ATHENA Top End Gasket Kit for ATHENA Big Bore cylinder kit for TM RACING EN 250, MX 250 2019-2026

The ATHENA P400465600011 top end gasket kit is designed for TM RACING EN 250, MX 250 from 2019 to 2026. As soon as the cylinder head or cylinder is removed, their gaskets must be replaced: crushed when tightened, they have taken the shape of the parts and will no longer seal. This kit groups under one part number the gaskets needed to reassemble the top end.

Key features

• Head, base and exhaust gaskets, O-rings and washers, depending on the model.
• Laser cutting and surface treatments for consistent sealing.
• Designed by Athena, an OEM supplier, and validated on test benches.

Specifications

• Brand: ATHENA
• Manufacturer part number: P400465600011
• EAN code: 8056216246413
• Weight: 60 g
• Engine: 2-stroke

When to replace it?

• Coolant or oil seeping at the head/cylinder or cylinder/crankcase joint.
• Coolant level dropping, bubbles in the radiator.
• Hissing or black marks where the exhaust leaves the cylinder.

At every piston change and every time the cylinder head or cylinder is removed, even for a simple inspection. Gaskets cost little compared with the work of stripping the engine.

Fitting tips

1. Clean the gasket faces without scratching them (plastic scraper, solvent): they must be clean, dry and free of burrs.
2. Fit the gaskets dry, without sealant, unless the workshop manual says otherwise.
3. Refit a base gasket of the same thickness as the old one, unless you are deliberately adjusting the squish.
4. Tighten the cylinder head in a criss-cross pattern, in several stages, up to the manufacturer's torque.
5. While it's apart, replace the spark plug and refill the coolant.
6. After break-in, check the torque with the engine cold and make sure there are no leaks.

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

• Coolant : TWIN AIR 1 L · MOTUL 1 L
• 2-stroke oil : LIQUI MOLY 1 L · MOTUL 1 L

Frequently asked questions

What does the kit contain?
Depending on the model: head gasket, base gasket, exhaust gasket, O-rings and washers. Compare with your original gaskets if you're unsure.

Should I replace it along with the piston?
Yes: as soon as the cylinder head and cylinder are off, new gaskets go back on. It's the right time to fit a new piston kit and new rings if the engine has some hours on it.

Compatibility

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

Fits:
TM RACING EN 250 2026
TM RACING EN 250 2025
TM RACING EN 250 2024
TM RACING EN 250 2023
TM RACING EN 250 2022
TM RACING EN 250 2021
TM RACING EN 250 2020
TM RACING EN 250 2019
TM RACING MX 250 2026
TM RACING MX 250 2025
TM RACING MX 250 2024
TM RACING MX 250 2023
TM RACING MX 250 2022
TM RACING MX 250 2021
TM RACING MX 250 2020
TM RACING MX 250 2019