O.S. 91FX Airplane Engine Ringed w/Muffler

Tower Stock# LXBY47  •  Manufacturer Stock# 19021
Notes from our tech department:
This is one of the O.S. FX Series of High-Performance Engines. This series of
engines is Used in Sport and Aerobatic Aircraft. The FXs are Designed to
Use a Muffler or Tuned Pipe. This Ringed engine has a steel liner.


One-piece crankcase
Twin ball bearing-supported crankshaft
Schnuerle porting (AKA Schnuerle scavenging)
Aluminum piston, steel cylinder liner and iron piston ring
Side exhaust with muffler with rotatable exhaust outlet
Carburetor with remote needle mounted on the engine back plate
(to keep fingers away from the spinning propeller).
Two-year warranty


One Expansion style muffler (E-4010) with screws
One Assembled engine with carb.
One package illustrated instructions, parts list, and O.S. decal
One O.S. 8 glow plug (OSMG2691)


Displacement: 14.95cc (0.912 cu in)
RPM range: 2,000 - 16,000
Bore: 27.7mm (1.090)
Stroke: 24.8mm (0.976)
Compression Ratio: 10.1 : 1
Weight: 550g (19.42oz) 24.3oz wmuffler
Horsepower: 2.8 BHP at 15,000 RPM
Length: 96mm the distance from the backplate to drive washer
Width: 42.6mm width of engine neglecting engine mounting flanges
52mm distance between centers of the mounting holes
Height: 103mm
Crankshaft Thread Size: 516-24
Props: Hobby Services recommends a 13x8 or 13x9 prop (699)
NOTE: Exh port same size as .61SF so can use 61SF Header w91 Pipe

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)


Fuel: 18 (minimum) conventional lubricant content and 5-20 Nitro.


All FX series engines are covered by the O.S. two year warranty
Engine mounting & exhaust dimensions are the same as .61FX.
Engine guru Clarence Lee tached this engine wvarious props
Prop Size RPM
13x6 12,500
13x8 10,400 using a 13x8 prop,
13x10 9,500 Hobby Services tached this
14x6 10,900 engine at 11,300 RPM
14x8 9,500 6-24-99
14x10 8,400
15x6 10,200
15x8 8,100
16x6 8,300


O.S. now uses an updated Back Plate (Cover Plate) and Needle
Valve setup for this engine. It now uses the following:
29057000 COVER PLATE 91SX-H
- OSMG6997 26582900 VALVE ASSY 40-65LA
- OSMG7152 26582931 NEEDLE STAY 91FX
WLG 10-16-98
updated 051004 tjt
updt jxs 101705
updt lmm 32709



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