O.S. GT55 Gasoline Engine

Tower Stock# LXYNR4  •  Manufacturer Stock# 38000
O.S. GT55 Gasoline Engine (large view)
Notes from our tech department:
This is the O.S. GT55 Gasoline Engine with Electronic Ignition.


Produces 20-30% more power than any other engine in its class
IG-01 Capacitive Discharge Ignition uses a microcomputer programmed
for optimum spark advance through the use of magnetic sensors on
the crankcase and prop drive, the IG-01 also detects and
compensates for wet plugs to ensure consistent quick starts, also
requires minimum current in stand-by mode and features a low
voltage warning (intermittent engine operation)
Front mounted WLA-2 carburetor stays cooler for less heat
percolation and more consistent performance, simple and direct
throttle and choke linkages
Unique one-piece crankcase eliminates gaskets and enhances strength
and precision
Front induction rotary valve crankshaft design for positive opening
and closing of valve for optimum timing, no oil seal required which
eliminates RPM loss due to additional friction
Massive front and rear crankshaft bearings for longer life and
maximum power output
Thin high-performance piston ring and high-strength aluminum alloy
piston for reduced break-in and high compression from the very
first run
Two year limited warranty through Hobby Services beginning at date
of purchase


O.S. GT55 Gasoline Engine with Electronic Ignition, Carburetor, CM-6
Spark Plug, Prop Washer with four 5x40mm Socket Head Cap Screws,
Exhaust Gasket and Instruction Manual


Propeller: 22x8 for break-in
22x10, 23x8, 23x10, 24x8, 24x10 for sport/acro/scale use
Two-Cycle Oil: Break-In, Klotz Modelube recommended, mix at 30:1
gas/oil mixture for 10 flights, 1.3 - 1.6 gallons (5-6 liters) of
After Break-In: mix at 50:1 ratio, See COMMENTS below
Electric starter NOTE, The propeller must be brought up to at least
100RPM in order for the electronic ignition to work
Muffler: See COMMENTS below
Fuel: Unleaded regular gasoline (no need to use high octane)


Displacement: 54.9cc (3.35 ci)
Bore: 1.62" (41.2mm)
Stroke: 1.62" (41.2mm)
Output: 5.5 PS, 5.42 HP/7000 RPM
Practical RPM: 1,500 - 8,000
Weight: Engine 1,580g (55.7oz)
Igniter 140g (4.9oz)
Muffler 6.28oz (178g)
Carburetor Settings: Two turns out on high and low speed needles from
fully closed position, then start engine and follow break-in
instructions on pages 18-25 in manual

Distance/center of Mounting Standoff Holes Top to Bottom: 2.6" (66mm)
Distance/center of Mounting Standoff Holes Side to Side: 3.1" (78mm)
Distance/center/Mounting Standoff Holes/Crankshaft Center:1.3" (33mm)
Height/bottom of Mount to Top of Cylinder Head: 7.1" (180.4mm)
Height/center of Crankshaft to Top of Cylinder Head: 5.5" (139.2mm)
Width at Cylinder Head: 2.9" (75mm)
Center of Crankshaft to Center of Exhaust Outlet: 2.9" (74.6mm)
Length from Mount to End of Drive Spacer: 5.9" (150mm)
Length from Mount to Crankcase Center: 1.5" (37.5mm)
Thread size of pilot shaft for spinner bolt 5mm


If using a different brand of oil other than Klotz, OS recommends
their own mix ratio which may differ from the manufacturers'
For 40:1, and 50:1 oils, OS recommends a 30:1 gas/oil mixture

25:1 is 5oz of pre-mixed 2-cycle oil or 151 ml per gallon of fuel
30:1 is 4.3oz of pre-mixed 2-cycle oil or 126 ml per gallon of fuel
40:1 is 3.2oz of pre-mix 2-cycle oil or 95 ml per gallon of fuel
50:1 is 2.6oz of pre-mix 2-cycle oil or 76 mll per gallon of fuel

The following mufflers are ideal for different applications;
J'TEC Large Wraparound Pitts Muffler for inverted
mounting applications.
Bisson Wraparound BISG9250, and Inverted mufflers will
also fit.
Slimline offers the following, #2125 Inverted Pitts Muffler,
#2156 Side Canister, and #2155S w/Smoke System.

jxs 10/15/09
updt jxs 03/17/10
updt jxs 04/20/10
updt jxs 10/12/10
updt jml 10/11/11

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