Archives: Italian Masterpiece

 

The 250cc Benelli G.P. racer on display at the Birdwood Mill National Motor Museum in the late 1980’s

It was in the mid-1970’s that I first stumbled across the exotic little Benelli 250cc GP bike.  I’d made my usual pilgrimage to South Australia’s motorcycling mecca, which at that time was Adelaide’s Pirie Street, where I spotted the green and silver racer.  It was prominently displayed in the doorway of one of the many motorcycle shops that had come and gone over the years and whose name now eludes me.  The price tag tied to the alloy clip-on handlebar said $3,200, which seemed a lot considering I’d paid “only” $1,800 for a new Z1 900 Kawasaki, although I had no idea at the time of how rare the Benelli was.

My second encounter was some years later during a visit to South Australia’s Birdwood Mill National Motor Museum, nestled in the Adelaide Hills.  Taking pride of place in the motorcycle display was the Benelli, but more surprising was a sign declaring it to be Australian Kel Carruthers’ 1969 250cc World Championship winning bike!

Over the years since that second chance meeting I’ve found the idea of a rare “works” racer – and a world championship winning one at that – finding its way into an Adelaide motorcycle shop extremely intriguing.

With my curiosity finally getting the better of me I decided to ring Jon Chittleborough, the curator of the motor museum, with the intention of putting together an article on the said GP racer.  Jon confirmed that the bike was still on display at the museum and that I was quite welcome to come along and photograph it.  But since becoming curator he had been unable to confirm if the Benelli was, in fact, Carruthers’ championship winning bike as its past was rather foggy.

A masterpiece.

A masterpiece.

But before we go any further a brief description of the 250 fours evolution is perhaps called for.   It was in mid-1960’s that Giovanni Benelli and Ing Savelli introduced a totally new design four cylinder 250cc GP machine that would eventually replace their ageing D.O.H.C. single.  In true fifties’ style the prototypes chassis was rather bulky and over-engineered, while on the other hand, the rim sizes were a narrow 2.590 x 18 front, with a matching 2.75 section rear.  The engine was a dry sump design with vertical cylinders, double-overhead camshafts and two valves per cylinder.  Bore and stroke measured 44 x 40.6mm for a capacity of 246.8cc, which was retained up to Carruthers’ world title-winner.  Benelli claimed 122kg (268lb) dry weight for the bike and 40bhp at 13,000rpm, which compared quite well with the contemporary Honda of the day.

Benelli continued to rely on an updated version of their D.O.H.C. single during 1961 while they refined the untried four, so it was not until 1962 that the Benelli made its racing debut in the hands of works rider Silvio Grassetti.  Many changes had been made to the machine since its first appearance, mainly the removal of the oil tank from under the seat in favour of a large-capacity bolt-on sump with a two-way pump mounted above it, and running off the camshaft drive pinion.  Ignition on the prototype had been by battery and four coils with the points driven off the end of the inlet camshaft.  This system had proved unsuitable as the four-lobe contact-breaker points tended to float at high rpm effectively reducing the engines ability to reach maximum revs.  A Lucas magneto was installed on the right front side of the crankcase and bevel-driven of the camshaft pinion, which also had the desirable effect of reducing weight. The chassis was also partly redesigned and slightly wider sections tyres fitted.

The Lucas magneto fitted to the earlier model of the 250cc GP racer.

The Lucas magneto fitted to the earlier model of the 250cc GP racer.

1964 saw the great Italian rider Tarquinio Provini join the team.  He had been runner up in the previous year’s title riding a supposedly obsolete Morini single, only losing out at the last round in Japan to Jim Redman’s Honda four after each had won four races apiece.   The former two times world champions influence at Benelli was soon apparent with the factory completely redeveloping the bike.

