Nominal crankshaft speed and engine service life (Fiesta 4)

Over-revving your engine will shorten the life of your engine. If you rev your engine too high, it can cause uncontrolled vibrations in the crankshaft or valve train. If the vibrations are too high, it can cause mechanical damage to the crankshaft or valve train. In the worst case, piston scuffing occurs, the piston cracks, or the crankshaft breaks. This usually means expensive repairs or even complete engine failure. Ford recommends 5540 rpm for Endura engines (5350 rpm for Endura-DE) and 5950 rpm for both Zetec engines as a continuous speed.