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Spun Rod Bearing, OK, but why on cylinder #1?

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Spun Rod Bearing, OK, but why on cylinder #1?

Old 01-12-2019, 12:11 AM
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possumbendporsch
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Default Spun Rod Bearing, OK, but why on cylinder #1?

I recently acquired a 2000 996 with only 56K and a nasty knock. The oil pan and filter were full of bearing shrapnel. I fully expected to find a bad rod bearing and associated main bearing issues. What surprised me is that the carnage was all located on the south end of the crank! The knock was from the #1 rod bearing, the 3 southern main bearing had all gotten quite hot. Rod bearings 2-6 are undamaged as well as mains 4-7. I carefully cleaned oil passages hoping to find a blockage but found nothing.
I'd like thoughts on why this failed. Thanks
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Old 01-12-2019, 12:24 AM
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IMS bearing failing and shedding debris?
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Old 01-12-2019, 12:43 AM
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IMS is in good shape.
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Old 01-12-2019, 12:55 AM
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Did you find anything in the sump or the oil pickup?
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Old 01-12-2019, 01:28 AM
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Oil pan was loaded with bearing shrapnel, oil filter was full of glitter. Nothing obstructing oil pickup. Remnants of bearing material all through the engine.
Mobil 1 was about 3000 miles old. Only debris I have found is from failed main/rod bearings.
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Old 01-12-2019, 10:49 AM
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Was the car tracked at all? Have you checked the ECU for overrevs? I would post pictures if you can.

I would attribute bearing failures mostly to lack of oil lubrication at high temps, such as at the track during certain high-load g-force turns where the oil isnít being picked up from the pickup. Itís a known problem for a lot of cars, including the M96 engine.
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Old 01-12-2019, 11:05 AM
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Originally Posted by possumbendporsch View Post
I recently acquired a 2000 996 with only 56K and a nasty knock. The oil pan and filter were full of bearing shrapnel. I fully expected to find a bad rod bearing and associated main bearing issues. What surprised me is that the carnage was all located on the south end of the crank! The knock was from the #1 rod bearing, the 3 southern main bearing had all gotten quite hot. Rod bearings 2-6 are undamaged as well as mains 4-7. I carefully cleaned oil passages hoping to find a blockage but found nothing.
I'd like thoughts on why this failed. Thanks
You disassembled the engine and made this diagnosis yourself? If so, please post some detailed images. That would help the forum community to offer better opinion as you seek.
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Old 01-12-2019, 04:50 PM
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Originally Posted by murphyslaw1978 View Post
Was the car tracked at all? Have you checked the ECU for overrevs? I would post pictures if you can.

I would attribute bearing failures mostly to lack of oil lubrication at high temps, such as at the track during certain high-load g-force turns where the oil isnít being picked up from the pickup. Itís a known problem for a lot of cars, including the M96 engine.
I agree, sounds like a track mode failure. Did the PO confess to the circumstances of when the failure occurred?
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Old 01-16-2019, 05:43 AM
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Originally Posted by possumbendporsch View Post
I recently acquired a 2000 996 with only 56K and a nasty knock. The oil pan and filter were full of bearing shrapnel. I fully expected to find a bad rod bearing and associated main bearing issues. What surprised me is that the carnage was all located on the south end of the crank! The knock was from the #1 rod bearing, the 3 southern main bearing had all gotten quite hot. Rod bearings 2-6 are undamaged as well as mains 4-7. I carefully cleaned oil passages hoping to find a blockage but found nothing.
I'd like thoughts on why this failed. Thanks
Such a low miles car might have spent some time as a garage queen before you got it... Check your carfax and look at the mileage timestamps. You will see if there is a timeframe where it wasn't driven far over long periods of time. My car had #1 rod failure as well. Previous owner had clutch/RMS and IMS changed in 2011 and then the car sat six years before and moved about 300 miles in that time. After I drove it 2500 miles my journals looked much like you described. And the polished areas of my crank showed pitting visible to the naked eye, which was the result of gravity given enough time to pull the oil off of the crank and drip into the sump. After that happens, and given enough time... , condensation collects in the the gaps left by the dripped-off oil and then forms little rust pits (again, given enough time). You end up with a layer of microscopic sandpaper on the crank gradually chewing away at your bearings until there's enough room for one to tap a valve....

