how does someone spin a bearing?

 

Lack of oil pressure is the normal cause. Excess friction causes the bearing to heat up, then stick to the journal and spin with it, instead of staying mounted in a rod or main bearing cap.

 

thanks a lot shoe box. if anyone else can figure out whatelse might spin a bearing please let me kno

 

Running the car low on oil (the engine looses oil pressure and spins the bearing as shoebox said). A failed bearing is normally caused by a damaged journal or even a defective bearing in rebuilt engines.

I've heard excessive RPM will spin a bearing but not sure why

 

wrong sized/clearanced bearings will do it too.

there's supposed to be .002" between the bearing and the journal. if there's less, it will be tight and the oil will not flow freely. if there's too much, the oil will move out of the way and the journal will actually hit the bearing, and not glide on oil. when the journal hits the bearing it moves...and then it's spun...and then you have to replace or fix the crank and use specific bearings for your journal.

 

If the motor has a ton of mile on it, the rod "big-ends" will begin to get egg shaped. The cap especially will become deformed. It's mostly normal wear and tear. So evenually the rod will not be able to hold the bearing shell.
Upon engine start up the loose bearing may stick to the crank journal and it's down hill from there.

(that's another way to spin a bearing).

Karl Ellwein

 

Cant you also spin them from debris (dirty install, other failures, etc)? the debris gets in the bearing and chews everything up then spins.

 

but the engine was never rebuilt. and 105k but ran like a dream for the seven our trip before i spun the bearing. i just hit a water puddle and it died. no oil in motor tho. don't know how i did it?

 

how come so many people spin a bearing after a cam install then?

 

well, mainly because of this:

And, YES, you can. lol. Ask Shoebox or a number of others. I thought I was breaking new ground by doing a poll of how many spun bearings after a cam install and ~22% spun one....I think Shoebox was one. Bad luck on install jobs will do it too...remember, its a garage, not a sterilized surgery room.

 

Mine was not because of dirt or debris, though. I attributed it to worn bearings and insufficient oil pressure at high RPMs.