EXPERT’S GUIDE TO... WHY DUCATI DOES DESMO
Clever valve system offers extra control
Si has a TEC Diploma in motorcycle Engineering, Merton College and has 30 years of experience building, modifying and repairing motorcycles from Supermonos to CBX1000 Café racers.
Ducati and desmodromic valve systems go together like chips and mayonnaise – foreign and a little bit exotic – but what is it and why has one Italian factory embraced technology that everyone else has ignored? Four-stroke engines use poppet valves to control the passage of the air-fuel mixture into and the exhaust gas out of the cylinder. The valves are invariably opened by a camshaft, either directly acting on the valve stem or via a rocker lever. Conventionally the valve is closed by a spring or springs, usually in the form of compressed coils pushing up against a collar attached to the valve. Alternatively, a second set of cams and rockers can pull the valve closed – as championed by Ducati’s legendary engineer Fabio Taglioni – although the firm aren’t the only company to have dabbled in desmodromics. The name itself comes from ‘desmo’, the Greek for knot or link and ‘dromic’ from dromous, the Greek for a road or course.
Ducati’s rocker arms offer precise valve control