Motorcycle designer Alfredo Bianchi arrived at Aermacchi’s factory on Lago di Varese in early 1956. His first task was to create a new motorcycle for Italy’s immensely important 175cc class. Bianchi could point to a successful career with Moto Parilla, and despite an unfortunate start, in due course made a big contribution to Aermacchi. Bianchi’s first effort, styled by car-guy Mario Revelli, was the sensation of the 1956 Milan show: the 175cc Chimera (Dream). With its space-age bodywork and futuristic styling, it looked more like something out of Marvel comics.
But despite positive reviews of its performance, handling, and ergonomics, buyers stayed away in droves. However, the Chimera was considered significant enough to be displayed in the Guggenheim’s Art of the Motorcycle exhibition in Las Vegas from 2001 to 2003.
That sales of the Chimera were slow is an understatement, and Bianchi was quickly asked to try again. This time, he opted for a more conventional look, with minimal bodywork, an exposed engine and a sportier stance, including clip-on handlebars, a bump-stop seat and dual rear shocks, as the Chimera used a single shock. Two versions were available in 1958, both of 175cc: the standard Ala Bianca (white wing) and tuned Ala Rossa (red wing). Italians, it seems, prefer sporty motorcycles to styling exercises!
Ala Bianca and Ala Rossa
Both the “normale” Ala Bianca and the sportier Ala Rossa retained the Chimera’s 175cc OHV four-stroke, four-speed unit construction powerplant with its trademark near-horizontal cylinder and vertically split cases. The light alloy cylinder head capped a cast-iron barrel of 60mm bore. The built-up crankshaft ran on a roller bearing big end and had a stroke of 61mm for 172.4cc. A gear pump circulated oil from the wet sump, and primary drive to the wet multiplate clutch was by helical gears. A four-speed gearbox drove the rear wheel by chain. A crankshaft-mounted generator fed the six-volt lighting circuit and provided sparks.
The Ala Bianca used an 18mm Dell’Orto UB-series carburetor for 9.4hp @ 6,500rpm, while the Ala Rossa used higher 9:1 compression and a 22mm Dell’Orto for 13hp @ 6,700rpm. The rest of the running gear was borrowed from the Chimera, including its 17 inch wheels running on 2.50 front and 2.75 rear tires, and full width alloy drum brakes. This gave the Ala Rossa a respectable top speed of around 130kph (76mph), a competitive performance in Italy’s important 175cc class.
Ala Verde, Ala Azzurra and Ala d’Oro
Within a year, the Ala Rossa was joined by a 250cc version, identical in most respects to the 175, except for bore and stroke of 66mm x 72mm for 246cc and a wider 3.00 rear tire. With 8.5:1 compression and a 24mm Dell’Orto, the Ala Verde produced 18hp @ 6,700rpm, good for a top speed of 82mph. A touring version of the 250, the Ala Azzurra, with a smaller carburetor and lower compression was also available.
The factory also produced what were essentially race-ready customer editions of the 175 and 250cc racers with the name Ala d’Oro, or Gold Wing. At first, the 175 produced 15.5hp, but increased to 20hp in 1960, giving it a top speed of 100mph. This put it in the same class as the Moto Morini Settebello, Ducati’s 175 Sport and MV’s Disco Volante. The 250 made its international race debut in the 1960 German Grand Prix, ridden by Alberto Pagani, then finished ninth and fifth in the two successive GP rounds at Assen and Spa.
The 250 version used 10.2:1 compression and a remote float 30mm Dell’Orto SS1 to produce 25hp @ 9,000rpm. Straight cut gears replaced the helical primary drive of the street bikes, and ignition was total loss battery and coil. Brakes were uprated to Oldani double leading shoe front and single leading shoe rear with magnesium hubs. Weighing just 225lb, the 250 Ala d’Oro claimed a top speed of 110mph.
Enter Harley-Davidson — and the 350.
Meanwhile, across the Atlantic, America’s senior motorcycle maker was facing a slump in sales. Since the mid-1950s, sales of its big twins had been in decline, and while their K models and Sportsters competed well with British imports, the company had no answer to the increasing flow of smaller bikes starting to arrive from Japan. Considering the option of developing small bikes of its own, H-D decided on a quicker and easier solution: buy an existing small bike maker with a suitable model range.
Aermacchi fit the bill perfectly. Its OHV engines used technology that would be relatively familiar to dealers, and there was no existing U.S. importer, leaving a clear field. Macchi needed the investment, and its owners were amenable to Harley-Davidson’s approach. In 1960, Harley-Davidson bought 50% of Aermacchi’s motorcycle division and started importing what were effectively the touring 250cc Ala Azzurra, rebadged as the Harley-Davidson Sprint C “Wisconsin,” and the Ala Verde, as the Sprint H. (In Harley-speak, H indicated the performance model.) For 1967, the new short-stroke Aermacchi engine arrived in the 250SS, replacing the Sprint C and introducing the more stylish one-piece rocker cover.
