M S4

The Ducati Monster S4 brought genuine superbike engineering to the original Monster shape in 2001. Its liquid-cooled 916 cc Desmoquattro V-twin makes substantially more power than air-cooled Monsters, while retaining the steel trellis frame, round headlight and upright riding position. Strong Brembo brakes and adjustable suspension make it fast and characterful, although it produces more heat and demands stricter maintenance. The S4 is a distinct model and should not be confused with the later S4R.

Request proof of correctly timed belt changes and desmo servicing, including valve clearances. Check cold starting, coolant temperature, fans, expansion tank and leakage around radiator and hoses. Inspect regulator connectors, battery and charging voltage. The dry clutch may rattle, but slipping or aggressively grabbing indicates wear. Examine the tank for swelling or corrosion, frame and steering stops for crash damage, and swingarm and steering-head bearings for play. Original exhaust, ECU and airbox make diagnosis and valuation easier.