Great Power Engine GP123 V2

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Summary

Technical Specifications

Single-Cylinder Engines

Provides detailed technical specifications for single-cylinder GP engine models.

Twin-Cylinder Engines

Provides detailed technical specifications for twin-cylinder GP engine models.

This document is an instruction manual for Great Power Engines, a series of two-stroke internal combustion engines designed for model aircraft. The manual provides detailed technical specifications, safety instructions, operational procedures, and maintenance guidelines for various single-cylinder and twin-cylinder models.

Function Description

Great Power Engines are designed to power model aircraft, offering a range of horsepower outputs suitable for different aircraft sizes and performance requirements. These engines operate on a mixture of unleaded gasoline and synthetic oil, utilizing an ignition system to combust the fuel mixture and drive a propeller. The manual emphasizes safe operation and proper maintenance to ensure optimal performance and longevity.

Important Technical Specifications

The manual details specifications for several engine models, categorized into single-cylinder and twin-cylinder configurations.

Single-Cylinder Models:

GP38:
- Bore: 38 mm
- RPM Range: 1600-10000 RPM
- Net Weight: 1038 g
- Ignition Weight: 136 g
- Output: 5 Horsepower
- Fuel: Unleaded 89-93 Octane Fuel
- Lubrication: 40:1 Mixture of Octane Fuel and Synthetic Oil
- Pitts Muffler Weight: 144 g
- Recommended Propellers: Two-Blades (19x10, 20x8, 20x9), Three-Blade (18x10, 19x11 Narrow). Maximum power at 10000 RPM, do not exceed 9200 RPM during ground running.
- Propeller Bolts: M4x40 (65 in-lbs for Wood Prop, 70 in-lbs for Carbon Prop)
GP61:
- Bore: 46.5 mm
- RPM Range: 1600-8900 RPM
- Net Weight: 1507 g
- Ignition Weight: 136 g
- Output: 6.5 Horsepower
- Fuel: Unleaded 89-93 Octane Fuel
- Lubrication: 40:1 Mixture of Octane Fuel and Synthetic Oil
- Muffler Weight: 160 g
- Recommended Propellers: Two-Blades (22×12, 23×10, 24×8, 24×10), Three-Blade (21×12, 22×10). Maximum power at 8900 RPM, do not exceed 7700 RPM during ground running.
- Propeller Bolts: M5x45 (70 in-lbs for Wood Prop, 75 in-lbs for Carbon Prop)
GP88 V2:
- Bore: 53 mm
- RPM Range: 1200-8500 RPM
- Net Weight: 1980 g
- Ignition Weight: 136 g
- Output: 10 Horsepower
- Fuel: Unleaded 89-93 Octane Fuel
- Lubrication: 40:1 Mixture of Octane Fuel and Synthetic Oil
- Muffler Weight: 345 g
- Recommended Propellers: Two-Blades (26×10, 26×12, 27×10, 28×10). Maximum power at 8500 RPM, do not exceed 7300 RPM during ground running.
- Propeller Bolts: M5x45 (75 in-lbs for Wood Prop, 90 in-lbs for Carbon Prop)

Twin-Cylinder Models:

