O.S. 25FX ABL w/Muffler .25 Airplane Engine

Tower Stock# LXBY42  •  Manufacturer Stock# 12660
O.S. 25FX ABL w/Muffler .25 Airplane Engine (large view)
Notes from our tech department:
O.S. has Updated the .25 SF with this New High-Performance .25 FX.
This Engine may be used in Sport and Aerobatic Aircraft. The FX is Designed to
Use a Muffler or Tuned Pipe. Comes with a 2-Year Warranty.


Remote Needle Attached to the Backplate keeps fingers away from prop
Twin Ball Bearing-Supported Crankshaft
Schnuerle Porting (Schnuerle scavenging)
Advanced Bi-Metallic Liner. This process uses a double layer of
plating material, rather than one thicker layer. This helps the
metal to bond to the cylinder, and is more durable. Also, the
plating process is more consistent, resulting in a more precise
fit between piston and sleeve, for better compression, longer life.
Side Exhaust
One-Piece Crankcase


One Expansion Style Muffler
One Set of Instructions, Decal, and Poster
One Assembled .25 FX w/Carb


Displacement: 4.07cc (.2485 cu in)
Bore: 18mm (.708")
Stroke: 16mm (.630")
Horsepower: .84 BHP at 18,000 RPM
Weight: 248g (8.8oz) 10.8oz w/muffler
Length: 75.6mm (2.98") distance from the backplate to drive washer
Width: 30mm(1.18") width of engine neglecting engine mounting flanges
38mm (1.50") distance between centers of the mounting holes
Height: 75.5mm (2.97")
Crankshaft Thread Size: 1/4-28
Recommended Props: Pattern Flying: 9x5, 9x6
Pattern Flying if a tuned pipe is used: 9.5x5
Sport Flying: 9x5, 9x6, 9.5x5, 10x4, 10x5
Practical RPM Range: 2,500 - 19,000 RPM

High Speed Needle: 1.5 - 2 turns out from fully closed
Low Speed Needle: 2mm gap between the needle and spray bar at full
throttle (looking down the neck of the carb)


Long Glow Plug (O.S. #8 recommended OSMG2691)
Fuel with 18% (minimum) lubricant content and 5%-15% Nitromethane
(All 5%-15% fuels we carry meet these requirements)
updated jpg 9/20/05
updt lmm 3/27/09

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