spun bearing?

[68_GMC_910]

eh... I got another dumb question...

what does the term "spun bearing" refer to?

[Gee_Emm]

The term spun bearing refers to what happens when the bearing,( a thin piece of curved metal) is worn down so much in a connecting rod or crankshaft that it comes loose.

[68_GMC_910]

thank you very much, Gee emm!

[68_GMC_910]

oh yeah, and Jones Soda rules all!

[PanelDeland]

Engine bearings are actually an insert type bearing.Think of a bushing cut in half to make two half circles.One is put into the block or rod; the other goes into the cap.Each has a small tab or nub that keeps it from turning. They have a hole and usually a small groove to allow oil to feed between the bearing and crank.The pressure of the bolts clamping the cap causes the tab to keep the bearing fitted into it's half of the housing and stops it from turning.
When the bearing does turn it is called a spun bearing.It usually damages the crank and maybe the cap.There are several causes, some of which are,
1)loss of lubrication;causes the bearing to weld to crank
2)wear;bearing gets thin enough that the tab can pass it's recess and the bearing can turn
3)lack or loss of torque.
There may be some causes I haven't thought of.
Hope this makes the "spun bearing" a little more understandable.

[Gee_Emm]

Another reason could be not big enough journals being made, like in the case of my 84 s10 blazer 2.8

[CoryM]

Bearings are 2 halves that make up a circle that surrounds your crank journals. In a perfect world the bearing should never touch the crank because there is oil in between. However in the real world sometimes there isnt enough oil in between and they contact. It doesnt take long for the bearing to weld its self to the crank. Then the welded bearing goes for a ride and rams itself around into the other halve of the bearing. Then the engine makes awful noises and you gotta open up your wallet. Yes that is experience talking there. Often a spun bearing will destroy EVERYTHING. Sometimes the block is salvagable.
CoryM

[Longhorn Man]

And sometimes you can take a high nickle block with 3 spun bearings (yes...3!!) and 2 bent rods, and trade for a complete 400 small block. That's how I got the 400 that is in bloo's barn.

[Michael A. K. G]

You can spin other types of bearings, too.

There are two integrated ball-type bearings in the Saginaw 3-speed transmission. If the tranny were to be run dry, the balls would weld to the inner and outer races. The only way for the bearing to continue to turn would be for one of the races to break loose from its bore, and spin. Usually, it's the outer one because the inner one is pressed on tighter.

A spun bearing usually damages whatever it is installed into or on. That's usually something expensive, like a mainshaft, transmission case, axle housing, etc.

You can spin wheel bearings and differential bearings, too. I suppose you could spin the bearing caps on a U-joint, also, though I haven't heard of that happening.