Monday, January 02, 2012


The supercharged, water-cooled, four-cylinder Benelli 250cc racer of 1940
As the technological high points of 1920s motorcycle racing began to look, and perform, like the antiques they'd become by the 1930s, the Benelli brothers took stock of the obvious trends of Grand Prix racing; chiefly, more power from multi-cylinder, supercharged engines.  Moto Guzzi, Gilera, BMW, DKW, NSU, and even AJS and Velocette in England were racing or developing such engines by 1938.  As champions in the 250cc racing class, Benelli set about designing a new 250cc racer, with four cylinders, twin overhead camshafts, a supercharger, and watercooling.  Trends in chassis development were also attended, and as sketched, the new machine would retain the hydraulic-damped girder forks and rear swingarm suspension of their singles, plus large-diameter alloy brakes to manage the inevitable blistering speeds to come from such an engine, given Benelli's expertise with tuning small engines, especially in cam design, intake porting, and carburation.
The 1940 Benelli 250-4 as it exists today
The gem of an engine designed by Giovanni Benelli produced in 1939 had a short stroke (42mm stroke x 45mm bore), with 12:1 compression pistons, and spun to 10,000rpm, at which point it cranked out 52.5hp, enough for 146mph on test runs - the fastest 250cc racer by a long shot, fully 16mph faster than their nearest rival, the brilliant supercharged 250cc flat-single from Moto Guzzi.  With such devastating performance (exceeding by 20mph the factory 500s of Norton and Velocette!), Benelli were confident of another European Championship, but the little 'four' wasn't ready for the 1939 racing season.  By the time the 'engine bugs' were sorted, it was 1940, and the competition was no longer playing nice.
The new 250cc double-overhead-camshaft four-cylinder Benelli racing engine, introduced in 1960
Lacking martial confidence in their native Italy, Benelli race chief Vincenzo Clementi stashed the entire racing fleet in rural areas away from Pesaro; purportedly their precious new 250cc 'four' had its engine hidden at the bottom of a dry well, while the chassis slept under a haystack, inside a barn. Their decision proved wise, as during 1940 and '41, Pesaro was bombed heavily; the Benelli factory had been converted to aero engine production (Daimler-Benz and Alfa Romeo types), and when the Allies advanced northward in Italy, all the precision machine tools were moved by the German army to more secure territory inside Austria and Germany.
The new Benelli '4' racer at the press launch in 1960
While the company returned to single-cylinder racers postwar (netting them a World Championship in 1950), by 1960 Benelli's line of small-capacity motorcycles was selling very well, and funds were allocated for the design of a new four-cylinder racer. Race chief Ing. Savelli and Giovanni Benelli designed an entirely new engine which bore resemblance to the 1938 design, but in truth, by 1960 a DOHC four with gear-driven cams had become the accepted pattern for a racing engine, having been developed by Gilera (from the original CNA/Rondine 'fours' dating back to 1926!), copied by MV Agusta, and then again by Honda, who won the 250cc World Championship title in 1961.  The new 'four' used a short stroke (40.6mm stroke x 44mm bore), a 6-speed gearbox, weighed 264lbs, and gave 40hp at 13,000rpm (oh, how supercharging was missed!  This was 12.6hp less than the blown 1939 design).  The completed machine was revealed with great publicity in June of 1960, but wasn't ready to race until 1962, and Silvio Grassetti had only one 'win' that year, at Cesenatico, but it sounded a bell at Honda, as both Jim Redman and Tom Phillis were bested on their Factory Honda 4s.  MV had withdrawn from 250cc racing the year before, to concentrate on retaining their 350cc and 500cc dominance.
Tarquinio Provini on the 250cc Benelli 4 in 1965; note the 7" dual disc brakes.  These are American Airheart brakes from Go-Kart racers, and were possibly a first in GP racing, but proved inadequate on at 143mph, especially in the wet.  While the concept was sound, the brake pads hadn't yet evolved for serious high-speed use.  Benelli used them only in '65, retreating to reliable racing drums...
Tarquinio Provini, a veteran racing star with two World Championships, joined Benelli in 1963 to develop and race the new 'four'. He shortly increased power to 52hp at 16,000rpm, with a 7-speed gearbox, and 141mph top speed. A new frame lowered the center of gravity and pared weight down to 247lbs.  Years of ignition troubles with the high-revving engine were finally cured by fitting an American racing magneto...from a Mercury two-stroke boat engine. Provini won every race in the Italian championship in '64.  Benelli shocked the world by out-running the Japanese opposition at the super-fast Monza GP in 1965.
Provini hard at it in 1966
By '66, the Four had 8 gears, and a larger version with 322cc was introduced to compete in the 350cc GP events, going head to head with the 'big boys', MV Agusta, Honda, and Yamaha.    Provini had a bad crash at the Isle of Man TT that year, and injured his spine enough to retire from racing.  Benelli had never fielded a 'team' of professional riders who came and went with lucrative contacts; the family business had close bonds with the one or two racers they supported, and Provini's injury took the steam out of Benelli's race dep't for over a year.
The immortal 'Paso'; Renzo Pasolini
Benelli re-entered the racing fray with rider Renzo Pasolini, who won second place in both the 350cc and 250cc classes at the 1968 Isle of Man TTs, and dominated the Italian Championship in both classes the rest of '68, giving Giacomo Agostini and his MV and excellent view of the Benelli's tailpipes all year long.  In 1969, Kel Carruthers joined Pasolini, and the pair made an unbeatable team, each winning three GP victories that year, giving Benelli their second World Championship title.
Pasolini leaping Ballagh Bridge at the 1968 Isle of Man TT
Kel Carruthers joined Yamaha in 1970, but Pasolini took third place in the World Championship that year.  The Benelli family sold the factory and name to Alejandro de Tomaso, more famous for his automotive exploits than two-wheeled savvy, and support for developing the racers waned.  Still, Jarno Saarinen was hired in '72, and won his début races at Pesaro in both 350cc and 500cc classes.
Renzo Pasolini with Kel Carruthers
Both Saarinen and Pasolini left Benelli for '73 (for Yamaha and H-D, respectively), and Walter Villa became their #1 rider.  With horrific irony, Villa's 350cc Benelli was blamed for leaving a trail of oil during his race at Monza, which was then not cleaned up for the 250cc race, in which a multi-machine crash killed both Saarinen and Pasolini.  The details of the accident have been debated ever since, although it seems a catastrophic seizure of Saarinen's Yamaha (not an uncommon occurrence) may have led to the chain-reaction melée.
Kel Carruthers at the 1970 Isle of Man TT
Benellis interest in racing plummeted when new FIM rules limited 250cc racers to two cylinders and six speeds, which guaranteed an unstoppable rise of two-stroke racers, as their double-time combustion could only be opposed by outrageously sophisticated four-stroke engines, such as the Honda 6-cylinder, and the Benelli 250cc V-8 which was under development...which would certainly have put Benelli on par with Moto Guzzi as masterful creators of racing exotica.  The FIM, in their wisdom, preferred the crackle of two-strokes to a technical war of miniaturized-miracle racers, a decision which eventually killed Grand Prix motorcycle racing, and led to the birth of MotoGP.
Jarno Saarinen...with wife Soeli giving pit signals

