turned once again and nothing must be allowed to shift its position the fitters reposition the engine block in order to install the 20 bearing shells in its underside the shell weighs 25 kilograms and is pushed on to the bolts of a con rod later it is this area that will have to withstand the greatest forces the up and down motion of the piston causes the crank shaft to rotate 20 times a second the forces involved are extreme and all the components will have to withstand them for many years a special procedure