Probably the most stressed part of the engine under constant high load and subject to continuous changing forces the connecting rod plays no small part in an engines cycle. With the small end connected to the piston wrist/gudgeon pin and the big end connected to the crankshaft both the geometrical alignment and the surface quality and roundness of its bearings are critical to good performance.
Critical to the function of any rotating component particularly at high speed are its shape and form, unwanted lobing, chatter on a conrods bearings or misalignment will effect performance. The Taylor Hobson range of Talyronds can detect and help with the subsequent elimination of any unwanted defects as detailed in the Talyrond links below.