Bonhams is selling a replica 350cc four-valve Benelli four-cylinder, of the type Kel Carruthers took to the World Championship in 1969, at their Jan 12 sale in Las Vegas.


Somer said...

Great piece of history on the Benelli multis.

Anonymous said...

Hi Paul,
I guess I never told you I had one of Tarquinio Provini’s Benellis [see link]. Here’s a picture to fill in that loop.
Happy New Year!

Anonymous said...

Oh mio, che cosa bella Benellis...
Michael C.

Anonymous said...

Didn't realise that the '39 250 - 4 still existed, excellent. Not so keen on the new, smaller, pop up images in the blog.
- Carl W.

The Vintagent said...

‎@ Carl; I was surprised as well! No choice in the matter it seems - I preferred the full-screen version too. I post all pix at ~250kb, which is big enough to see any detail you like.

Anonymous said...

Great story!

-Dart B.

occhiolungo said...

Paul, does Blogspot limit you to 250kb? on Wordpress they routinely go to 2Mb or more without issues.

Don O'Reilly said...

Excellent read Paul, thanks for posting.

Don O'Reilly said...

I almost forgot... If I had a bucket of money, I'd take that replica 350cc four-valve Benelli four-cylinder, fit some lights, and ride the piss out of it. does it have a clear title? I can always sell the house and garden, hehe

Anonymous said...

One correction: Saarinen rode Yamaha during 72 in TT series (and won championship in 250 class and was second in 350 class). He used Benelli only in one or two races before the season.
Also during fatal accident in Monza 73 it was Pasolini's Harley Davidson which seized, not Saarinen's Yamaha.

Anonymous said...

In this site there is a good replica of Benelli 350 gp 1969: