Selecting the right motorcycle spark plug requires comprehensive consideration of factors such as vehicle compatibility, thermal value, electrode material, thread specifications, and usage scenarios.
| Parameters | Description | Common Options/Examples |
| Heat Value | Spark Plug Heat Dissipation | Cool Type (High Values such as 8/9/10), Hot Type (Low Values such as 5/6/7) |
| Thread Diameter | Spark Plug Mounting Hole Size | 12mm (Compact Car), 14mm (Mainstream), 18mm (Heavy Motorcycle) |
| Thread Length | Thread Length into Cylinder | Short Thread (12.5mm), Long Thread (19mm) |
| Electrode Material | Durability and Ignition Efficiency | Nickel Alloy (Basic), Platinum (Long-Lasting), Iridium (High-Performance) |
| Electrode Gap | Spark Jump Distance (mm) | 0.6-1.0mm (Must strictly match manual specifications) |
(1) Check the original manufacturer's manual (most important!)
Look through the vehicle's user manual or repair manual to find the manufacturer's specified spark plug model.
Do not replace it at will: the original manufacturer's model matches the engine's compression ratio, ignition system, and fuel type.
(2) Determine the calorific value (heat dissipation capacity)
| Heat Value Type | Applicable Scenarios | Example Values (NGK Standard) |
| Cold Type | High RPM/High Compression Ratio/Long Distance Ride | 8, 9, 10 (Higher Values, Colder) |
| Hot Type | Low RPM/Low Compression Ratio/Short Distance Ride | 5, 6, 7 (Lower Values, Hotter) |
Consequences of an incorrect heat value:
Cold models (overcooling) → Increased carbon deposits and unstable idling.
Hot models (overheating) → Pre-ignition and electrode meltdown.
(1) Excessive Electrode Wear:
The center electrode is burned and rounded or the tip is concave > 0.5mm (compared to a new plug).
The depth of the side electrode notch is > 0.3mm (measured with a feeler gauge).
Consequences: Spark dispersion and reduced ignition energy.
(2) Insulator Crack:
Ceramic insulator cracks or breaks.
Consequences: High voltage leakage, resulting in fire and power drop.
(3) Electrode Meltdown:
The tip of the electrode is locally melted to form a tumor or fracture (mostly caused by overheating).
Consequences: Metal debris may fall into the cylinder and scratch the cylinder wall.
(4) Severe Carbon Deposits/Oil Contamination:
The electrode is completely covered by a black carbon layer (too rich mixture) or soaked in engine oil (burning oil). It cannot be restored after cleaning.
After removing the spark plug, refer to this table for a quick judgment:
| Status | Characteristics | Problem Reported | Solution |
| Healthy Status | Electrode is gray-brown, ceramic substrate is white | Good combustion | Reusable after cleaning |
| Excessive carbon deposits | Electrode covered with black, dry carbon powder | Too rich mixture/long-term low speed operation | Clean or replace |
| Viscous oil stains | Wet electrode with oil stains | Oil burning/cylinder seal failure | Replace and overhaul engine |
| Whitening due to overheating | Electrode is gray-white, insulator has molten spots | Low calorific value (too hot) | Replace with a cooler spark plug |
| Lead contamination | Yellow-green enamel on electrode surface | Using leaded gasoline | Switch to unleaded gasoline |
NINGBO MARSHAL AUTO PARTS CO., LTD. is a research and development, production and sales of professional manufacturers of spark plugs. Our company's spark plugs are mainly used in gasoline, natural gas and liquefied petroleum gas as fuel for all types of automobiles.
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