ATHENA Racing Forged Piston for GAS GAS CONTACT 250, EC 250, ECF 250, MC 250, PAMPERA 250 1999-2014

The ATHENA Racing forged piston (Ø 66.33 to 66.36 mm depending on the size class) is designed for GAS GAS CONTACT 250, EC 250, ECF 250, MC 250, PAMPERA 250 from 1999 to 2014. A forged piston is made by squeezing a hot aluminium slug in a press, instead of pouring the metal into a mould. The metal is denser and stronger: the piston copes better with high revs and heat, which makes it the choice for racing engines.

Key features

• High-silicon aluminium alloy, forged by reverse extrusion.
• CNC machined to a tolerance of less than 0.01 mm, tested on the bench and on the track.
• Rings made in Japan, with a PVD or chromium nitride coating.
• Supplied with pin, circlips and ring(s).

Specifications

• Brand: ATHENA
• Manufacturer part numbers: S4F06640014A, S4F06640014B, S4F06640014C, S4F06640014D
• Engine: 2-stroke
• Piston diameter: A = 66.33 mm, B = 66.34 mm, C = 66.35 mm, D = 66.36 mm
• Available versions: A: ref. S4F06640014A; B: ref. S4F06640014B; C: ref. S4F06640014C; D: ref. S4F06640014D
• Weight: 390 g

Choosing the right size class

The letters A, B, C… are very close diameter grades, one hundredth of a millimetre apart. Measure the cylinder bore with a bore gauge (diameter, ovality and taper) and choose the grade that gives the piston-to-cylinder clearance specified by the manufacturer. As a rule, grade A goes into a new or reconditioned cylinder, grade B into a cylinder that has already been run in. A scored or out-of-spec cylinder has to be reconditioned: you don't make up for its wear with a bigger grade.

When to replace it?

• Loss of power, sluggish pick-up, harder starting: compression is dropping.
• Piston slap on a cold engine, getting more and more noticeable.
• On teardown: vertical scoring on the skirt, stuck or worn rings, thick carbon on the crown.

Replace the piston as set out in your bike's service manual, sooner if you race, and straight away as soon as these symptoms appear. As a Cross-Mania guideline, plan for a new piston every 20 to 40 hours of engine running depending on whether you race or ride for fun. Always measure the cylinder at the same time: a new piston in an oval cylinder won't last.

Fitting tips

1. Clean the cylinder and check it: diameter, ovality, taper and condition of the bore coating.
2. Check the end gap of each ring in the cylinder against the figures in the manual or the manufacturer's instructions.
3. Fit the rings with the mark facing up and each gap correctly located on its locating pin.
4. Fit the piston with its arrow pointing to the exhaust side, oil the pin and the small end, then fit the circlips without distorting them, gap opposite the notch. A circlip that has been taken out is replaced with new piston pin circlips, never refitted.
5. Reassemble with a new top end gasket kit and tighten the cylinder head in a criss-cross pattern to the manufacturer's torque.
6. Break the engine in: warm it up gently, vary the revs and avoid sustained full throttle for the first hour.

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 rings : WISECO · PROX
• Piston pin : WOSSNER CW18 · WOSSNER WP033
• Piston pin clips : WISECO · VERTEX
• Top-end gasket kit : TECNIUM · ATHENA
• Small end needle bearing : PROX · NTN
• Spark plug : NGK 6637 · NGK 3430
• Coolant : LIQUI MOLY 1 L · TWIN AIR
• 2-stroke oil : LIQUI MOLY 1 L · LIQUI MOLY 4 L

Frequently asked questions

Does the piston come complete?
Yes: piston, pin, circlips and ring(s). The top end gasket kit has to be ordered separately, because a head or base gasket can never be reused.

Which size should I order?
Measure your cylinder: A, B, C, D correspond to different actual diameters (66.33 to 66.36 mm). Choose the class that gives the piston-to-cylinder clearance specified by the manufacturer.

Can I replace just the rings later?
Yes, as long as the piston and cylinder are still within tolerance. Replacement rings can be ordered on their own, as can the piston pin and the circlips.

Compatibility

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

Fits:
GAS GAS CONTACT 250 2004
GAS GAS CONTACT 250 2003
GAS GAS CONTACT 250 2002
GAS GAS CONTACT 250 2001
GAS GAS CONTACT 250 2000
GAS GAS CONTACT 250 1999
GAS GAS EC 250 2014
GAS GAS EC 250 2013
GAS GAS EC 250 2012
GAS GAS EC 250 2011
GAS GAS EC 250 2010
GAS GAS EC 250 2009
GAS GAS EC 250 2008
GAS GAS EC 250 2007
GAS GAS EC 250 2006
GAS GAS EC 250 2005
GAS GAS EC 250 2004
GAS GAS EC 250 2003
GAS GAS EC 250 2002
GAS GAS EC 250 2001
GAS GAS EC 250 2000
GAS GAS EC 250 1999
GAS GAS ECF 250 2005
GAS GAS ECF 250 2004
GAS GAS ECF 250 2003
GAS GAS ECF 250 2002
GAS GAS ECF 250 2001
GAS GAS ECF 250 2000
GAS GAS ECF 250 1999
GAS GAS MC 250 2009
GAS GAS MC 250 2008
GAS GAS MC 250 2007
GAS GAS MC 250 2006
GAS GAS MC 250 2005
GAS GAS MC 250 2004
GAS GAS MC 250 2003
GAS GAS PAMPERA 250 2004
GAS GAS PAMPERA 250 2003
GAS GAS PAMPERA 250 2002
GAS GAS PAMPERA 250 2001
GAS GAS PAMPERA 250 2000
GAS GAS PAMPERA 250 1999