View Full Version : Spun a bearing?

09-26-2006, 05:12 PM
Okay, I've been around cars a while and can turn a wrench, but have never really understood the term, "spun a bearing". I know that the insert bearings have a locking tab that holds them in the connecting rod and/or block/cap(in the case of a main bearing). So when a bearing is "spun" does that mean the locking tab gives way and the bearing "spins" in the rod/cap? or does it mean that the bearing surface comes in contact with the crankshaft journal (perhaps due to contamination or improper lubrication)and does damage to the journal by "spinning" on it?

Dan Peterson
Montpelier, VT
1960 Lark V-8 Convertible
1960 Lark V-8 Convertible (parts car)
1962 Lark V-8 Regal Convertible

09-26-2006, 06:07 PM
That's exactly what it means, Dan. I took apart a Rammer 6 a few years ago. It had developed a ferocious knock and it turned out that one of the rod journals had welded to what was left of the bearing halves (after it had hammered on them enough) until the rod started to rotate around the welded and ruined shells that were stuck to the crank journal.[xx(] It's UGLY!

BTW - usually ruins the rod or eventually causes it to fail if not stopped in time.[8]

Miscreant adrift in
the BerStuda Triangle!!

1957 Transtar 1/2ton
1960 Larkvertible V8
1958 Provincial wagon
1953 Commander coupe

09-26-2006, 08:48 PM
Technically, a spun bearing has come loose from the cap but, what caused it? The requisite repair is the same so, the term "spun a bearing" means either and/or both. Hope your question was rhetorical.

Brad Johnson
Pine Grove Mills, Pa.
33 Rockne 10
51 Commander Starlight
53 Commander Starlight
previously: 63 Cruiser, 62 Regal VI, 60 VI convertible, 50 LandCruiser

Dan Timberlake
03-18-2008, 10:09 PM
The locking tabs just position the inserts in the right place front to back. The inserts are held tight in the con rod by "crush" or being a press fit since the bearing OD is larger than the rod big end ID. The ends of each insert sticks up a little above the parting face so the insert ends meet before the rod and cap faces touch. http://craig.backfire.ca/imgroot/autos/chevrolet-caprice-1982/engine-rebuild/p6200024.jpg
The interference is important to hold the bearing and provide good heat transfer to the rod. Bearings "spin" as a result of seizure, usually starting with insufficient oil flow.