O.S. FS-120 III Surpass Ringed 4-Stroke w/Pump

Tower Stock# LXBY65  •  Manufacturer Stock# 35540
O.S. FS-120 III Surpass Ringed 4-Stroke w/Pump (large view)
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Notes from our tech department:
This is one of the O.S. Surpass series of 4-stroke model engines.
The Surpass series is the 2nd series of 4-stroke engines (The 1st series was
the FS series, discontinued and replaced by the Surpass series around 1986-7).
"Surpass" refers to this series gaining 30% more power than the previous
FS series.


Specially developed PD-07 pump
New 70N carb
Ball bearing-supported camshaft and crankshaft
New F-5020 Silencer
Two year warranty


One Assembled Engine w/Carburetor and #F Glow Plug
One Muffler w/Manifold
One Set of Instructions, O.S. Poster, and Decal
(Mounting Template Is No Longer Included per O.S.)
One additional coarse needle for less sensitive carb adjustment.


Fuel: 5%-15% nitromethane with 18% lubricant. Synthetic, castor, or
a synthetic/castor blend may be used.
NOTE: Certain four-cycle fuels cannot be used due to low oil content.
However, SOME four-cycle fuels such as the Wildcat 4-Cycle 15%
(CATP9109) may be used because it has 18% oil content.
When choosing fuels for this engine, the modeler must be sure to
select a fuel with at least a 18% lubricant content.
Starting and Field Equipment.
Propeller (see SPECS)


Bore: 30.4mm (1.20")
Stroke: 27.5mm (1.08")
Power Output: 2.1 PS, 2.07 HP at 12,000 RPM
Practical RPM Range: 2,000 - 12,000 RPM
Weight-Without Muffler: 32.5oz (921g)
Weight-With Muffler: 35.3oz (1000g)
Crankshaft Thread Size: 5/16-24
Valve Clearance: Between .04mm and .1mm (or between .0015" and .004",
measured between the valve tip and rocker arm)
Length: 102mm (4.09") from backplate to the front of the drive washer
Width: 47mm (1.85") width of engine neglecting the mounting flanges
58mm (2.28") distance between the mounting hole centers
Height: 139.5mm (5.49")
Suggested Prop(s): 14x9, 14x10, 14x11, 15x8, 15x9, 15x10, 16x6,
Construction: Aluminum and Aluminum alloys

Needle Settings: High Speed: 1.5 turns out from fully closed
Low Speed: 2.5 turns out from fully closed with the
throttle fully closed


Some differences between 2-Stroke and 4-Stroke engines:
4-Strokes are quieter.
4-Strokes get better Fuel Economy
2-Strokes generate More RPM (11,000-13,000 RPM with prop
and 4-Strokes rev to around 9,500 RPM)
4-Strokes generate much more torque and will swing a larger prop.
4-Strokes have a more realistic sound, like a real aircraft engine.

The new Surpass engines (Version II and III) have more power than
their predecessors and they also have more corrosion prevention
on the inside of the crankcases.
5-7-97 djg
updt lmm 3/31/09

See Tower Catalog page 172.
Easy RC: Engines
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