What is the mystery here? Rod bearings were too tight. They heated up and end of story. So the people putting these engines together did not get that one (and a lot more of them) right.
Or, ..... (and maybe worse?) is the oil delivery design bad and that particular journal was not getting the correct lubrication? Then we are all doomed.
I do not think the bearings were too tight. I think it may have been a combination of things.
Understand that every engine built is "Cold Tested" on a device like a Spintron. If the engine was too tight at assembly the Spintron device should have detected higher current consumption of the electric motor spinning the engine.
If the motor was too loose, this may not have been picked up on the Spintron device.
I think if the engine was too loose, the oil pressure should have been an indicator, HOWEVER, the variable displacement pump may have masked a need for more oil and the pressure was not registering as low.
There was discussion of "debris" in the crank oil passages and on the connection rods. The crank was also I believe the words were "machined out of tolerance"??? The crank is supposed to have a micro polishing of the journals before installation, this is not usually performed at foundry, but at the assembly plant shortly before the crank is installed.
I believe the bearings were scored with debris and may have started to delaminate and/or there were problems maintaining the hydrodynamic oil wedge due to surface finish and excessive clearance.
Again, I believe the variable displacement oil pump may have masked a excessive clearance issue.
I have yet to see a 6.2l failure where anyone was ever alerted of an oil pressure problem. Few, if any engines had a noticeable knock or noise.
I believe every engine failed at highway speed.
At highway speed the 6.2l is under extreme engine loading at low RPM. Typically 1500-1700 RPM and when taking a very gradual rise in the road, maybe 50-100 feet over a mile or so, the engine loading will increase to between 70-100% depending on the grade and gear. Even if the transmission downshifts from 10th to 9th gear, this is only about 100 RPM increase.
I firmly believe the 0W20 oil cushion and ability to provide a thick enough layer on the crank and rod bearings was just beyond what ever damage may have occurred to the bearings or increased clearance.
Clearly there is some validity to this just because GM has proposed changing from 0W20 to 0W40 in engines that they believe had this manufacturing flaw. Some may characterize the flaw as a "defect" but I believe this is actually a combination of "Process Problems".
The Process of correctly grinding, polishing and cleaning the crank was not performed correctly.
The Process of making sure the connecting rods were clean and free of debris was not performed.
The Process of QA to verify that the engine oil clearances by way of monitoring the oil pressure was not reliable or even possibly covered up where a constant displacement oil pump may have indicated problems.
The Process of QA to pull every 100-250th engine for tear down and inspection was not performed. GM relied too much on automated assembly and testing and it is possible even the staff working in the assembly plants were not trained to identify problems or told they are to only perform X tasks and that the testing would identify any out of spec/bound conditions.
So sad all the way around. This was avoidable. Unfortunately now the end customers of 3 model years of multiple vehicles are caught in the middle of this. 600,000k or so engines in question?? What is the right answer???
All I can say is I am on the customers side and I think GM so poorly addressed this issue that they should make a public apology an get their clearly explain what they are planning to do to address this issue and how long they think it may take.
I expect this to take 18-24 months if they have to build and replace a large number of engines.
But the remedy is VERY unclear at this moment and there appear to be differences in the remedies. Maybe there was a false start, maybe Management has come to their senses?
We shall see.