Back in Europe, the Ala d’Oro turned out to be very competitive in production racing, in 175cc classes on the Continent, and in the 250cc class in Britain and the U.S. Their overhead valve engine technology may have seemed pedestrian for a race bike, but provided the benefit of simplicity and light weight without giving away too much performance to more sophisticated machines. The rigid spine frame also lent the Ala d’Oro and Ala Verde superior handling. Though not as reliable as they might have been (usually mechanical failure in the engine), the Aermacchis racked up some notable performances. Perhaps their most impressive result came in the 1964 Manx Grand Prix 250cc class, when four of the first six bikes home were Aermacchis.
It was clear further development was required, especially for the race bikes: for the 1966 model year, a bigger bore and shorter stroke (72mm x 61mm) gave 248cc and room for larger valves; an alloy cylinder replaced the iron item; the big end bearing became a double roller; the transmission gained one gear to make five; the camshaft ran on needle roller bearings; and the clutch was converted to run dry, making the race bikes easier to push-start — Le Mans style!
Now with much better reliability, the “dry clutch” five-speed 250s continued to be competitive in Europe, and the 344cc (74mm x 80mm) became a potent competitor in 350-class GP racing. Renzo Pasolini finished 3rd in the 350cc Grand Prix world championship in 1966 with Kel Carruthers repeating that achievement in 1968 mixing it up with the multi-cylinder might of Honda, Benelli and MV Agusta.
Aermacchis performed particularly well in the “Junior” Isle of Man TT, placing 6th in 1965, 4th, 5th and 6th in 1967, 4th and 6th in 1968 and with four machines finishing in the top ten in 1969. The 1968-on 350 featured new short stroke dimensions of 77mm x 75mm with 42hp @ 8400rpm.
Aermacchi would have liked to develop their engine into an overhead cam unit (and at least one prototype was built), but orders from Milwaukee decreed that the engine would stay OHV to make it suitable for AMA racing. And by the time the AMA rules were changed in 1969, it was too late, with Japanese two-strokes starting to dominate the smaller capacity classes. The H-D brand would go on to win four world championships in 250cc and 350cc classes between 1972-4 — but with two-stroke parallel twins, the Harley-Davidson RR250 and RR350 built by Aermacchi.
CR and CRTT
Meanwhile, Aermacchi produced limited numbers of race-tuned machines for U.S. flat-track and road racing, designated CR and CRTT respectively. These borrowed much engine technology from the Ala d’Oro racers, both the long stroke and (later) short stroke versions. They were especially popular in AMA Grand National championship racing, which included both dirt track and tarmac races. Apparently, the CR was never supplied complete from Italy, the rigid-rear frame being built in the U.S. Notable riders who developed their careers on CR/TTs included Cal Rayborn and Gene Romero.
Also developed for the U.S. market was an off-road machine, the CRS, or Competition Race Scrambler, typically fitted with a four-speed gear set for added durability in scrambles and other off-road competitions. MC
This story draws on information from Mick Walker’s books, Aermacchi Harley-Davidson Motorcycles and Mick Walker’s Italian Racing Motorcycles.
OHV vs OHC
Aermacchi never produced a “cammy” single except for a prototype double-overhead camshaft 250 racer, only two of which were built. It’s usually assumed that putting the camshafts in the cylinder head of a four-stroke engine is always desirable. But is it? Like most good questions, the answer is — it depends.
All other things being equal, getting more power from a motorcycle engine usually means more RPMs. More RPMs mean faster reciprocating engine parts — like the rockers and pushrods in an OHV engine, which have to change direction at a higher frequency. An overhead camshaft engine has no pushrods and typically no rockers either. That means reduced reciprocating mass. Given the same cam profiles and return spring pressure, an OHC engine should be able to spin faster without the valves “bouncing” or “floating.”
Both OHC and OHV also require strong valve return springs to suit race camshaft profiles. Ducati’s Desmodromic system gets around this issue by using cams to both open and close the valves. Theoretically, no spring is required, camshaft wear is reduced and the engine can use cams with a more aggressive profile for more power.
And while four-valve cylinder heads have been fitted to OHV engines (notably by Rudge-Whitworth in the 1930s), an overhead cam setup facilitates the use of a four-valve head. That usually means smaller valves, therefore with less inertia, again allowing higher revs.
Bianchi proposed a double-overhead camshaft head for the Ala d’Oro using the same bottom end and cylinder, and even commissioned a prototype. But Aermacchi’s owner, Harley-Davidson, scrapped the plan, believing an affinity existed between the Aermacchi OHV engine and H-D’s own OHV engines lent the latter a more sporting profile in buyers’ minds. Whether there was such a relationship is moot.
