O.S. 120AX Special Engine

Tower Stock# OSMG0652  •  Manufacturer Stock# 19215
O.S. 120AX Special Engine (large view)
Notes from our tech department:
This is the 120AX Special Ringed Aircraft Engine from O.S. Engines.


High performance two stroke engine designed for sport and scale
Compact size enables it to fit into most cowls
Crankshaft port timing was modified to increase power at high RPM
Velocity stack on carburetor adds acceleration at high RPM
0.1mm head gasket increases compression ratio for more power
1mm deeper machining to enlarge intake port for greater RPM
Two year limited warranty through Hobby Services beginning at date of


120AX Special Ringed Aircraft Engine, #8 Glow Plug, 70D Carburetor
with Velocity Stack, Instruction Manual, Prop Washer & Nut and
Needle Valve Extension Set


Fuel: Two-Stroke with 18% lubricant and 5-20% nitromethane
Muffler: E-5020 "Power Box"
Propeller: 15x10-12 or 16x8-10


Displacement: 1.218 cu in (19.96 cc)
Bore: 1.197" (30.4mm)
Stroke: 1.083" (27.5mm)
Practical RPM Range: 1,800 - 9,500
Output: 3.35 PS (3.155 HP) @ 9,500 RPM
Crankshaft Size: UNF5/16-24
Distance between Mounting Hole Center Same Side: 0.98" (25mm)
Distance between Mounting Hole Center Opposite Side: 2.3" (58mm)
Height/bottom of Mounting Tab/top of Cylinder Head: 3.4" (85.7mm)
Height/bottom of Crankcase/top of Cylinder Head: 4.3" (109.2mm)
Length from Backplate to front of Drive Hub: 3.9" (100.2mm)
Length from Backplate to end of Crankshaft: 5.5" (139.9mm)
Length from Backplate to Center of Crankcase: 1.2" (30.4mm)
Length from front of Drive Hub to end of Crankshaft: 1.6" (39.7mm)
Width at Mounting Tabs: 2.6" (67mm)
Width of Crankcase below Mounting Tabs: 1.8" (46.5mm)
Height from Crankshaft Center to Needle Valve: 1.3" (33.8mm)
Distance between Muffler Mounting Hole Centers: 1.9" (48mm)
Carburetor Settings;
Needle Valve, 2 - 2.5 turns out from fully closed as a starting
Mixture Control Valve, Close throttle rotor and screw in Mixture
Control Screw until it stops, then unscrew approximately 3/4 turn.
NOTE, Mixture Control Valve is factory set and should require only
small adjustments. Refer to instruction manual for full break-in

jxs 06/11/12

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