The frame was made smaller and lighter helping to bring the overall weight down to 112kg (264lb) dry.  New camshafts were installed which raised the rev limit and narrowed the power-band giving 48bhp 14,500rpm.  To compensate for this a seven-speed gearbox replaced the original six-speed unit.  Two pairs of 20mm Dell’Orto’s provided Carburation with a single flat-sided float bowl between each pair.  Provini was the first to reap the rewards of these changes by defeating the Honda, Suzuki and Yamaha works teams at the opening European GP held in Barcelona’s Montjuich Park, although the rest of the season only produced a fourth and two-fifth places.

More alterations were made for 1965, with modified inlet and exhaust ports for better breathing, and new camshafts offering greater lift and dwell.  Combustion chambers and piston crowns were given more squish area, while larger 24mm carburettors were fitted with specially tuned bell-mouths that gave an extra 2bhp.  Usable power now started at 8,500rpm and lasted to 14,500rpm at which point it was producing 52bhp.  However, the most significant change came in the form of a new magneto from a Mercury two-stroke outboard motor, modified for four-stroke use.  The Lucas unit had been originally designed for the lower revving 350 and 500 fours produced by Gilera and MV in the 1950’s and proved unreliable when engine speeds went over 12,000rpm.  The American made unit solved the problem and was retained to the end of the model’s development, although some experimentation was done with an early form of electronic ignition.

Beautiful sand-cast engine cases.

Beautiful sand-cast engine cases.

The chassis was also modified for 1965, being lowered and shortened even more, and equipped for the first time with disc brakes.  Benelli was one of the first in GP racing to adopt this now universal feature.  Unfortunately, the US made Airheart disc brakes were originally designed for go-kart use, and this, plus a lack of brake pad choice, resulted in the twin 7in discs being insufficient to stop an 112kg motorcycle at 143mph, which the Benelli was by then was capable of.  By the end of the season, the team had reverted to drum brakes all round, especially after suffering braking problems in the pouring rain during the Italian GP at Monza, which nonetheless did not stop Provini winning in convincing fashion by lapping every other finisher on the Italian four.

Meanwhile, the desperate struggle for supremacy in the 250cc class raged between Honda and Yamaha, accelerating development of their race bikes.  Honda’s 250cc six-cylinder was now producing 60bhp and starting to handle thanks to the talents of Mike Hailwood.  Benelli had to do something if they were not to be left behind.

Ing Savelli’s answer was to introduce a stop gap model in the winter of 65/66 with three valves per cylinder, using two inlet and one exhaust.  This helped to increase bottom-end torque but not top-end power, so inevitably a leaf was taken out of Honda’s book and four valves per cylinder were adopted.  This narrowed the power band again but increased safe maximum revs to 16,000 and boosted the engine’s output to 55bhp.  It was on this machine, now painted slate grey instead of Benelli’s more colourful green, that Provini won their third consecutive Italian national title but failed to make any impression on the Japanese bikes in the Grands Prix.  Then tragically, while practising for the 1966 TT at the Isle of Man, Provini crashed and seriously injured his back ending a great racing career.

This was a serious blow to Benelli, but they decided to continue on and enlisted Aermacchi rider Renzo Pasolini for 1967, although it was not until 1968 that he started to show his full potential on the 250 by winning the Italian title and coming second in the TT.  By 1969 both Honda and Yamaha had withdrawn from GP racing giving Benelli perhaps their best chance at the title.  Pasolini proved as much by winning all seven races of the keenly contested Italian season-openers and was the pundits choice for the world championship.  Sadly, he crashed in practice for the first GP at Hockenheim and was injured seriously enough to miss the first three GP’s, including the important Isle of Man TT.

The Bennelli has a purposeful look.

The Benelli has a purposeful look.

The Spanish Ossa factories remarkable monocoque two-stroke single, in the hands of Santiago Herrero, easily led the championship, forcing Benelli team manager Nardi Dei to enlist the services of reigning world champion Phil Read and privateer Aussie Kel Carruthers’ for the TT.  Read retired during the race but Carruthers’ swept to victory more than three minutes ahead of Frank Perris’ Suzuki.

