ATHENA Big Bore 144 Cylinder Kit Ø58 mm for YAMAHA YZ 125 2022-2026

The ATHENA Big Bore 144 Ø58 mm P400485100101 cylinder kit is designed for YAMAHA YZ 125 from 2022 to 2026. A cylinder that is scored, oval or has a damaged coating loses compression and wears pistons out quickly. Rather than having it rebored and recoated, this kit replaces it with a new, ready-to-fit cylinder.

Specifications

• Brand: ATHENA
• Manufacturer part number: P400485100101
• EAN code: 8050506053798
• Weight: 2.56 kg
• Engine: 2-stroke

When to replace it?

• Cylinder scored or coating flaking after a seizure.
• Ovality or taper out of tolerance when measured with a micrometer.
• You want more torque and power without touching the bottom end.

Measure the cylinder at every piston change. As soon as it falls outside the tolerances in the manual or is scored, it has to be replaced or reconditioned.

Fitting tips

1. Carefully clean the top of the crankcase and cover its opening before removing the old cylinder.
2. Oil the supplied piston and check the ring end gaps before fitting the cylinder.
3. Use new gaskets, either those in the kit or a suitable top end gasket kit, and tighten the cylinder and head in a criss-cross pattern to the manufacturer's torque.
4. Fit a new spark plug and refill the coolant.
5. Break the engine in gently for 3 to 4 hours, as Athena recommends for its cylinder kits.

Why ATHENA?

Founded in 1973 near Vicenza, Athena is an Italian engine gasket specialist that has made its gaskets on its own production lines since day one, as well as a renowned manufacturer of pistons and cylinder kits. The brand supplies original equipment to manufacturers such as KTM, Ducati, Fantic, Piaggio and Triumph, and is a partner of the MXGP motocross world championship.

Spare parts and items to plan

• Piston : ATHENA
• Top end gasket kit : ATHENA
• Cylinder head and dome : ATHENA S410485308040 · ATHENA P400485200003
• Exhaust power valve parts : ATHENA
• Cylinder kit bolt kit : ATHENA
• Spark plug : NGK 3530 · NGK 3230
• Coolant : LIQUI MOLY 1 L · TWIN AIR

Frequently asked questions

What does the kit contain?
The cylinder, its complete piston and a specific gasket kit.

Is it road legal?
No: a Big Bore kit increases displacement; it is for closed-course competition only and may change your racing class.

Which spare parts should I plan for?
For the next service: piston, rings, pin, circlips and top end gaskets in the same size as this cylinder.

Compatibility

Check the exact model and year of your bike in the list below before ordering.

Fits:
YAMAHA YZ 125 2026
YAMAHA YZ 125 2025
YAMAHA YZ 125 2024
YAMAHA YZ 125 2023
YAMAHA YZ 125 2022