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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 |
IMS bearing failing and shedding debris?
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IMS is in good shape.
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Did you find anything in the sump or the oil pickup?
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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. |
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 isn’t being picked up from the pickup. It’s a known problem for a lot of cars, including the M96 engine. |
Originally Posted by possumbendporsch
(Post 15559834)
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 |
Originally Posted by murphyslaw1978
(Post 15560320)
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 isn’t being picked up from the pickup. It’s a known problem for a lot of cars, including the M96 engine. |
Originally Posted by possumbendporsch
(Post 15559834)
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 Once all of that happens, the end result sounds like both of our stories... |
#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. |
Here's what my crank & bearings looked like when we opened her up...
https://cimg0.ibsrv.net/gimg/rennlis...bf7c27e2dd.jpg https://cimg1.ibsrv.net/gimg/rennlis...b13cc70d70.jpg https://cimg2.ibsrv.net/gimg/rennlis...ad020ea37a.jpg |
Originally Posted by jaetee
(Post 15572910)
Here's what my crank & bearings looked like when we opened her up...
https://cimg0.ibsrv.net/gimg/rennlis...bf7c27e2dd.jpg https://cimg1.ibsrv.net/gimg/rennlis...b13cc70d70.jpg https://cimg2.ibsrv.net/gimg/rennlis...ad020ea37a.jpg 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. |
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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Sorry OP, didn't mean to hijack your thread - just show my version of your pain...
Originally Posted by Flat6 Innovations
(Post 15572943)
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. https://cimg6.ibsrv.net/gimg/rennlis...d6dc3db6d2.jpg
Originally Posted by MattBurns
(Post 15573450)
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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#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.
https://cimg3.ibsrv.net/gimg/rennlis...b573ae3a9b.jpg #1 rod bearing. https://cimg9.ibsrv.net/gimg/rennlis...7f22a573b2.jpg Left to right, #7,6,5 4 mains. Note droplets of molten bearing. https://cimg5.ibsrv.net/gimg/rennlis...5b1741f27a.jpg Left to right, #7,6,5 4 mains. Note droplets of molten bearing. |
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