ATHENA Big Bore 304 Cylinder Kit Ø85 mm for YAMAHA YZF 250 2021-2023

On YAMAHA YZF 250 from 2021 to 2023, the ATHENA Big Bore 304 Ø85 mm P400485100105 cylinder kit fits in place of the original part. 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: P400485100105
• EAN code: 8056216244273
• Weight: 1.44 kg
• Engine: 4-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
• Piston rings : ATHENA
• Top end gasket kit : ATHENA
• Spark plug : see the selection
• Coolant : LIQUI MOLY 1 L · TWIN AIR

Frequently asked questions

What does the kit contain?
The cylinder and its complete piston. Check the photo and the Athena instructions for the gaskets supplied.

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 YZF 250 2023
YAMAHA YZF 250 2022
YAMAHA YZF 250 2021