WÖSSNER Piston Kit for YAMAHA WRF 450, YZF 450 and GAS GAS ECF 450 2003-2015

On YAMAHA WRF 450, YZF 450 and GAS GAS ECF 450 from 2003 to 2015, the WÖSSNER 8631DC piston kit (Ø 94.98 mm) fits in place of the original part. At the heart of the top end, the piston soaks up the heat and pressure of every explosion. As it wears, the rings no longer seal against the cylinder: compression drops, power drops with it, and the risk of seizure goes up.

Key features

• Forged piston in T6 heat-treated 4032 alloy, designed using computer simulation (FEA).
• Permanent skirt coating that reduces friction.
• Very tight running clearance, for a quieter engine (according to Wössner).
• Complete kit: piston, rings, pin and circlips. Small-end needle bearing not included.

Specifications

• Brand: WÖSSNER
• Manufacturer part number: 8631DC
• Size: C (check that it matches your cylinder)
• Piston diameter: 94.98 mm
• Engine: 4-stroke

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 30 to 60 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. Refill the coolant, 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 WÖSSNER?

Wössner is a German family business based in Weil am Rhein and founded by Eckart Wössner, a former racer from the 1970s. It has been making its own forged pistons since 1994, from blanks produced in its own forge, and Wössner pistons are used in Supercross as well as in MXGP.

Spare parts and items to plan

• Piston rings : VERTEX · ATHENA
• Piston pin : WOSSNER CW20 · WOSSNER CW19
• Piston pin clips : WISECO
• Top-end gasket kit : see the selection
• Spark plug : NGK 4218 · NGK 3521
• Coolant : LIQUI MOLY 1 L · TWIN AIR
• 4-stroke engine oil : LIQUI MOLY 10W40 1 L · MOTUL 10W50

Frequently asked questions

Does the kit include the gaskets?
No: the kit contains the piston, rings, pin and circlips. Add a top end gasket kit, 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:
GAS GAS ECF 450 2014
GAS GAS ECF 450 2013
YAMAHA WRF 450 2015
YAMAHA WRF 450 2014
YAMAHA WRF 450 2013
YAMAHA WRF 450 2012
YAMAHA WRF 450 2011
YAMAHA WRF 450 2010
YAMAHA WRF 450 2009
YAMAHA WRF 450 2008
YAMAHA WRF 450 2007
YAMAHA WRF 450 2006
YAMAHA WRF 450 2005
YAMAHA WRF 450 2004
YAMAHA WRF 450 2003
YAMAHA YZF 450 2009
YAMAHA YZF 450 2008
YAMAHA YZF 450 2007
YAMAHA YZF 450 2006
YAMAHA YZF 450 2005
YAMAHA YZF 450 2004
YAMAHA YZF 450 2003