BENELLI BLOWER

Real Classic - - Letters -

I write re­gard­ing the ar­ti­cle by Nolan Wood­bury on the lit­tle Benelli, which I en­joyed, and which re­minded me of the 250 Four they made in 1939. It was a dohc wa­ter­cooled su­per­charged four with cylin­ders across the frame, with a bore of 42mm and stroke 45mm, giv­ing 52bhp. It must have been mind-blow­ing back then in 1939 – and still would be to­day with a top speed of 145mph from a 250. Ap­par­ently the works me­chan­ics wrapped the en­gine in greased tar­pau­lin and put it down a well, out of the way of the Ger­man army as they got close to the fac­tory. It took 30 years for the mo­tor­cy­cle in­dus­try to im­prove on Benelli’s achieve­ment.

I be­lieve the en­gine still ex­ists in a mu­seum in Italy. Brian Moor­croft, mem­ber

There is in­deed a su­per­charged 250/4 in the Mor­bidelli Mu­seum in Pe­saro. De­signed by Gio­vanni Benelli and un­veiled at the Mi­lan Show in 1939, the 250 revved to 10,000rpm. The steel­sleeved light-al­loy cylin­ders leaned 15-de­grees for­ward; the head in­cor­po­rated 24mm di­am­e­ter valves and be­spoke, cen­tral 8mm Marelli spark plugs. Gears drove the twin cams and the small ra­di­a­tor was fixed to the front frame down­tube. The com­par­a­tively huge su­per­charger lived above the gear­box and its drive was taken from the trans­mis­sion. Fuel was fed by a Dell’Orto carb, through the blower which ran at half en­gine speed, via a cylin­dri­cal in­ter­cooler to four in­duc­tion stubs. This awe­some lit­tle en­gine was fit­ted into the stan­dard Benelli rac­ing chas­sis of the day, with girder forks and plunger rear sus­pen­sion. Leg­end has it that not only was the mo­tor stored in a dry well dur­ing the war years, the chas­sis lived in a haystack un­der a barn! It’s sur­pris­ing it sur­vived, as Pe­saro was heav­ily bombed in 1940/41. Then, of course, su­per­charg­ers were banned from rac­ing in the post-war years so de­vel­op­ment of the ma­chine ceased. If Frank and I ever get to Pe­saro, we’ll seek it out… Rowena

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