to fail it should be disqualified from retrofit.
With the bearing at stage 3 failure damage to the IMS shaft assembly may have already occurred. The rear most drive sprocket is lightly staged with 1/4" of engagement, so the vibration and trauma of the bearing failing can create runout on this sprocket and that can make the drive literally fall off later down the road (MOF 24), or it can have enough runout to compromise the drive chain (especially the early duplex units like this one in the video).
Worry more about the damage that can't be seen.
Thanks Jake.
In an example like this with intact seals, would you expect there been enough debris out in the oil that a magnetic plug or examining the filter (sans microscope) would have given enough sign to be concerned?
Yeah I was wondering about what impact the amount of play shown in the video could be having to the IMS itself and the parts it drives (and is driven by).
I believe from past discussions that he is saying he would not have done (and no certified installer should be doing it either) just the swap. He would have required the motor to be torn down (like it already has been) and rebuilt to address any of the collateral issues.
This bearing has failed! It just hasn't come apart yet.
The Code Of Conduct that we created for all Certified Installers is followed here, as we lead by example. There is no way that an engine with a bearing in this condition would pass the 11 step checklist that is required for an engine to be qualified for retrofit.
Doing these things and taking this seriously is how we have almost 550 IMS Retrofits under our belts with zero post- procedure failures or complications.
At the point that the bearing has failed, the process is no longer preventative, it becomes reactive. Complete disassembly and ultrasonic cleaning of every part is the only way to remove this debris.
I'd be interested to learn from the OPs mech what was left in the sump when the oil was drained and a picture of the pleats of the oil filter. Also a pic or two of the cam lobes?
This pretty much makes my decision to add a remote particulate oil filter to my engine mandatory.
This is the key sentence here for me: "Since it has 75k miles and has sat in storage several times, sometimes going many months in a row without being driven"
Drive it often like you stole it, change the oil frequently and the factory double rows will be fine. I truly believe that. Glad your engine was saved.
I've heard that advice and I agree. The problem is that we move a lot (normally long-distance, transoceanic moves), so it's just not entirely possible with all of our moves. We've had the car for over eleven years, moved the car with us three times but we moved five times. We haven't been able to take it with us everywhere we go.
Regarding Mr. Raby's concern, the builder is not reusing the intermediate shaft.
Thanks for chiming in on the thread Jake!
I don't know if he analyzed the oil or inspected the filter. I only had fifteen minutes to stop by the shop Thursday, and the IMS bearing discussion occupied all of that time.
To reinforce Mr. Raby's point, here is a picture of the seal surface of the block where the IMS bearing cover is installed/inserted. There was definitely a lot of vibration here.
From the photo, it looks like your mechanic has the case split already. That's a good sign that he's going to go "all the way" with the re-furb/re-build and not just blow smoke up your butt...Do you know if he's going to do an Ultrasonic cleaning of all the engine parts like FSI would do? Also, how are they going to address the wear in the bore for the IMSB flange? It seems that area might want to leak regardless of a new seal. Any more photo's you (your mechanic) could provide as the process progresses would be great!
Interesting thread, thanks for posting. This reminded me to order my replacement water pump, which I did.
I'm going to perform all sorts of maintenance to the car, but to be on the safe side, I'm going to stop driving it for good. Think how good I will sleep!
I'm sure the 951 will keep you happy while the 996 is parked.
I've been using the 951 as a daily driver since the 996 water pump went out, and the 951 has been a blast, especially since I added a few shims to the wastegate a week ago. I gained almost 4psi with the shims, and boost builds much faster! It was the original wastegate, and it was WEAK.
Jake, would a magnetic drain oil plug pickup the IMS particles?
Would UOA see higher metal content (if so what metal type?) ... also would cutting open the filter at each oil change reveal any symptoms or clues?
By engine number? Not that I'm aware of.
MY 99 is definitely a dual.
MY 00 and 01 are like a boxes of chocolates.