GP76:
- Bore: 38 mm
- RPM Range: 1400-9000 RPM
- Net Weight: 1720 g
- Ignition Weight: 202 g
- Output: 8 Horsepower
- Fuel: Unleaded 89-92 Octane Fuel
- Lubrication: 40:1 Mixture of Octane Fuel and Synthetic Oil
- Muffler Weight: 200 g
- Recommended Propellers: Two-Blades (22×12, 24×9, 24×10, 24×10TH, 25×8, 26×8), Three-Blades (21×12, 22×10, 22×12, 23×10). Maximum power at 9000 RPM, do not exceed 7700 RPM during ground running.
- Propeller Bolts: M5x45 (75 in-lbs for Wood Prop, 90 in-lbs for Carbon Prop)
GP123 V2:
- Bore: 46.5 mm
- RPM Range: 1500-8900 RPM
- Net Weight: 2300 g
- Ignition Weight: 202 g
- Output: 12 Horsepower
- Fuel: Unleaded 89-93 Octane Fuel
- Lubrication: 40:1 Mixture of Octane Fuel and Synthetic Oil
- Muffler Weight: 330 g
- Recommended Propellers: Two-Blades (27×12, 28×10, 28×12, 29×10), Three-Blades (25×12, 26×12). Maximum power at 8900 RPM, do not exceed 7300 RPM during ground running.
- Propeller Bolts: M5x50 (90 in-lbs for Wood Prop, 110 in-lbs for Carbon Prop)
GP178:
- Bore: 53 mm
- RPM Range: 1100-9000 RPM
- Net Weight: 3550 g
- Ignition Weight: 202 g
- Output: 21.5 Horsepower
- Fuel: Unleaded 89-92 Octane Fuel
- Lubrication: 40:1 Mixture of Octane Fuel and Synthetic Oil
- Muffler Weight: 430 g
- Recommended Propellers: Two-Blades (30×13, 31×12, 32×10). Maximum power at 9000 RPM, do not exceed 6700 RPM during ground running.
- Propeller Bolts: M6x55 (90 in-lbs for Wood Prop, 110 in-lbs for Carbon Prop). Special alloy (SNCM439) M6x55 screws are provided for GP178 due to high horsepower.

General Engine Specifications:

Fuel and Oil Mixture: Always use 40-50 units of unleaded 89-93 octane fuel mixed with 1 unit of synthetic oil (mixture ratio 40-50:1). Recommended oils are Red Line Two-Stroke Racing Oil and Motul 710. Do not use mixed fuel older than 90 days or synthetic oils intended for garden appliances.
Ignition System: Voltage Input: 6.6V~8.4V. Do not use the tachometer port for power.
Screw Torque Values:
- Spark Plug: 100 in-lbs (All Engines)
- Hub Screw: 250-280 in-lbs (All Engines)
- Crankcase Bolts: 90-100 in-lbs (M5x18 for GP38/GP88, M5x20 for GP61/GP76/GP178)
- Cylinder Base Bolts: 90 in-lbs (M5x16 for GP38/GP61/GP76/GP123), 90-100 in-lbs (M5x18 for GP88, M5x20 for GP178)
- Carburetor Mount Bolts: 70 in-lbs (M5x65 for GP38, M5x50 for GP61, M5x75 for GP76, M5x45 for GP88/GP123, M5x108 for GP178)

Usage Features

The manual provides comprehensive instructions for engine installation, propeller selection, end point adjustment, needle setting, and starting procedures.

