18 captured repliesDiscussion pagination complete · Source accounts, not a confirmed diagnosis
THIS DISCUSSION / SOURCE-DERIVED OVERVIEW
Discussion summary
YOUR RESEARCHSpun Rod Bearing, OK, but why on cylinder #1?
Reported or suspected cause
pathway of oil through the internals of the engine
Reported cause
No successful repair reported for this finding.
1
Identified cause
0
Suspected cause
0
Reported fixes
Read evidence and context
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Reported cause
This is due to the pathway of oil through the internals of the engine, which the factory diagrams do not convey correctly.
Leading evidence: 'pathway of oil through the internals of the engine' (1 discussions report identifying this cause; no attributable repair resolution). Across 1 matching discussions, the most frequently mentioned possible cause is 'pathway of oil through the internals of the engine' (1 discussions; 1 report identifying it and 0 suggest it). The most frequently discussed action is 'Check carfax and look at the mileage timestamps' (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 · Original poster
I carefully cleaned oil passages hoping to find a blockage but found nothing.
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Performed · outcome unconfirmed · Original poster
I was informed the oil had been changed 3000 miles ago, I have yet to verify this.
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Performed · outcome unconfirmed
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.
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Suggestion
Check your carfax and look at the mileage timestamps.
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Rennlist: 1 discussions
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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
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.
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.
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...
#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.
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.
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.
Sorry OP, didn't mean to hijack your thread - just show my version of your pain...
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.
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...
#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.
I get that the rod is collateral damage. I do not want the rebuild and have the same issue and I am so far not clear as to why the main bearings, closest to the oil pump, had such a melt down. Have not found an obstruction that would have starved the oil feed.
Car has never been tracked. Is this attributed the poor design? Or?
Great video on cylinder scoring Jake! I particularly liked your analysis on the causes. I look forward to you doing a video on bearing failures and what the equation of causes you see here.
l cover these bearing failures in my online classes. This topic would likely create static l�d rather avoid if l shared it in public. Also, l chose not to inform my competitiors (AKA copycats) how to solve their engine failures on track. It takes years to solve this, and they should feel the same pain that l had to.
At any rate, though the #1 rod bearing is physically the closest to the oil pump, it is actually just as far away (arguably further away) from the source of pressurized oil as any other bearing. This is due to the pathway of oil through the internals of the engine, which the factory diagrams do not convey correctly.
This is a source reference. Confirm exact model applicability in the original material.
