GM-51454 is used to protect the crankshaft bearing surface from damage caused by nicking or scratching during the removal or installation of the piston and connecting rod. The two guides from GM-51454 are installed into the connecting rod after the cap is removed, guiding the connecting rod off the crankshaft throw. During installation, the guides enable the technician to ensure the connecting rod is properly aligned and protect the crankshaft from damage.