REVERSE CYLINDER, EFI, TWO-STROKE OSSA IS BACK: With A Fuel-Injected, 272cc, Reverse Cylinder, Two-Stroke Engine; It’s Not Ready For Motocross Yet, But It Is A Cool Design

November 19, 2009
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MISSING IN ACTION SINCE 1985: OSSA IS BACK:
WITH A FUEL-INJECTED, 272CC, REVERSE CYLINDER, TWO-STROKE ENGINE; IT’S NOT READY FOR MOTOCROSS YET, BUT IT IS A COOL DESIGN

Remember the Stiletto? Phantom? Pioneer? Explorer?


The Phantom.

Way back in 1967, Ossa sales manager Eduardo Werring contacted John Taylor to see if he would help the Spanish manufacturer enter the United States market. Taylor, who was responsible for the success fo Full Bore boots in America, agreed to take on the Ossa brand.

Ossa’s were sold in America all through the 1970s, but by the ?80s Ossa had faded from the U.S. scene and by 1985 Ossa closed its doors for good.

They are back! Once best known in the USA as the bike that Marty Moates raced motocross on and Mick Andrews rode to trials glory, Ossa has decided to re-enter the motorcycle market with a trials bike?the TR 280i. Ossa has worked on redistributing the various parts of the bike logically in terms of their weight distribution (a la the Yamaha YZ450F).


The fuel injection is downdraft from the front, while the cylinder is tilted rearwards. The exhaust come out the back of the cylinder.

Parts such as the fuel tank, air filter box and radiator have been positioned with the needs of the bike in mind. “Having the air filter at the bottom of a trial bike with the fuel tank high up or located next to the exhaust are concepts that do not make sense from our point of view,” says Josep Serra , the Ossa project manager. So OSSA’s engineers approached the design of the new Ossa TR 280i by putting the various parts of a motorcycle on the table and taking a blank sheet to design and redistribute them based on their needs.

The fact that the new TR 280i has an electronic-injection system has enabled Ossa’s engineers to redistribute various parts without being constrained by the position of the traditional carburetor. “Sometimes the injection system has been put in the same place as the carburetor would have gone, with the fuel tank at the top of the bike, without considering the option of finding a new position for it. Ossa factory let me start from scratch and that was a determining factor in taking on this project,” said Josep Serra.


The right side of the engine show the compact cases, water pump, clutch and fan-assisted radiator.

The new two-stroke engine is very compact with a single-piece crankcase. The gear change extends out of the right-hand side and the crankshaft is opposite it on the left. Since the engine cases act as the chassis, since it is the toughest part of bike, it has been possible to make a compact block. This simplifies the possibility of access to gear ratios.

Another important aspect is that it is cheaper to maintain since it is really straightforward to work on the engine. It can be considered a conventional engine in terms of geometry or thermodynamics, but Ossa managed to design a highly compact unit. It is one of the smallest engines around.


The exhaust pipe exits above the chain and dumps into a collector.

The 3-liter fuel tank has been positioned where the radiator has traditionally gone on trial bikes in order to improve the weight distribution. Placing the radiator behind the fuel tank and filter box prevents the radiator from getting covered in mud (a fan was fitted for low-speed riding).

Also, by inverting the cylinder Ossa was able to fit the inlet practically vertically behind the fuel tank, so the air comes in through the filter at one of the highest points on the bike. This makes the filter better isolated and it is much simpler to get at the filter itself through a cap. Some parts of the injection system are fitted inside underneath the cap. There the parts are not affected by either the engine itself or humidity.

OSSA TR 280I ENGINE SPECS
Capacity…272.2 cc
Type…Two-stroke, single cylinder, case-reed intake directly into the crankcase.
Cooling system…Liquid-cooled.
Bore x stroke…76×60 mm.
Fuel supply…EFI Kokusan battery-less system.
Ignition…CDI Kokusan digital magnetic flywheel.
Clutch…Hydraulic.
Gear box…Six-speed.

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