firemanpat2910 said:
I guess unless you've rebuilt over 100 engines it's hard to understand. In the engines I mainly worked on #2 was the case. The reason why it was number 2 because of the oil flow...straight from the oil pump...to the filter. The filter bracket was on the side of the engine at #2 (these diesels the #1 was closest to the flywheel). So even though the oil entered the galley, the closest spot was #2. As the engine runs out of oil it will begin to pick up some and and oil....hehe like my straw....it'll keep pushing some oil that's left in the far ends of the galley. The oil that actually protects the bearings is microscopic. But just enough to work, also the clearances on the bearings is in the thousands. In the "worn out" engines I rebuilt, the wear was generally equally spread out. In a general failure, I guess it's just the luck of the draw as to which one fails first. But in certain failures things can point to the problem. If I overheated my 3 cylinder diesel in most cases the piston to go first would be #2. Because it's the only one that's surrounded by heat. It may not be 100% but in trials that was the one.
In your examples I'll give you my thoughts...the loose bearing would go first IMO. Why? Because We have to start with a control...and in this case we have to say that when new the engine was all within spec. If someone installed the bearing improperly or the wrong bearing (it happens), then human error is the cause. The loose bearing will have less oil pressure, possibly effecting the oil pressure as a whole if bad enough. The pounding IMO could eventually cause a failure. I happen to be cheating on this one. My BIL just rebuilt the bottom end on his JD350 dozer. He said all he had was a standard bearing and the crank had been cut .010. So the bearing was .010 to small. The dozer ran for about 300 feet and placed a nice size hole in the block.
In the case of a piston. Actually the only friction in the cylinder wall is the rings. More wear the less friction. There is contact on top if there is a lot of carbon buildup. If the skirt of the piston ever touches the wall it's over in seconds. Remember the microscopic film of oil also protects the skirt. Also in the diesels I've rebuilt (not the gassers...interesting), the skirt is knurled (think knurled, hair thickness lines cut in it..don't know what they call it). My guess is this reduces surface area and traps oil. So what causes piston failure, rings break, ring lands give way (I hate ether), overheating causes oil breakdown. I have seen pistons gaulded and the lower end ok. Usually overheating. In most of my cases it was because the fuel pump was set for intermitting load but ended up running at a continous load. Melted the skirt.
In old engines that fail it's a crapshoot. Like I've seen in older engined the oil pump drive gear strip out. So in this case the oil flow suddenly stops. Maybe gravity feeds some parts longer than others. So maybe it's number 2 that goes first. But in the end the mechanic discoverys the problem to be the oil pump, so whether number 2 or number 6, the problem is the oil pump gear.
I'm still very interested as to what happened in this case. Another chapter to add to the book on possible problems. If the engine won't turn in either direction then something is siezed or broke and locked into place.
Pictures are always cool to.
), If I'm sucking a coke through a straw and run out of coke, I may still have coke at my mouth but the bottom of the straw is empty. And if I'm blowing air into the straw, I can move the coke at the oppisite end of the straw. So in both cases the area closest to the supply is dry first. No way I invented this stuff...the engineers I guess did. 
