ATHENA Racing Forged Piston for YAMAHA WR 125, YZ 125 2005-2021

ATHENA offers this piston kit for YAMAHA WR 125, YZ 125 2005-2021. The piston slides in the cylinder and takes the force of the air-fuel combustion, passing it to the connecting rod and crankshaft.

Why choose a forged piston?

Instead of simply being cast, a forged piston is hot-pressed under very high pressure and then machined: its metal is denser and free of air pockets.

• Stronger when hot: it copes better with high revs, overheating and detonation.
• Lighter for the same strength: less stress on the connecting rod and bearings.
• Good to know: depending on the alloy, it expands a little more and is fitted with more clearance; slight noise when cold is normal.
• Why does it cost more? Forging tools, full machining and surface treatments cost more than simple casting.

Why choose ATHENA?

Athena, the Italian manufacturer founded in 1973, is an original-equipment supplier to manufacturers such as KTM and Ducati: the same standards for your replacement parts.

When should you replace the piston on your YAMAHA YZ 125?

Harder starting, loss of power, blue smoke, oil consumption or a knock when cold: these are the signs of a tired top end.

No manufacturer hour figure for this model. Cross-Mania guideline: compression check every 20 h in hard use and every 40 h for leisure.

Specifications and fitting tips

• Engine: 2-stroke
• Manufacturer part numbers: S4F05400017A (A), S4F05400017C (C)

Available in several sizes: choose the one that matches your cylinder (stamped size or measured bore). Diameters: A = 53.95 mm, C = 53.97 mm.

Spare parts and items to plan

• Piston rings : PROX · VERTEX
• Piston pin : VERTEX · WOSSNER
• Piston pin clips : WOSSNER
• Top-end gasket kit : ATHENA · ATHENA 150
• Small end needle bearing : HOT RODS · ATHENA
• Spark plug : NGK 3530 · NGK 3230
• Coolant : LIQUI MOLY 1 L · TWIN AIR
• 2-stroke oil : LIQUI MOLY 1 L · LIQUI MOLY 4 L

Compatibility

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

Fits:
YAMAHA WR 125 2018
YAMAHA WR 125 2017
YAMAHA WR 125 2016
YAMAHA WR 125 2015
YAMAHA WR 125 2014
YAMAHA WR 125 2013
YAMAHA WR 125 2012
YAMAHA WR 125 2011
YAMAHA WR 125 2010
YAMAHA WR 125 2009
YAMAHA WR 125 2008
YAMAHA WR 125 2007
YAMAHA WR 125 2006
YAMAHA WR 125 2005
YAMAHA YZ 125 2021
YAMAHA YZ 125 2020
YAMAHA YZ 125 2019
YAMAHA YZ 125 2018
YAMAHA YZ 125 2017
YAMAHA YZ 125 2016
YAMAHA YZ 125 2015
YAMAHA YZ 125 2014
YAMAHA YZ 125 2013
YAMAHA YZ 125 2012
YAMAHA YZ 125 2011
YAMAHA YZ 125 2010
YAMAHA YZ 125 2009
YAMAHA YZ 125 2008
YAMAHA YZ 125 2007
YAMAHA YZ 125 2006
YAMAHA YZ 125 2005