chsu74

What is that piece? I don't recall seeing that part when my 996 engine got torn down for its clutch, IMSB, RMS, chain tensioner paddle and lifter replacement.

Ahsai

Updates: I removed the IMSB last night and it's an LN classic single row retrofit IMSB. The whole bearing has been disintegrated. The outer race is half gone, the inner race is "fused" onto the stud and the flange. The ceramic ***** just fell out when I removed the bearing. I collected 6 ***** (missing 2. Must have fallen into the sump). They are so hard that despite all the destruction, there's only some pitting on two of them while the rest appear pristine. It's clear this is where most of the debris were shredded from. Basically, the crankshaft turns the IMS, which turns the ceramic ***** to grind down everything in their paths. It's likely the other piece I found came from here too as the diameters match.

It's quite amazing the engine still ran with the IMSB ***** all loose.

The bearing has mismatched codes. The flange says G2 and the stud says H2. The center 12-pt nut was very difficult to remove (recall spec is 7.5 ftlb). It's possible the installer had grossly over-tightened the center nut which shortened the life of the bearing. However, it's also possible that during the course of the bearing destruction, the IMS basically tightened the center nut naturally (will the ***** turning the center stud) due to its direction of rotation. It's also possible some initial debris got into an otherwise healthy bearing and set off the spiral of death. At this point, it's hard to say whether the IMSB is the source of failure or it's just a collateral damage.

Like Jake said, the metals shredded are flung around by the timing chains on bank 1/IMS, which explains the heavy damage on the bank 1 scavenge pump as it's exposed to tons of debris.

Note I had cleaned up the area before I removed the IMSB flange. Next steps are to strip the accessories/sensors from the engine and remove the heads.

Ahsai

BTW, the failed bearing in this thread also has G2 on the flange and H2 on the stud. Are the stud and flange suppose to have the same number? QC issues with this batch?

https://rennlist.com/forums/996-foru...30k-miles.html

Hopefully Jake can shed some light on this issue.

Ahsai

Most likely from the IMS and IMSB.

Paul Waterloo

Ahsai-

Thanks for the continued education. I am trying to figure out what I am looking at in this picture:



Is this the flange/IMS bearing inside race basically fused to it? So basically this flange with the bearing inside race and everything else on the bearing removed because it fell off due to bearing destruction? The following photo is courtesy of LNengineering website:



I think that's what I'm looking at, but having never done one of these, I'm still figuring it out. Does the IMS shaft fit on the ID of the bearing or the OD? This confuses me because it appears the flange "shaft" fits into the ID of the bearing, so I don't know if the ID is the stationary component or the OD. I'm sure it's simple, but it still hasn't clicked in my brain.

It appears the diameter of the flange is smaller than the ID of the bearing.

Ahsai

You have it right. The inner race is stationary, bolted down by the center stud to the flange, then to the engine case. The IMS fits onto the outer race of the bearing. The flange "shaft" fits into the ID of the bearing. Check out the nice CAD diagrams here

http://www.cheetahonline.com/technic...rofit-upgrade/

Paul Waterloo

Thanks! I almost feel smart right now!

Actually after reading this post and the other post of the failed bearing, I'm really thinking about just leaving my 99 dual row bearing with 36K miles alone for now and continue to send out the oil for analysis and keep looking at the filter/magnetic drain plug.

Continue posting! Love the progress!

cringely

Any thoughts on why it failed? Materials failure, mismatched components, improper installation, ??

Cuda911

I've lost track in other IMSB threads. Is the the first documented failure of an LN bearing? I've heard allegations before, but never seen one documented.

Ahsai

I hope Jake would chime in. Your bearing had 25k miles on it so it's hard to imagine a botched installation will last that long. The G2/H2 mismatch may give us some clues but I have no idea how they should be numbered. I will keep tearing down the engine and document what I find along the way.

See post #183. That's the first thread I saw with photos. That bearing had 30k miles on it.

Ahsai

Ok, looks like the date stamps on the shoulder bolt and the flange should match.

"All boxes will have matching date stamps on the outside which will match the date stamp marked on both the flange and center should[er] bolt."

http://imsretrofit.com/is-it-genuine/

Flat6 Innovations

Pay no attention to those stampings, they have nothing to do with graded components, or batches. Thats not mismatching at all.

Its hard to say what happened here, because we don't know which series of events came first. Debris generated from failing cylinders can easily suspend in oil and take out the IMSB, or vice versa.

Tons of variables here, and it takes exhaustive amounts of digging to determine which occurred first, and what was collateral damage.

I do see some things that are adding up, especially the singe piece of debris thats curved.

I'll help you. Email me.

Ahsai

Thanks Jake for the info and offer to help. I appreciate it. I totally agree with you about the unknown sequence of events at this point.

I'll email you once I strip it down to the long block.

Flat6 Innovations

Sounds like a plan. You are a class act, most people would be playing the victim, pointing fingers and making all sorts of drama.

You'll be rewarded!

ZX9RCAM

I was thinking the exact same thing....