DUCATI’S FIRST 350
Champion idea made real in the 1960s
Back in 1960, the biggest motorcycle model that Ducati made was just 200cc, so most people would have considered anyone talking of turning that little bike into a 350 racer to be certifiably insane. But successful California racer, Frank Scurria, saw potential where others thought none existed and began a project that eventually saw him building what was effectively the prototype of the 350cc road machines that Ducati sold by their thousands in the late 1960s and early 1970s. Frank was a California road racing champion in the Sixties and even came to the UK mid-decade with his Manx Norton to perform with distinction on the British short circuits. After returning to the States he was a winning driver on the California car racing circuits before retiring from racing to join the Los Angeles Police Department – ‘to protect and serve’ as the LAPD motto says. For much of his time with the department he did that as an undercover narcotics agent. Then, after he retired from the LAPD, rather than just sit back and draw his pension, he went to the conflict in Kosovo with one of the private security agencies. Finally, Frank decided that enough excitement was enough and he came back to California where he took the lids off the packing cases that contained the parts of his 1963 Ducati 350 racer and began a superb restoration of a bike that is now one of the most significant Ducati motorcycles in existence. Frank was a typical California hot-rodder type, who loved racing anything with wheels; anywhere, any time. There are some very nice canyon roads in the San Gabriel Mountains above his hometown of Glendale, including the well-known Angeles Crest Highway that was free of heavy traffic and a great training ground for a would-be road racer. Another big help in this respect was that the ZDS Motors shop was in Glendale and was the Western States sub-distributor for Berliner Motor Corporation, the USA Ducati importer at that time. ZDS owner Bob Blair had been a speedway racer in his youth so he understood the need for speed! Frank bought his first Ducati from ZDS in late 1958 – a 200cc Super Sport. With a bore of 67mm and a stroke of 57.8mm, this was the largest engine Ducati made at that time and it was with that little bike that the story of the first 350 Ducati began. Frank started racing in February 1959, riding the 200cc Ducati in the 250cc class and he was soon looking for a way to overcome the capacity disadvantage. This turned out to be a simple problem to solve thanks to Allan d’alo, the manufacturer of ARD Magnetos. He had used his abilities as a machinist to extend the stroke of his own Ducati to 68mm. With the cylinder bore also being 68mm, this made for a ‘square’ engine with a capacity of 247cc. The only other modification needed was the making of an approximately 00.200in thick aluminium plate spacer that was positioned between the crankcase and the base of the cylinder to raise the head and cylinder to compensate for the increase in stroke. Otherwise, it was a straightforward job to make a full 250 out of a 200 using Allan’s modified crankshaft.
FRANK BEGAN A SUPERB RESTORATION OF A BIKE THAT’S NOW ONE OF THE MOST SIGNIFICANT DUCATI MOTORCYCLES IN EXISTENCE.
Frank used one of these to build his own 250cc motor and duly won the American Federation of Motorcyclists 250cc Championship in 1961. He remembers: “It was late in that season that the project to build a 350 Ducati got started, as I had noticed during practice sessions that, on my little 250, I could keep pace with many of the 350s. “For the next event, therefore, I borrowed an over-bored (to 69mm) cylinder and piston from Bob Blair’s personal desert bike and exchanged them with my piston and cylinder between races. That made my bike 254cc and eligible for the 350cc race, in which I finished a close second behind an AJS 7R, thus reinforcing my commitment to building a Ducati 350”. In late 1961, Ducati came out with an over-square 250, with a bore of 74mm and with the same 57.8mm stroke as the 175/200 bikes. For 1962, Frank would be racing a new 250 Formula 3 Ducati for Berliner and ZDS, which only had to be maintained, so he had time to think about building a full 350 but using the new over-square 250cc engine as a starting point. He recalls: “At the first opportunity I disassembled one of the new over-square engines and, after measuring everything, I knew a full-size 350 Ducati was possible. The biggest bore I could have without making the cylinder liner too thin was 76mm. With a bore of 76mm and a stroke of 76mm, I would have a ‘square’ 344cc engine. “The obvious plus for a 350 Ducati was its lighter weight compared to a 350 Manx or a 7R; both of which weighed in at about 300lb. I was sure I could build a 350 Ducati that was 50 to 60lb lighter than that. “Now fully committed to the 350 project I acquired a complete new 1961 250 Diana, took the crank to Allan d’alo and had him change the stroke to 76mm. Allan also made an extension for the cam drive shaft, which was, of course, too short in standard form. A cylinder spacer and a spacer for the base of the cam drive shaft cover, each approximately 00.360in thick, were also necessary to match the cylinder position to the longer stroke. “Meanwhile, Bob Blair had Borgo Piston in Italy made a batch of 76mm pistons. These pistons were castings rather than being forged, so they were not as strong, but we only had one piston failure and that came much later, after a lot of testing and more than a full season of racing. “I then found out about the most significant shortcoming of any Ducati of the bevel-drive period – the cylinder head ports. I took the bare head to my friend, C R Axtell. When it came to tuning engines, he was the best around. Ax designed and built his own flow-bench in the 1950s and became the absolute master of understanding airflow through a four-stroke engine. “He looked at the Ducati head from all angles and said: ‘You can make this a little better, but you’ll never make it really good – this head doesn’t have enough material around the ports to get the shape you need.’ Anyway, I did what Ax suggested I do to make the head better and this did improve the airflow.” Changing the intake port angle was the biggest modification Frank had to make to the cylinder head and this took considerable work. Before work began on the port itself, he made a new carburettor mount in the form of a thick wedge-shaped flange tapered in two planes and welded to the cylinder head. This reduced the intake port angle from 9° to 3°, which may seem counter-intuitive but, as
