The graduated disc for camshaft timing is a precision instrument used during engine assembly or setup to accurately determine the timing of the camshaft in relation to the crankshaft. It is a circular disk graduated in degrees (0°–360°) that is temporarily fixed to the crankshaft. Thanks to a fixed pointer mounted on the engine block, it allows the angular position of the crankshaft to be precisely read during rotation. In the Fiat 500 twin-cylinder engine, the graduated dial is used to check and adjust the opening and closing points of the valves, ensuring that they correspond to the values expected by the camshaft profile. During the phasing operation: the disc is mounted on the crankshaft (usually in place of the pulley); the Top Dead Center (PMS) of the piston is precisely identified; using a comparator or feeler gauge, you can check the exact moment when the valves start to open or finish closing; By reading the degrees on the disc it is possible to advance or delay the camshaft timing by intervening on the distribution. The use of the graduated disk is essential in prepared or overhauled engines because it allows for perfect timing, improving performance, torque and engine running smoothness. It is a very common tool in workshops specialized in engine preparation, particularly on historic engines such as that of the Fiat 500, where the precision of the timing significantly affects the final performance.