Engine Installation:
- Mounting: Use M6 screws to mount the engine on a stiff firewall. High-grade 1/4 bolts with washers and locknuts are recommended.
- Servo: A high-quality servo and linkage are recommended for throttle control. Avoid metallic servo linkages to prevent radio interference.
- Fuel Tank: Recommended tank sizes vary by engine model (450-500cc for GP61, 600-800cc for GP76, 800-1000cc for GP123/GP88, 1500cc for GP178). The tank must be vented to the outside, preferably at the bottom of the cowl.
- Cooling: Proper air circulation is critical. The exhaust outlet should be 3 times larger than the intake. Baffles are recommended to direct airflow over cylinder fins for maximum cooling.
- Caution: Use seals to prevent debris from entering the engine interior during mounting.
Choosing a Propeller:
- Propeller performance varies by manufacturer and material (carbon fiber typically yields higher RPM than wood).
- Balance: Always balance the propeller to prevent vibration, bearing damage, and crankshaft twist.
- Drilling: Use a drill press for precise drilling of propeller bolts. Imprecise drilling can lead to sheared bolts.
- Back Plate: Avoid using carbon fiber back plates with spinners; alloy back plates are recommended.
End Point Adjustment: Instructions are provided for adjusting servo and carburetor linkages to ensure proper throttle range (L1=L2 and x°=y°).
Needle Setting:
- Needles are factory pre-adjusted. Turning clockwise leans the mixture, counter-clockwise richens it.
- Starting Points: Specific low and high needle settings are provided for each engine model (e.g., GP38: Low 1 3/4 open, High 1 1/2 open).
- Caution: Do not overtighten needles to avoid damage.
- Symptoms of Running Lean: Engine stalling on acceleration, slowing at full throttle, overheating, difficulty starting, rough idling, backfiring, lurching acceleration, white/light gray spark plugs/muffler end pipes, requiring excessive choke.
- Symptoms of Running Rich: Sluggish performance, excessive smoke, engine stalling on acceleration, easy overflowing at start, slow throttle response, poor fuel economy, choke not needed from cold starts, sooty/black spark plugs/muffler end pipes, strong gasoline smell at idle, uneven running.
Starting Procedure:
- Ensure propeller bolts are tightened and the area is clear of debris.
- Two people are required: one to hold the plane (with eye protection), one to start the engine (wearing heavy-duty leather gloves).
- Switch on the radio system and verify controls. Set throttle cut to fully close the throttle.
- Switch on ignition, close the choke, and flip the propeller until the engine starts briefly.
- Release the choke, set throttle slightly above idle, and flip the propeller to start. It usually takes 5-10 flips. Be aware the engine can start on any flip, even with ignition off.
- After starting, slowly push throttle to low idle for 30 seconds to warm up. Slowly open to full throttle for 5 seconds to check maximum power, then return to low idle.
Break-In:
- Break in the engine on a plane, not a test stand, to prevent overheating.
- The engine is fully broken-in after 25 liters of fuel.
- Procedure:
  1. Idle for 2-3 minutes (below 2500 RPM).
  2. Run at 4000-4500 RPM for one tank of fuel, then shut off and cool.
  3. Restart at idle for 1 minute, then slowly push to full throttle (not exceeding 5 seconds). Ensure correct needle settings.
  4. Shut off and cool before flying.
- Caution: Ensure a proper cooling system before flying. Do not operate at full throttle for over 10 seconds before break-in is complete.
Troubleshooting (Engine Won't Start):
- Check battery voltage (over 6.6V under load).
- Verify ignition connections, wiring, and switches.
- Inspect fuel system for clogs, jams, or bad lines.
- Ensure propeller is flipped with authority.
- Check for tight carburetor mount to prevent air leaks.
- If overflowed: turn off ignition, open choke and throttle, flip propeller 10 times at full throttle, then close throttle to idle and restart. For single-cylinder engines, check/dry/replace spark plugs.
- If engine starts and stops immediately, low needle is likely too lean (turn counter-clockwise 1/8 turn).
- If engine doesn't reach normal RPM at full throttle: revert to GP mufflers and original needle settings. Potential causes include low battery, oversized propeller, incorrect fuel/oil mixture, muffler/pipe system issues, incorrect ignition timing, or failing spark plugs.
- If engine runs roughly or vibrates strongly: check if low needle is too rich, propeller/spinner balance, engine mount bolts, ignition timing, and engine box/firewall structure.

Maintenance Features

The manual outlines regular maintenance checks and a limited warranty policy.

Regular Checks:
- Regularly check for fuel seepage, which can indicate a lean fuel/air ratio and cause erratic running or damage.
- Spark plug replacement is recommended every 20 hours of running.
- Reed valve check is recommended after 50 hours.
- A complete engine checkup by authorized service centers is recommended after 300 hours.
- For GP178, certain parts (pistons, piston rings, needle bearings, spark plugs) may wear out more quickly and require occasional replacement to maintain peak performance.
- Regularly check and tighten all engine, firewall, and propeller screws to their specified torque values.
Limited Warranty:
- Duration: TWO (2) YEARS from the date of original purchase from authorized dealers.
- Validity: Requires the GP-issued Warranty Card with Date of Purchase and dealer's/seller's name, or proof of purchase. If not available, the Manufacture Date recorded by GP will be used.
- Transferability: Only the original owner is eligible.
- Coverage: Covers parts of GP engines and ignitions (CDI).
- Exclusions: Does NOT cover mufflers (given free). Does NOT cover damage from misuse, mishandling, unskilled repair, unauthorized modification/disassembly, crash/crush, use of aftermarket parts, or low-quality/improper fuel/additives.
- Includes: Repair and replacement of defective parts/engines, shipping charges, and labor charges.
- Claim Process: Requires Warranty Card, Maintenance Form (from www.gpengine.world/news/11), and photos/videos of issues.
- GP has absolute discretion to approve or reject claims.