Frank explained, downdraft is not, in fact, the most important factor in intake airflow. What is most important is the shape of the port and the angle of the port in relation to the valve, not the horizon. Very little material came off the floor of the port near the valve – just enough to remove the irregularities. The material supporting the valve guides remained in place in the roof of the ports, and the valve guides themselves were left intact rather than being ground down to be flush with the top of the port. This gave much more support to the valves, and reduced the chance of the top of the port cracking and sucking oil through the intake port and into the combustion chamber. Because the 13⁄ 8in Amal GP2 carburettor finally used was bigger externally as well as having a bigger choke size than the smaller Dell’ortos, it cleared the frame at an angle out to the right side. This was, in fact, a benefit as the new angle gave more of a swirl of the ingoing fuel/air charge. So that the rider’s knee would not interfere with the flow of air entering the carburettor, a guard plate was specially shaped and fitted to the carb’s air trumpet. “Race cams for Ducatis were very hard to come by in those days,” recalls Frank. “So the first camshaft I used was a standard one with the lobes built up by welding on more metal and then reground to Formula 3 specs. A later and much better cam was the Ducati ‘race kit cam’ or Daytona cam. Its timing was the same as the F3 cam, but it provided more lift. “The cylinder was bored to 76mm and the crankshaft stroke increased to 76mm. The connecting rod was X-rayed, polished and shot-peened. The piston was made as light as possible and the bottom of its skirt was knife-edged. From the 250cc F3 engine we took the internally tapered, and lighter, wrist pin (the gudgeon pin to you Brits!) and the piston squish clearance was set at 0.038in. The compression ratio was 10.5 to 1.” A major modification that Frank made was to discard the standard oil pressure routing that went to the cylinder head from the oil pump in the crankcases via the cylinder casting. Instead, he modified the timing gear/oil pump outer cover so that the oil pump could feed directly through an external steel-braided pressure line to a one-off, cam-bearing housing on the left side of the head. Two extra oil drains were fitted, both on the left side of the head. They, along with one of the existing drains from the right side, drained into a baffled air/oil separator and breather combination. This air/oil separator fitted into the threaded hole in the crankcase used for the alternator/magneto cable on the standard engine. The original crankcase breather tube did duty as an auxiliary breather. Frank also discarded both the original ignition stator and its heavy flywheel and fitted constant loss battery ignition instead. He retained just the brass centre of the ignition flywheel and used it purely as a spacer for the crankshaft primary gear. “Without the flywheel, engine acceleration speed was very fast,” says Frank. “But if I was to miss a gearshift, then the engine would cut out equally quickly!” “When it came to the exhaust system, I had no idea where to start. There was never a 350 Ducati before this one so there was nobody to go to for advice! The only way would be trial and error. I tried various exhaust pipe diameters of 15⁄ 8in and 13⁄ 4in with the final one being a 15⁄ 8in pipe as it came out of the head, then opening out to 13⁄ 4in. The length of the various exhaust header pipes that I tried was about 32 to 34in and I experimented with megaphones from various other bikes. I finally settled on a megaphone designed by CR Axtell. “Finally, a five-speed transmission would have helped, but since the engine was from a 1961 Ducati, I was stuck with only four.” Some of the engine test rides for the new bike took place (illegally!) on the service road next to the Los Angeles River, next to the Interstate 5 Freeway where it goes through Glendale, just a mile or so from the ZDS shop. “The service road gate was always locked so that unauthorised cars couldn’t get in and use the road for illegal drag races,” says Frank. “However, a motorcycle with clip-on bars could just squeeze through the gap at the gate and onto the service road. I could make a couple of high-speed passes and then scoot before the police came. I would be passing cars on the adjacent freeway and going a lot faster. As you can imagine, a small motorcycle going at over 100mph caused quite a few ‘double-takes’ from drivers of the cars that I was passing on the adjacent f reeway. On one occasion, one of these was a California Highway Patrol officer giving me a w wide-eyed stare! Fortunately, the LA River w was between us and I had time to escape b back to the ZDS workshops… “Thereafter, most testing was at Willow Ssprings Raceway, thus avoiding the possibility oof me being arrested on the roads of Gglendale! In those days, Willow Springs was juust 2.5 miles of racetrack in the middle of oopen desert, without fences or barriers. “We could drive out there in the middle of the week and test all day free of charge, as there was never anyone around to stop us.” From the beginning Frank found the D Ducati 350 engine to be strong – and it got p progressively stronger. The development of t he bike was continual and, in addition to the e engine modifications, he tried three different chassis combinations.
AS YOU CAN IMAGINE A SMALL MOTORCYCLE GOING AT OVER 100MPH CAUSED ‘DOUBLE-TAKES’ FROM DRIVERS OF THE CARS I WAS PASSING