Forged Piston YZ 125 size B

Piston Athena Yamaha 125 YZ

When to replace the piston?

Motocross pistons must be replaced regularly. You will find more detailed information on the maintenance intervals in your motorcycle's user manual.

In general, the piston must be replaced depending on the use (motocross, enduro, sand only, etc.), rider level (a beginner uses the engine differently than a pro rider) and displacement (the more RPM the engine can make, the more often the piston must be replaced: In motocross, for example, the piston of a 125cc is replaced more frequently than that of a 250cc with the same rider and use).

Note: it is best to order a cylinder gasket set at the same time.

How do I choose my piston?

The choice of the right piston depends largely on the cylinder. Although the cylinder generally wears out more slowly, it also wears out. The combination of piston and cylinder must therefore always be perfectly matched. With the right tools, you can measure the cylinder and compare it with the original dimensions:

• New motorcycle:
  • Cylinder bore = 54 mm
  • Piston in standard dimension (dimension A) = 53.95 mm
  • Piston clearance: 54 - 53.95 = 0.05 mm
• After several hours of operation:
  • Measured cylinder bore = 54.01 mm
  • Piston size = 54.01 - 0.05 = 53.96 mm
  • Select size B to maintain the right clearance

Our tip: especially if you have no special knowledge of engine tuning, you should always choose the same piston type as the original and just make sure you choose the correct size.

Technical data Athena piston Yamaha YZ 125:

• Two-stroke piston made from silicon 4032
• Four-stroke piston made from silicon 2618 (the same material used for Formula 1 pistons)
• Contains 3% copper for better heat resistance
• All pistons are forged using a precise heat treatment process that allows manufacturing tolerances of just 0.005 mm
• The machining of the forged pistons ensures a low weight
• Kits include the piston, rings, piston pin and retaining clips