O.S.SPEED R21 Euro 3
The R21 Euro 3 is the next step in O.S. Engines' successful R21 series. It builds on proven parts from the Euro 2 and R2106, with a newly developed piston & sleeve, combustion chamber and carburetor focused on throttle response, heat management and reliability. The result is an engine that responds instantly and delivers consistent performance, heat after heat.
Crankcase with ceramic bearings
The engine uses the proven crankcase from the R21 Euro 2, fitted with ceramic ball bearings for low friction, eager revving and long service life.
R2105 crankshaft with tungsten weights
The R2105 crankshaft has two tungsten counterweights (Ø 4.5 mm). They optimise balance and give noticeably sharper throttle response out of the corners.
Newly developed piston & sleeve
The cylinder sleeve has a newly designed structure with excellent overall balance across the rev range. The piston is the same as in the R2106, but has a special treatment that improves resistance to seizure. This gives larger safety margins when the engine is working hard.
Combustion chamber with redesigned cooling fins
The cooling fins of the combustion chamber have been redesigned for better heat dissipation, so the engine holds a more stable operating temperature throughout the race.
Outer head with new laser logo
The outer head keeps the signature black O.S. SPEED finish, now with a newly designed laser-engraved logo.
21M5(B) carburetor with dust cover ring
The carburetor has a dust cover with a dust cover ring. It prevents fuel leakage and stops air getting into the fuel line, which makes tuning more consistent and predictable.
Proven technology from the R2106
All other internal parts are identical to the R2106, so you get proven reliability and good spare parts availability.
Highlights
- Ceramic ball bearings for low friction and long service life
- Crankshaft with tungsten weights for quicker throttle response
- New cylinder sleeve and specially treated piston with improved seizure resistance
- Better heat management thanks to new cooling fins on the combustion chamber
- Carburetor with dust cover ring against fuel leakage and air in the fuel line
- Shares parts with the R2106 and R21 Euro 2
