Head-Mechanics

crank shells and big end shells and basically bearing made from a special type of metal normally white metal. white metal is an alloy which is designed to withstand the stresses from the crank but wear before the crank wears. The bearings are fed with oil under high pressure. This pressurised oil is what separates the bearing shells from the crank. This area were the oil sits is known as the bearing journal. making it a journal bearing. The crank therefore actually floats on oil.

Badly worn bearing shells                                  Normally worn Bearing shells

none of these bearings above are perfect but you can distinguish between them the differences. the left bearings are badly pitted with a substantial amount of the bearing missing. The bearings on the right show excessive wear on the edges and at the one end of the bearing

The bearing then rely on a good delivery of pressurised good quality clean oil. if any of these aren't present then the bearing shells will suffer and will need replacing. Below is a picture of a crank which didn't receive oil at the correct pressure. You can see were the bearing has scrapped away at the crankshaft bearing journal/pin.

The oil pressure in this crankshaft wasn't maintained because the oil pump wasn't delivering oil at the correct pressure. on closer inspection it turned out that the oil pump wasn't at fault, the woodruff key which held the oil pump gear onto the crankshaft was missing and therefore the pump was not spinning at the correct speeds.

We can fix it.