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Specifications

Bore 

φ

32.0mm 

Stroke 

26.0mm 

Stroke volume 

20.9cc 

Weight (approx.) 

Main body : 690g / Muffler : 83g / Ignition system : 113g / Engine mount set : 156g 

Practical Speed 

Approx. 2,000-9,500rpm   

Applications

4-stroke 100~110class 

Propeller 

15”×8” ~ 16”×8”

Static thrust 

Approx. 3-4kgf 

Fuel 

Regular gasoline : Oil (2-stroke oil) =20:1 (Volume ratio) 

Fuel consumption 

Approx 15cc/min (At full throttle, approx 8,800rpm) 

*Fuel flow varies depends upon prop load. More fuel flow with larger load and less fuel flow with smaller load. 

Battery for ignition system 

Voltage:6-8V    higher than 1,000mA is recommended 

Accessories 

Instructions for SAITO

FG-21(AAC) 4-Stroke Gasoline Single Engine 

Thanks for buying SAITO FG-21 4-stroke gasoline engine

exclusively for model airplanes.

In order to avoid misuse, please be sure to read well the instructions 

carefully. If there should be any deficiency, inconvenience, etc.

concerning the manufacture, our company will repair them with responsibility. 

Any failure or trouble caused by unnecessary disassembly, modification, or other 

uses than those provided in the instruction manuals is not subject to the warranty, 

however.

Moreover, all responsibilities for the use of the engine, and other obligations and 

responsibilities based on laws, regulations, etc. are borne by the purchaser and the 

user, and SAITO SEISAKUSHO CO., LTD. is exempt from any responsibilities.

SAITO FG-21 is a 4-stroke gasoline engine exclusively for model airplanes which 

is designed with emphasis on high performance, durability, and weight saving. 

This engine is modified based on existing FG-20 gasoline engine, equipped with 

renewed ignition system. For the airplane on which FA-125 is installed, FG-21 can 

be replaced easily with minimal change such as fuel tank and lines to gasoline-

resistant ones. 

Features of FG-21

Cylinder 

 

The cylinder head is integrated with the cylinder in order to prevent distortion, save weight and improve 

cooling effectiveness. Hard chromium is plated the cylinder without using liners for higher durability.

Piston  

 

High-silicon-containing aluminum piston equipped with compression ring for higher performance.

Connecting rod  

Robust with forged high-strength aluminum. As a measure for gasoline engine, phosphor bronze busing is 

pressed into the big end to improve heat resistance.

Crankshaft 

 

Robust with forged chromium molybdenum steel and supported by two ball bearings.

Cam gear 

 

Placed in the front for compactification.

Cam   

 

High output type, high cam specification.

Combustion chamber  Volumetric efficiency and combustion efficiency are improved by adoption of a vent roof type combustion 

chamber.

Propeller nut   

Designed to have double nuts preventing loosening and fall-off for safety.

Exhaust sound   

Sound quality similar to the exhaust sound of the real airplane. And as calm as a glow engine.

Carburetor 

 

Self-designed and developed carburetor with a pump for small-seize 4-stroke gasoline engines.

Ignition system  

A new designed battery type electronic ignition and the electronic spark advancing system.

Starting method 

Forward rotation (CCW) can be manually started due to automatic spark advancing system. (Using a starter 

is still recommended for safety)

Fuel   

 

With the same composite fuel as two cycle gasoline engine which contains 5% of oil content.

Flight pattern   

Since there are no worries about the inclination of oil, all acrobatic flights are possible.

Spark plug 

 

Small-size spark plug dedicated for our 4-stroke engine, of which screw size is the same as that of glow plug 

(UNEF1/4-32)

Features of the gasoline engine

 Fuel efficient. 

 Low cost of fuel. 

 Easy to install “smoke system” (by using muffler pressure or crank pressure)

 The airframe could not be soiled easily.

1. 

Limit gauge (0.1t) for tappet adjustment 

1 pc.

2. 

Spanner for tappet adjusting lock nut 

1 pc.

3. 

Hexagonal wrench set 

 

 

1 set

4. 

Ignition system (with sensor attached) 

1 pc.

5. 

Spark plug  [SAITO SP-1] (attached) 

1 pc.

6. 

Plug wrench 

 

 

 

1 pc.

7. 

Muffler complete  

 

 

1 set

8. 

Engine mount set  

 

 

1 set

Summary of Contents for FG-21

Page 1: ...weight and improve cooling effectiveness Hard chromium is plated the cylinder without using liners for higher durability Piston High silicon containing aluminum piston equipped with compression ring for higher performance Connecting rod Robust with forged high strength aluminum As a measure for gasoline engine phosphor bronze busing is pressed into the big end to improve heat resistance Crankshaft...

Page 2: ...ommercial regular gasoline and reliable oil for 2 stroke In addition unleaded high octane gasoline is not neces sarily required for our engine Example of oil POWER LUBE KLOTZ ORIGINAL TECHNIPLATE KLOTZ GS RC model LUBE CASTROL POWER1 TTS Racing etc For the mixture ratio please be sure to use gasoline oil 20 1 or richer by volume ratio Any damage caused by the fuel used in which the oil ratio is lo...

Page 3: ...se capacity is higher than 3A Caution A gasoline engine generates a noise which has an adverse effect on RC adjustment unlike a glow engine Please be sure to carry out a noise check each time while the engine is running before the flight Since a noise which occurs during flight may lead to a large scale accident please carry out a noise check without fail As a simple method after starting engine y...

Page 4: ...sives such as screw lock on the tip of M4 cap screw to avoid loose ness when you install the engine To ensure that cooling wind passes through the engine and muffler the cowling should be devised Also make the air flow outlet larger than the inlet Building some baffles inside the cowling appropriately will enhance the cooling efficiency Insufficient cooling may cause engine trouble such as overhea...

Page 5: ...s set so that idling rotation may be 1800rpm to 2100rpm at the factory default However since it may vary depending on the condition at the time of operation adjust it so as to meet the operating condition For the slow needle s reference value refer to the figure in the section 7 In principle a carburetor is adjusted by first achieving peak the highest revolution with the main needle and then perfo...

Page 6: ... excessively the lock nut In the case of the engines for vehicle small gap is given to tappets to absorb valve elongation In the case of SAITO engines gap becomes larger during operations due to thermal expansion of the cylinder made of aluminum Therefore set the gap indefinitely close to zero while the engine is cold 8 When connecting the exhaust pipe to the cylinder or attaching the prop nut app...

Page 7: ... 27 1 2 85 Full throttle needle 1 Prop washer Nut Throttle barrel assembly 28 1 2 82 1 5 1 9 88B 89 Crankcase screw set Throttle lever 31 1 2 3 88B 90 1 Engine gasket set 89 Idle needle 1 32 1 2 3 4 5 6 8 Carburetor screw spring set 33 Cam gear housing 1 82 1 7 1 8 1 13 1 16 1 26 1 28 90 1 35 Cam gear 1 Carburetor gasket set 36A Cam gear shaft 1 32 4 5 6 82 1 9 1 14 1 18 1 20 1 22 91 1 37 Steel wa...

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