Kel was rewarded with a place on the team for the rest of the season even after Pasolini returned to win the next GP in Holland.  By this time Herrero’s challenge had begun to wane and it was left to the two Benelli riders to slug out the remaining rounds.  Unfortunately, Pasolini fell again in Finland putting himself out for the rest of the season.  Carruthers then became team leader and his less powerful two-valve engine was replaced with the eight-speed four-valve unit, which he used to notch up two wins and two-second places in the remaining four rounds to take out the world title.

American made Airheart disk brakes were originally designed for go-karts.

American made Airheart disk brakes were originally designed for go-karts.

It was indeed the 250 fours swan-song, winning the championship at its last gasp.  The FIM in their wisdom had changed the rules at the end of 1969 for the 1970 season, limiting the 250 class to two cylinders and six gears, which also prevented Benelli from showing off its mind boggling prototype 250cc V8 racer in public.

As the amiable Jon Chittleborough and I sat down in his office at the Birdwood Mill Motor Museum, it became apparent that there was quite a bit of mystery surrounding this particular Benelli.  Unfortunately, the racer was obtained when the museum was still in private hands and there’s very little in the way of records to go by.  Jon has written to the Benelli factory in the hope of finding out a little more of the 250’s history but regrettably Benelli English is even worse than the fabled Ducati English!

It is known, however, that the GP racer was brought into this country via Melbourne, probably by John Skepper of Zeltex Imports, who it’s thought was the importer of Benelli at that time.  The Museum acquired the Benelli as a straight swap for a 1927 DS Harley Davidson after the local agents were unable to sell it.  A previous employee of the Museum believed the Benelli was obtained from Carcycle (now Peter Stevens Motorcycles), but after checking with Mike Harris and Jim Russell (who had both been with Carcycle and its subsidiary sales team for over 20 years) this proved to be untrue, although Jim vaguely recalled seeing it for sale across the street in a shop that traded under the name of “Maintenance Services”.

Jewel-like engine is extremely compact.

The jewel-like engine is extremely compact.

Before the swap with the museum could go ahead the importers had to get approval from the Benelli factory, which they did with the understanding that the 250 would not be raced.  This brings us to the next part of our mystery and probably the saddest part of the story.  The museums’ Benelli has had its engine entirely gutted. Whether this was done before the bike left Italy or after it arrived in Australia is not known for sure, although former road racer John Maher did tell the Museum he was offered a ride on the 250 GP racer by John Skepper when a Benelli 750cc six failed to show up in time for the Castrol Six-Hour production race.

It also confirms what I was told by the salesman at the motorcycle shop, who had assured me that the bike was still competitive with the production TZ Yamaha of the time.  This creates the possibility that the engine parts could still be lying around in a dusty corner of someone’s garage.

Riders cockpit.

Riders cockpit.

Perhaps the most contentious issue is whether the museums 250 was the one used to win the 1969 World Championship.  Both Jon and I agreed it was probably an earlier model, possibly 1965 as it’s fitted with the Airheart disc brakes, Lucas magneto, and “straight” megaphones of that vintage.  To add credence to this, about eleven years ago, Derek Pickard of Road and Race magazine visited the museum and opined the view that it’s the bike that took Venturi to fourth place in 65/66 Italian Championships.  Nonetheless, it’s still a very rare motorcycle, (even prompting seven times World Champion, John Surtees, to approach the museum in an attempt to acquire the 250 to add to the 500 he has on loan from the factory) as there are very few “complete” 250cc fours in existence.

However, the museum would love to hear from anyone who can shed any further light on the Benelli, especially with regards to the missing engine parts as the museum would love to fully restore the 250.  The museum can be contacted by writing to The Curator, Australian National Motor Museum, Main Street, Birdwood South Australia 5234.

Words Geoff Dawes (c) 1989. Photographs Geoff Dawes (C) 1989.Published in the November 1989 issue of Bike Australia.

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