jeb@kitc.UUCP (Jim Beckman) (09/19/85)
A technical question: can someone explain to me exactly what happens inside an engine that suffers the indignity of a "spun bearing"? What are the external symptoms - do you hear a rod knock, or what? Jim Beckman AT&T-IS, South Plainfield, NJ kitc!jeb
tmorris@convex.UUCP (09/21/85)
In most modern engines , bearing inserts are used . These alloy surfaces , often called shells, are made in two half-circles . When they are assembled in a rod or main bearing , they are the nearest metal surface to the crankshaft , forming the circular bearing surrounding the smooth wearing surfaces. In theory ,and if all goes well ,they never touch the crankshaft .They ride upon a steady film of oil being pumped through hollow passages in the crankshaft by the oil pump. And therein ,literally , lies the rub . If the flow of oil should be insufficient , even for a short time , the bearing surface touches the crankshaft . At this point , wear begins in earnest . When the friction caused by this wear creates enough torque to overcome the small keys that hold the shell in place , it rotates with the crankshaft . This can cause immense damage to the surface upon which the shell was mounted . If it is a rod bearing , it may generate enough torque to snap off the rod and beat it about the crankcase. You will definitely be aware there is something wrong at that point. Sometimes a tapping noise will preceed this catastrophe. If you suspect it , it will be worth your while to have it checked out with a stethoscope. Its the difference between a rebuildable engine and a high-tech boat anchor. If it is a main bearing , when the shell spins it will obstruct the hole in the block from which life-giving oil is pumped into the bearing and crankshaft. I have seen several blocks ruined like this , as the mounting surface for the bearing shell is destroyed beyond repair . Broken crank- shafts can also result . Sometimes a deep knocking sound will preceed failure , other times it all just comes undone.