The biggest single cylinder engine made by O.S. so far is the first O.S. engine for many decades to be spark ignition using petrol as a fuel.
O.S. have started from the ground up and built a completely new engine with the GT55. The styling is unmistakably O.S. yet draws on their extensive experience in engine design to keep weight to a minimum and power, torque and cooling to a maximum.
Those deep crankcase and cylinder head fins are designed to provide maximum cooling across the entire RPM range. The mounting lugs have been position to be compatible with the pattern used by the most popular engines on the market, making fitment very easy. That front mounted, Walbro carburettor helps to keep the mounting standoffs short and therefore limit vibration. The front carburettor also makes simple installation in both scale and aerobatic models. Throttle response is instant and progressive, making fine throttle stick inputs noticable and controllable, a great feature for those that want to prop hang!
The CDI ignition system enables quick starting, good throttle response and a steady, low idle. It provides high voltage at high RPM to control misfires as well. There is a built-in function to warn of low battery voltage by varying the throttle. The durable, magnetic sensing system is precise enough for accurate understanding by the CDI unit of the timing requirement at all throttle settings.
Inside, there is a tough rotary port crankshaft running in precision bearings (the front is rubber sealed). The roller bearing big end in the CNC machined conrod transfers the piston load to the crankshaft efficiently and effortlessly. In turn, the light, CNC machined piston (with single ring) moves inside a plated cylinder that has been optimised for the operating RPM range and the throttling characteristics required.
The propeller driver uses a central locating shaft and four radial bolts in the same pattern as many popular engines on the market. The same goes for the exhaust port mounting bolt holes, making for ready access to the various scale and sports mufflers already on the market.
With 55ccs of O.S. power on tap, is there a better choice?
|Weight:||1580g (55.07 oz) Eng/140g (4.94 oz) CDI|
|Practical RPM:||1500 - 8000 RPM|| |