Ossa Stiletto 175 And 230
THE ULTIMATES:OSSA STILETTO 175 AND 230
Sophistication for Dynamic Competition
UGLINESS is a trait that a great many off-road competition bikes display lavishly. Their inelegance has something to do with their fat, lumpy tires, spindly front fenders poking skyward, and a general air of nuts, bolts and sprockets. Cobby, the British would say. Ossa, however, is one company that refutes the idea that finish and appearance don’t count on racing machinery. The Spanish factory’s 175and 230-cc Stiletto scramblers are two of the most handsome bikes to be seen on any track, yet they sacrifice nothing in terms of handling, power, and competitive performance.
Some excellent work with fiberglass accounts for the lissome lines of both machines. The tank and seat units are smart one-piece moldings, that incorporate something of a streamlined effect. Front fenders, and the paneling around the Ossas’ mid-sections, also are formed of weight-saving fiberglass. The glasswork itself shows a high degree of craftsmanship, with no ragged or stringy edges to mar its quality. Each tank holds 2.6 gal.
Paintwork, too, is well applied, and, on the test bikes, showed a marked refusal to fade or chip. Two color schemes are available—one features a silver frame with red and metalflake silver bodywork, and the other sports a black frame with blue and gold fiberglass sections. The combinations are bright without being garish, and reflect a knack among Spanish factories for offering harmony of components and pleasing colors.
The 175 was set up primarily for TT racing, and its equipment included trials type rubber at both ends, with a 3.50-19 front wheel and a 4.00-18 rear size. Together with a rather narrow handlebar, this arrangement makes for less than satisfactory handling in true motocross going, but the bike is superb on a fast, “slidy” type circuit. Ossa offers the customer a choice between the 19-in. front wheel, or a 21-in. in size. The 230 was fitted with one of the latter tires, and was a genuine motocross tool. The exhaust pipe runs under the machine, instead of high on the left, as on the 175, and at its lowest point is only 6 in. above the track surface. But this point occurs just in front of the rear wheel, so there ' is little chance of it suffering damage. The larger front wheel, and a handlebar offering more leverage, convert the 175 into an equally good mount for motocross.
Footrests on both machines are well designed, and feature a large diameter pivot area, and plenty of room for even the biggest boot to find plenty of parking space. The pegs are spring loaded at the classic 45-degree angle, and prove satisfactory in all kinds of terrain.
No sign of flexing could be detected from the duplex frames, while the bikes steer well at all angles of lean. The swinging arms are solidly constructed from oval section tubing. Mounting points for the shock absorbers vary slightly between the two bikes. The 230 units are fixed close to the rear axle, giving them a rakish forward angle. They are mounted on the swinging arms in full “U” brackets, while the 175 versions are located by a single tab, attached to the inner edge of the arms. Wheelbase of the 250 measures 54.5 in.; the figure is 1 in. less for the 175.
A singular mystery occurs with the gearbox. The three lower gears engage faultlessly, but, under hard riding, fourth would occasionally slip out, resulting in the wild scream of a racing two-stroke set free. This could only be avoided by concentrating on pushing the lever fully home, which could be a hindrance during hectic racing conditions. Clutch action is light and consistent. After a series of full bore starts, the clutch still released fully, engaged at the identical point of lever travel, while the primary case offered no indication of the heat it was hiding. A bonus point here is the cable hookup. The lower end stands out in the open, with the operating arm exposed. Thus, a change of cable can be made in seconds.
Both machines feature similar engines—the differences are that in the 175 unit, bore is reduced from 70 mm to 60.9 mm. In both units, piston stroke is identical, at 60 mm. The larger engine employs a 32-mm IRZ carburetor, while the 175 breathes through a 27-mm Spanish Amal instrument. Both engines display a pleasing degree of quality construction. Each connecting rod is carried on a needle bearing at its small end, and by a caged roller bearing at the lower end. Full circle flywheels are pressed onto the crankpin at 15 tons working pressure, to insure prolonged alignment, and the big end is given a considerable degree of side clearance, to allow for maximum lubrication. The gearbox mainshaft is supported at one end by a double-row needle bearing, and at the opposite end by a ball bearing, while the multi-plate clutch turns on a needle bearing. The nickel steel gears are actuated via a rugged shifting drum arrangement.
Compression ratio is high, at 13.7:1. The alloy barrel—matched with an iron liner—is finished in black paint on its outer surface, for maximum heat dissipation. Ossa’s theme of good looks for the Stilettos is maintained by the polished alloy outer cases, branded on the right side with a large, smart “Ossa” stamp.
During one of the test sessions, the Stilettos were matched in a series of off-road drag races with other motocross machines of both 250 and 360 cc displacements. The larger Ossa stayed with the 250s, and only lost out to the 360 in the higher gears. The 175 obviously was a little slower, but is fully competitive, making allowance for its disadvantage in cubic inches.
Brakes are 6.2 in. in diameter, front and rear, and are powerful enough to haul the Ossas to a swift halt without any hysterics. Cable operated rear brakes can be a little inconsistent during wet or freezing weather. This system is used perfectly on both Stilettos. Anyone who buys one of the bikes with the intention of trying some truly serious competition work, will probably wish to modify the riding position. The seats could be larger, with a less exaggerated taper to the forward sections. The rider can too easily slide ahead of the cushion and bump down hard on the tank. Footpeg location also could be better. The standard setup places them too high in relation to the seat, so that standing tends to become a bind after only a fairly brief session. Improvements should be directed toward allowing the pilot to stand and crawl about the machine with more ease.
Sophistication is apparent in the Stilettos, not only in their finish, but in such bonuses as an electronic ignition system that eliminates points (thus, the engine permanently retains correct timing), Akront alloy wheel rims, and Timken taper roller steering bearings.
Up to now, some people have pondered over the somewhat odd piston displacement of 230 cc on Ossa’s larger engine, and concluded that the unit must be at a disadvantage against full 250-cc machines. This assumption is far from being correct, as the factory’s competition record proves. The little 230 Singles frequently have bested full 2 5 0s, in a variety of events from observed trials to world championship road racing (as an example of this, Santiago Herrero recently rode the works entered 230 to 3rd place in the 250 class of the Italian Grand Prix, beaten only by two four-cylinder Yamahas). However, to dispel any final doubts about the Ossa’s power, the factory now offers a conversion that enlarges the engine to 244 cc. The kit comprises an additional cylinder and piston, with all the parts necessary for installation, and is included in the $800 p.o.e. price tag of the 230 Stiletto. Thus, a customer can compete with either engine displacement.
The 175 machine is priced at $725 p.o.e. The factory also says that, early in 1969, a 125-cc Stiletto will be available. This bike will be almost identical to the larger ones, and should make a dynamic contribution to the fast developing small bike racing classes. [o]
