Connecting Rods, Connect The Piston To The Crankshaft.
There are many types and causes of engine failure. The most catastrophic – and visual – is a broken connecting rod punching a hole in the block or crankcase.
A connecting rod is the part that connects a piston, which is moving up and down very quickly, to the rotating crankshaft. If the rod is broken, the crank keeps turning and can push the broken rod right through the side of the cast iron or aluminum block or the crankcase, which holds the oil.
In either case, the engine will stop immediately and the hot oil escape through the hole in block or crankcase and onto the hot exhaust causing a lot of blue smoke or even a fire.