O.S. FR7-420 Sirius

Since 1986, O.S. owners have enjoyed the unique experience of owning and operating the fabulous FR5-300 Sirius 5 cylinder radial. Models have become bigger over the years and O.S. wanted to release a new radial engine to cater for that market. The result is the gorgeous FR7-420. With 7 cylinders and a capacity increase to nearly 70cc, the FR7-420 offers a dramatic increase in both torque and power. In keeping with the scale image set by the Sirius, the new FR7-420 has been styled in the same way with front pushrods and separate rocker boxes for the inlet and exhaust valves. These totally new cylinder heads are not just about ‘style’, they offer a more efficient design that contributes to the power output. That neat frontal appearance is maintained by keeping the single, dual needle carburettor at the back and hidden in the centre of the engine mount. The prototype engine shown here will have some detail changes (cast cylinder heads etc) made before release, but the general style will be similar. It would almost be a crime to hide it away in a cowling!

Quality and style this good is something to be proud of owning. The wide range of large propellers recommended makes choosing the right one for your model simple. At these sizes, they could be close to scale!

Specifications
Weight	3167g (111.71 oz)
Propeller Range	22x10-12, 23x8-12, 24x8-12, 26x8
Displacement	7x 9.95cc (0.607")
Bore	24mm (0.945")
Stroke	22mm (0.866")
Practical RPM	1500 - 7000 rpm