This is the Magnum XL .30 RFS Four-Stroke Airplane Engine.
Steel sleeve and ringed piston for long life. Rotatable muffler to match appearance and installation requirements of specific aircraft. Dual ball bearing-supported crankshaft. Dual needle carburetor.
Break-in Prop : 9 x 5
Displacement : .30 cu in (5cc)
Bore : 19.7mm
Stroke : 16.4mm
Practical RPM : 2,000-13,000
Weight : 9.6 ounces
Crankshaft thread size : 1/4 - 28
Distance between left and right mounting holes : 1.41 in. (36mm)
Distance between front and rear mounting holes : 0.55 in. (14mm)
Distance from rear of engine to front of drive washer : 3.34 in. (85mm)
Height/bottom of crankcase to top of cylinder head : 3.30 in. (84mm)