ATHENA Top End Gasket Kit for KTM GS 125, MX 125 1984-1986

The ATHENA P400270600012 top end gasket kit is designed for KTM GS 125, MX 125 from 1984 to 1986. The top end gasket kit brings together the gaskets to replace every time the cylinder head or cylinder comes off. A gasket crushed by tightening never gets its shape back: refitting it means risking a compression, coolant or oil leak, and having to strip everything down again.

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: P400270600012
• EAN code: 8055681302587
• 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?

Athena, an Italian company founded in 1973 near Vicenza, designs gaskets, pistons and cylinder kits for motorcycles. An OEM supplier to KTM, Ducati, Fantic, Piaggio and Triumph and a partner of the MXGP world championship, it develops its parts on the test bench and on the track with racing teams.

Spare parts and items to plan

• Piston : VERTEX · WOSSNER
• Piston rings : VERTEX · WOSSNER
• Spark plug : see the selection
• Coolant : LIQUI MOLY 1 L · TWIN AIR
• 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:
KTM GS 125 1986
KTM GS 125 1985
KTM GS 125 1984
KTM MX 125 1986
KTM MX 125 1985
KTM MX 125 1984