MY 02+ is 99.99% single, but Jake mentioned an 03 with a factory installed dual that he came across once.
Has there been a case of a 99 with it's motor original that had a single and it's still a safe bet on any MkII having a single.
Don't the variants have different flanges? I seem to recall reading or seeing a pic that the "cup" of the single row flange is deeper. If so they you don't need to actually have it out, but you still have to have the transmission out so it doesn't really save you much.
So two years of of "box of chocolates" then
If this can help but use with care: I made this note in my '00 996 document a few years ago from either a Rennlist or Renntech post:
- Double-row IMS: Engine #s up to 661 14164
- Single-row IMS: Engine #s from 661 14165
It seems that late '00s might be single-rows and 01's could be either without rimes or reasons.
Thats inaccurate. We see them all the time that do not follow this directive. Any 2000 or 2001 model could have either bearing. A visual inspection is required.
Some, but not all.. Some is not enough.
If a bearing has began to fail, the bearing has already failed as far as we are concerned. The engine will always see some sort of collateral damage from debris thats large enough for the eye to see, no matter how fine that may be. No, the factory oil filter will not remove all of this, especially with it's suck *** bypass design that bleeds oil by the filter at every cold start.
I can't believe I missed this IMSB thread for 4 days. So some more questions.
With the case damage shown will the flange still seal and hold the assembly secure? How much damage to the cams, crank, etc? C'mon, more info.
I stopped by the shop again today. The builder confirmed that the crank and camshafts were in excellent condition (they were fully inspected and measured) and are being reused. The cylinder heads were not damaged, but had to be completely disassembled for ultrasonic cleaning anyway, so they got a full rebuild. As I mentioned before, the original intermediate shaft will not be used, he'll be installing a new OEM NOS intermediate shaft. Virtually everything else is being replaced, and in some cases 997 parts are being used, such as the chain tensioners which were significantly upgraded for the 997 to include large springs that help ensure that there is tension before oil pressure builds.
He said the damage to the sealing surface for the IMS bearing cap is not a big problem, he can clean that up, and said he's actually worked with other blocks where this was in much worse condition and he was able to remediate it.
"He said the damage to the sealing surface for the IMS bearing cap is not a big problem, he can clean that up, and said he's actually worked with other blocks where this was in much worse condition and he was able to remediate it."
That's good to hear! Did he mention how he plans to "remediate" it? Removal of material (i.e. grinding /machining) will create a sealing problem - afaik there are no oversized IMS flanges available... Maybe add material/weld and re-machine back to original spec.?
Second guessing him is when you start telling him how to do it (which you have every right to do as well if you feel he is not doing something to your satisfaction).
He should be happy to answer any question you have about the work so that you understand what is happening and how it will effect your engine in the long term. If not, then he isn't someone you want working on your car.
Certainly don't waste his time with simple stuff, but something like this is important and you need to be satisfied with his answer.
If it was a shop I wasn't sure I could trust, I would want to know everything. In this case though, I'm working with a top tier builder, and he's happy to let me stop in any time. I went to him upon recommendation from the other German shop in town and local PCA club officers. Looking around the Internet, I've seen nothing but glowing reviews from everyone, including Charles Navarro of LN Engineering (who among many things also designed the IMS retrofit with Flat6).
I get that. All I'm saying is that asking questions doesn't mean you don't trust them or anything like that. Just that you are interested in the process and results. Of course if you aren't, there's nothing wrong with that. I'm just super interested in that kind of stuff even if it's not something I could put into practice. How things work just fascinates me
^Me too^ I didn't mean to come off like I didn't believe what they were doing, just trying to understand their process/techniques... I love the idea of fixing things instead of throwing them away and starting new - although I also understand that there is a time/place for that as well. There's just way too much of "that can't be fixed" type of attitude due to sheer laziness, incompetence or greed (or all three) for my comfort. Once again, best of luck with the motor!
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