Yankee 500 Z
By Phil Aynsley
The Yankee 500 Z was the product of the Yankee Motor Company based in Schenectady, New York. Founder John Taylor was the US Bultaco importer in the early ‘60s, then the Ossa importer, so turned to them when he decided he wanted to produce what would, decades later, be known as an adventure bike. The prototype was first shown in 1967 but it took until 1971 for production to begin.
The bike was very much a US/Spanish collaboration. The well known American racer Dick Mann designed the TIG-welded frame, which was made from the very exotic at the time 4130 chrome-moly steel. Smith and Wesson produced the forged triple-clamps.
Conceptually the 488 cc motor was basically two Ossa Pioneer 250 cc singles siamesed together, although the actual engineering wasn’t that simple with an extremely robust crankshaft assembly and complex primary drive that had a four-row chain driving a jackshaft then a gear drive to the dry clutch.
The most unusual aspect of the motor however was that the standard 360º crankshaft timing could be fairly easily changed to a 180º firing order if the rider preferred. To accommodate this feature two 6V Motoplat alternators were fitted (one on each side of the motor), together with two seperate coils for the electronic ignition.
Lubrication was by pre-mix and output was 40 hp but around 70 hp was possible with the factory supplied optional exhausts and carburettors.
The innovation didn’t stop with the motor, the swing arm used oval section 4130 tubing and the rear disc brake was the first fitted to a production off road motorcycle.
A six-speed gearbox was used, while another example of Taylor’s drive to produce an exceptionally rugged and well built machine was the fitment of 42 mm front forks (by the Spanish firm Telesco), when 35 mm units were the norm at the time.
The penalty for all this ruggedness was a weight of 158 kg (with half a tank of fuel). Together with the devaluation of the US dollar at the time (which doubled the cost of the imported components), the result was only 760 Yankee 500 Zs were produced over a two year period.
Back in Spain Ossa, being stuck with their newly developed motor, built a road going version known as the 500SS. Output was increased to 58 hp at 7,500 rpm by using cylinders with port timing from the Stiletto motocrosser, larger 32 mm carburettors and much more free-flowing exhaust system.
The 500 Z’s frame design was used with suitable modifications, although in mild steel, not chrome-moly. A 12V electrical system replaced the Yankee’s 6V system. A single Brembo disc brake was fitted to each cast alloy wheel. Weight was 180 kg. Not many were produced and they are quite a sort-after rarity now.
Source: MCNews.com.au