RCGF 120CC-Twin - User Manual

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Overview

Function Description
Important Technical Specifications
Usage Features
Maintenance Features

The RCGF 120CC-Twin is a 2-cycle piston valve type gasoline engine designed for model airplanes. This operator's manual provides comprehensive details for its installation, operation, maintenance, and troubleshooting.

Function Description:

The RCGF 120CC-Twin functions as a power plant for model aircraft, utilizing a gasoline-powered internal combustion engine. It is equipped with an electronic CDI (Computer Controlled auto advance, electronic ignition system) for reliable starting and consistent performance. The engine is air-cooled and designed for use with a propeller to generate thrust.

Important Technical Specifications:

Engine Type: 2-cycle piston valve type gasoline engine
Cylinder Displacement: 120cc (7.32 cu in)
Bore x Stroke: 1.85 in (47mm) x 1.38 in (35mm)
Carburetor: RCGF
Ignition System: DC-CDI (Computer Controlled auto advance, electronic ignition system)
Ignition Power Supply: 4.8-8.4V
Maximum Output: 12.5HP / 7600rpm
Speed Range: 1500-7600rpm
Fuel Mix Ratio: Pre-mixed Fuel, 25-40 (Gasoline):1 (recommended 30:1 for 90% high octane unleaded gasoline)
Recommended Fuel Octane: 87-93 Octane
Lubrication Oil: 2-cycle engine oil (high-quality synthetic 2-cycle oil recommended after break-in)
Recommended Propellers: 26X10, 26X12, 27X10, 28X10
Standard Propeller (Two leafs): 27X10 6580 rpm
Spark Plug: NGK CM6 Type (Cap size 0.018 in.—0.020in. <0.45mm—0.51mm>)
Cooling System: Air Cooled
Engine Weight: 5.69 lb (2580 g)
2xMuffler Weight: 7.05 oz (200g)
Ignition Module Weight: 5.11 oz (145 g)
Total Weight: 6.45 lb (2925 g)
Ignition Battery: 4.8-8.4 NiCd or NiMH, 6.6V LiFe or 2S LiPo pack
Idle Speed: 1600 rpm/min
Static Thrust: 59.7 lb (27 kg) @ 328 ft (100 m) altitude; 56.1 lb (25.4 kg) @ 5,900 ft (1800 m) altitude
Engine Length (back of mount to propeller washer face): 172 mm
Ignition Timing: Preset at 28-30° before Top Dead Center (TDC), adjustable from 26° (retarding) to 32° (advancing).

Usage Features:

The RCGF 120CC-Twin comes as a complete package including the electronic CDI ignition, muffler, spark plug, gaskets, bolts, throttle arm extension, and a manual.

Installation: The engine requires installation on a firewall at least 9.5mm [3/8"] thick, securely glued and reinforced. Fuel tank installation should use gasoline-approved components and either a 2-line or 3-line system. Non-metallic pushrods are required for throttle and choke. Electronic radio devices, including throttle and kill switch servos, should be installed at least 12" [305mm] away from the engine to prevent radio interference.
Propeller Installation: A drill guide is recommended for drilling the propeller to fit the hub. The manual provides a detailed method for drilling the center and outer holes if a drill guide is unavailable. The propeller should be mounted at the one o'clock position at the beginning of the compression stroke.
Engine Adjustment: The engine is factory preset, but minor adjustments to the carburetor's Low-speed Needle, High-speed Needle, and Idle Adjustment Screw may be necessary for optimum performance based on elevation. The ignition timing can also be adjusted.
- Idle Adjustment Screw: Clockwise increases idle speed, counter-clockwise decreases it.
- Low-speed Needle: Clockwise leans the fuel/air mixture at low speeds (default: 0.8 turns open from fully closed). Counter-clockwise richens the mixture.
- High-speed Needle: Clockwise leans the fuel/air mixture at high speeds (default: 1 turn open from fully closed). Counter-clockwise richens the mixture.
- Ignition Timing: Adjustable by sliding the ignition sensor. Advancing timing increases performance but also engine temperature and wear.
Starting Procedures: Two methods are described:
- Manual Starting: Requires a thick glove or heavy-duty starter stick. Involves switching ignition ON, closing the choke, opening the throttle slightly, flipping the propeller briskly until a popping sound is heard, moving the choke to OPEN, setting high idle, and flipping the propeller rapidly.
- Electric Starter Starting: Recommended for a 12-24V electric starter. Similar steps to manual starting but uses the electric starter to turn the engine over.
Safety Tips: Emphasizes paramount safety for the operator and others. Key warnings include: operating in a ventilated area, ensuring all components are secure, using a good quality screw sealant, installing on a shock-absorbing test stand during break-in, keeping onlookers away, using balanced propellers and lightweight spinners, never using damaged propellers, keeping foreign objects away, not starting on loose gravel/sand, not stopping the engine by throwing objects into the propeller path, securing fuel lines, using gasoline-approved fuel lines (not silicone), avoiding touching a hot engine, draining fuel before transport, and using high-quality 2-stroke oil.

Maintenance Features:

Fuel Filter Cleaning: The fuel filter in the RCGF Carburetor should be cleaned periodically to prevent miss-calibration of needle adjustments. This involves removing the Phillips head screw securing the carburetor filter cover and gasket, then cleaning the area around the filter with carburetor cleaner.
Warranty: The RCGF-120cc TWINs come with a two-year limited warranty through an RCGF service center, starting from the date of purchase. Retention of the receipt is required as proof of purchase.
Troubleshooting: A table is provided for common starting issues, including "Engine does not fire" (faulty battery wires, faulty spark plug, engine flooded) and "Engine starts, then rpm Increases till engine cuts out" (fuel not reaching engine), along with suggested diagnoses and fixes.
Optional Digital Tachometer: An optional Digital Tachometer can be connected directly to the ignition module (or via a Y-harness for older modules) to display engine RPM.