What exactly is a "SPUN" bearing?

[Helluvarush]

I see a lot of trackicks for sale around here,and seems to be a pretty common theme. " ran good,spun a bearing, $800 obo" . I'm starting to think that's what people say when they aren't sure what's wrong with it. So what EXACTLY is a spun bearing,from the sound of it,I would surmise it has somehow spun a Journal bearing in a way that has denied oil to the mating surface,letting friction and all hell run rampant.
the mains and rods are all run in babbit shells. with full oil pressure as high as 55psi at crank and idle, the metal of the babbit never touches, crank journal iron. if they touch it cause damage if allowed to progress, even for seconds at 6000rpm it the metal melts, and then siezes then the shells spin .
that is what is ment by SPUN. all automotive engine rebuild blocks cover this topic,


I ask,because I bought my second kick 3 days ago,"with a bent rod", that means the big end shell siezed,, or was so loose at 6000 rpm it ran away.
so I go through the motions,check crank cam timing, do a leak down test,adjust the valves, everything is good up to this point.

And let me say this,this is by far the cleanest engine I've seen in an 4wd vehicle from the early 90s,it looks exceptionally well maintained, no missing nuts and bolts, undercarriage has VERY little rusting just a couple spots. No dirt or oil buildup.intake manifold is spotless inside with the typical dull aluminum exterior. Point to all this is coming,I check the oil,W.T.F.?! it has 8 qts in it!
wrong dip stick or last person was a dip stick ?????? LOL
or thinks PINTS are quarts/liters. the book does show pints, for sure... and many dont get this tough in 5th grade now...

Actually 7.75,but 8 sounds better to the story. I'm thinking maybe that's caused the "knock" the PO was telling me about,so I decided to just take the motor out and go over it completely. excess oil that much 200% over causes the oil to aerate or foam up and air makes oil , more like air in a bearing gaps
and metal hits metal and boom.


Enter the "SPUN" bearing. Or lack there of.....piston #4 has no bearing,not a trace of one at all,no metal pieces,no powder no shavings I've looked everywhere and it doesn't exist.
wow they drove it to the ground, that took hard work. must have heard him coming for 10 miles away.

I'm thinking they had it rebuilt,and for whatever reason they just decided " ya know what,we've got this far in the rebuild,let's just close it up and let it ride". Has anyone ever spun a bearing in a way it just disappeared, without causing damage to the cylinder walls or anything else.I mean the connecting rod was still torqued to spec,but OBVIOUSLY very loose fitting on the crank. I'm really at a loss how that could happen other than negligence, but maybe one of you have had one of these elusive spun disappearing bearings.[/size]

there are many causes.
over filling oil in crank case.(foams up with crank counterweights bashing it and trashing it)
under filling and turning a tight turn and the pump screen sucks air and BOOM
wrong oil. or mix brands in one sump,,,
additives in the oil that (snake oil) and boom , oil is a wreck
over heated engine so bad and with cheap oil the oil failed.
water in oil, antfreeze in oil
ATF leaked there, from bad RAD cooler, (usually its the other way)
last is the oil slot in that bearing shell its small, and seen RTV glue, slivers got there and blocked all oil flow to that bearing, seen many like that.
or just running oil for 20k miles lick the SYN oil hawkers love to lie about.
running with no air clean, or that top hose cracked all ALL DO. then sucks in sand, all cars on the road , are sand eaters, all are. and you dont want that in the engine.

usually #4 lets go first, its on the weak end of pressure,
cheers good luck in the rebuild.

Thanks for the reply fixkick! When I showed up to buy it,the man started it and surprisingly it wasn't that loud,but loud enough to know something wasn't right. I finished tearing into the motor this afternoon, and NO SIGN of a bearing even being installed, like it just vaporized. Can they do that?!?!!lmao,is that what you meant by the bearing can run away? I'm starting to get the feeling this guy's mechanic was about to take him for a ride,he told me he had just had a timing belt put on then the noise started so he quit driving it. He also said his mech wanted 2600 to drop a new motor in it, on account of the bent rod.