ed back to Motobi in 1966. There he focused his attention on the new 250cc Sprite model introduced that year, with the specific purpose of making it a winner in the recently-introduced quarter-litre MSDS class for customers of the Pesaro factory. But by the end of the decade, competition was so intense from rival factories like Ducati, Parilla, Aermacchi and Morini that he had been forced to develop a limited edition homologation special known as the 'Sei Tiranti' (six-stud). Produced in very limited quantities this had six cylinder head studs instead of the street Sprite's four, a factor which caused problems with cylinder head sealing when compression and engine speeds were raised in pursuit of power. Considering that by the end of the decade Zanzani had doubled the 16bhp output of the street 250 to 33bhp in MSDS form, this was hardly surprising. So an extra pair of studs was grafted in to bolt the cylinder head to what on this tricked-out special were sand-cast crankcases for extra stiffness, rather than the diecast ones of the street bike. Make no mistake, this was for a silhouette c!ass, where every little trick was employed to gain an added edge. Bit like Supersport racing today, really....Imagine if Colin Seeley himself were to restart construction today of his 7R/G50-powered racebikes. Same deal.....In parallel with this, Zanzani developed a specialist expertise in the disc brake technology then new to motorcycles. He'd been the first in the world to adopt them on a GP racer back in 1965 on the four-cylinder Benelli, using US made Airheart discs rather than the cable operated Campagnolo brakes produced in ltaly for lightweight machines. Zanzani developed his own process for plasma spraying aluminium disc rotors with iron to produce a far lighter disc brake package than the steel or cast iron discs then commercially available. These discs offered notable benefits in terms of reducing unsprung weight and gyroscopic effect. His brakes became ubiquitous components on GP racers in the smaller classes, winning no less than 25 world championshp in the 50/80/125/250cc classes from 1978 onwards, up to and including Alessandro Gramigni 's 125 Aprilia World crown in 1992. Today with his two sons at the age of 77, Primo Zanzani concentrates on running the trio of high-tech machine shops his family owns in Pesaro, producing intricate components for the local woodworking machinery industry - and Motobi 250 Sei Tiranti replicas!>
'CLASSIC RACER' magazine sept-oct 199 - words by Alan Cathcart