Mercury - Quicksilver Timing Belt, 25-30HP EFI Engine Drive 57-8M0072670. Overview. On the little three-cylinder Mercury 25 and 30HP EFI motors, the timing belt is one of those parts that quietly keeps the whole engine in rhythm. Once it starts to dry out or stretch from heat and vibration, the motor won't usually quit-it just stops feeling "right." You might notice the idle wandering a bit, the throttle feeling soft, or the engine sounding like it's working harder than it should. This Quicksilv