ATHENA Racing Forged Piston ref. S4F087000010 for YAMAHA TT 350 1985-1996

The ATHENA Racing S4F087000010 forged piston (Ø 86.94 mm) is designed for YAMAHA TT 350 from 1985 to 1996. 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 number: S4F087000010
• EAN code: 8050444894453
• Engine: 4-stroke
• Piston diameter: 86.94 mm
• Weight: 490 g

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.
• On a four-stroke: oil consumption, blue smoke and a fouled spark plug.

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 50 to 100 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 the gaps staggered, never letting the ends of the oil control ring overlap.
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. Fit a new spark plug and change the oil, with fresh engine oil and a new filter.
7. 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 : see the selection
• Piston pin : WOSSNER
• Top-end gasket kit : CENTAURO
• Spark plug : NGK 2120 · NGK 6681
• 4-stroke engine oil : LIQUI MOLY 10W40 1 L · MOTUL 10W50

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.

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:
YAMAHA TT 350 1996
YAMAHA TT 350 1995
YAMAHA TT 350 1994
YAMAHA TT 350 1993
YAMAHA TT 350 1992
YAMAHA TT 350 1991
YAMAHA TT 350 1990
YAMAHA TT 350 1989
YAMAHA TT 350 1988
YAMAHA TT 350 1987
YAMAHA TT 350 1986
YAMAHA TT 350 1985