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Saito FG-21 Instructions Manual

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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,
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 the gasoline engine
・ Fuel efficient. ・ Low cost of fuel.
・ The airframe could not be soiled easily.
Features of FG-21
Connecting rod
Cam gear
Combustion chamber
Propeller nut
Exhaust sound
Ignition system
Starting method
Flight pattern
Spark plug
Weight (approx.)
Practical Speed
Fuel consumption
Battery for ignition system Voltage:6-8V higher than 1,000mA is recommended
Instructions for SAITO
・ Easy to install "smoke system" (by using muffler pressure or crank pressure)
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.
High-silicon-containing aluminum piston equipped with compression ring for higher performance.
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.
Robust with forged chromium molybdenum steel and supported by two ball bearings.
Placed in the front for compactification.
High output type, high cam specification.
Volumetric efficiency and combustion efficiency are improved by adoption of a vent roof type combustion
Designed to have double nuts preventing loosening and fall-off for safety.
Sound quality similar to the exhaust sound of the real airplane. And as calm as a glow engine.
Self-designed and developed carburetor with a pump for small-seize 4-stroke gasoline engines.
A new designed battery type electronic ignition and the electronic spark advancing system.
Forward rotation (CCW) can be manually started due to automatic spark advancing system. (Using a starter
is still recommended for safety)
With the same composite fuel as two cycle gasoline engine which contains 5% of oil content.
Since there are no worries about the inclination of oil, all acrobatic flights are possible.
Small-size spark plug dedicated for our 4-stroke engine, of which screw size is the same as that of glow plug
Main body : 690g / Muffler : 83g / Ignition system : 113g / Engine mount set : 156g
Approx. 2,000-9,500rpm
15"×8" ~ 16"×8"
Regular gasoline : Oil (2-stroke oil) =20:1 (Volume ratio)
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.
Limit gauge (0.1t) for tappet adjustment
Spanner for tappet adjusting lock nut
Hexagonal wrench set
Ignition system (with sensor attached)
Spark plug [SAITO SP-1] (attached)
Plug wrench
Muffler complete
Engine mount set
4-stroke 100~110class
Static thrust
Approx. 3-4kgf
1 pc.
1 pc.
1 set
1 pc.
1 pc.
1 pc.
1 set
1 set
Stroke volume


Table of Contents

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   Summary of Contents for Saito FG-21

  • Page 1 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.
  • Page 2 Outside dimensions Mechanism of 4-Stroke Engines 4-Ø4.2 63.5 13.7 The 4-Stroke engine provides 4 individual piston movements as illustrated below. The “Stroke” means the piston movement from the Top Dead E.C. Center to the Bottom Dead Center. In the 4-Stroke engine, one cycle of operation in change of gas state inside the cylinder and valve movement are completed at every 4 strokes of piston that is every...
  • Page 3 (1) Plug cord (meshed high tension cord) The tip of the plug cap is designed exclusively for SAITO SP-1 Plug. When you put on the plug cap, insert it to the plug until the clip fits the groove on the plug (Fig.6; then you will hear clicky sound) to avoid coming off during flight. And then pull the plug cap to make sure that it won’t come off.
  • Page 4 6. Spark plug SAITO SP-1 spark plug is the standard equipment. Dimensions are as follows; Hexagon width: 8mm Screw size: UNEF 1/4-32 Reach (with a washer): 5.5mm Spark-gap: 0.4-0.5mm For replacement, please specify “SAITO SP-1”. Since our four cycle engine uses a mixed gasoline, please decide the numbers of flights by yourself and clean the spark plug. Please replace, when it is degraded.
  • Page 5 (10) Prepare a fuel pump for gasoline. (Be sure to attach a filter to the intake port. It is available as an option.) (11) In order to check discharge of the breather, attach a heat-proof and gasoline-proof transparent tube. (12) Prepare a battery for the electric starter. Caution: If there’s anyone stands forward, be sure to have them move behind the airplane prior to start the engine.
  • Page 6 * 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.
  • Page 7 SAITO FG-21 Parts List No. Description Q'ty No. Description Q'ty 01 Cylinder Valve set (In & Ex) 1set 06 Piston 46-1,-2 07 Piston pin Valve spring & Keeper & Retainer 2ea. 08 Piston pin retainer 47-1,-2,48 09 Piston ring 48 Valve retainer (Cotter)

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