Once all of that happens, the end result sounds like both of our stories...
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Old 01-17-2019, 01:30 AM
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#1 and #6 are fed with oil from the outer extremities of the crank carrier. This means issues with oil delivery, or a loss of viscosity due to thermal breakdown show up here first. Also, for whatever reason the #7 main bearing (that feeds the #1 rod bearing with oil) seems to always be a little tighter on the clearance side when blueprinting these engines. A tight clearance leads to shear, which leads to wear, then that wear debris is fed with centrifugal force into the #1 rod bearing along with the oil delivery. When you induce wear from the main into the rod bearing, it has to fail.

Are your mains worn? Remember, 100% of the oil that is fed to the rod bearings has to pass through a main bearing to be delivered.
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Old 01-17-2019, 12:49 PM
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Here's what my crank & bearings looked like when we opened her up...




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Old 01-17-2019, 12:59 PM
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Originally Posted by jaetee View Post
Here's what my crank & bearings looked like when we opened her up...



Do you have pics of the wear surface of the main bearings?
That main journal looks more worn than the rod journal, which is what we normally see... In those cases the rod bearing failure is collateral damage from the main bearing wear. Main bearing wear creates debris that is directly delivered via the lubricating oil into the rod bearing... That makes for rod bearing wear, and failure.. Then people have the same problem when it goes back together, because the issue that made the main bearing wear is not addressed... Thats because they didnít truly understand the failure process, which is usually because they donít fully underatand how the engine operates.

Those are general statements, though.
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Old 01-17-2019, 04:21 PM
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That main journal looks trashed. Almost looks like material went through the main. I would be curious about the filter and bypass condition, but it definitely looks like something foreign went through the main before getting to the rod.
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Old 01-17-2019, 08:20 PM
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Sorry OP, didn't mean to hijack your thread - just show my version of your pain...

Originally Posted by Flat6 Innovations View Post

Do you have pics of the wear surface of the main bearings?
That main journal looks more worn than the rod journal, which is what we normally see... In those cases the rod bearing failure is collateral damage from the main bearing wear. Main bearing wear creates debris that is directly delivered via the lubricating oil into the rod bearing... That makes for rod bearing wear, and failure.. Then people have the same problem when it goes back together, because the issue that made the main bearing wear is not addressed... Thats because they didn’t truly understand the failure process, which is usually because they don’t fully underatand how the engine operates.

Those are general statements, though.
Thanks, Jake... Here is the best shot I have...I love how the bearings got beaten into oval shape... I ended up sourcing a crank and basket from a wrecked Boxster S (same part #s) and all of the guts were replaced during the rebuild. Special attention was given to make sure all oil passages were clear.



Originally Posted by MattBurns View Post
That main journal looks trashed. Almost looks like material went through the main. I would be curious about the filter and bypass condition, but it definitely looks like something foreign went through the main before getting to the rod.
I had LN spin-on filter adapter and magnetic drainplug on the car. None of the material we found in the pan was ferrous or plastic...
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Old 01-18-2019, 02:05 AM
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#1 rod was the lone casualty, bearings 2-6, a bit scratched from metal flowing in the oil look good. Main bearing 1,2,3 also looked pretty good. Main 4-7 are progressively oil starved, note molten material in bearing edges. I was informed the oil had been changed 3000 miles ago, I have yet to verify this.

#1 rod bearing.

Left to right, #7,6,5 4 mains. Note droplets of molten bearing.

Left to right, #7,6,5 4 mains. Note droplets of molten bearing.
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