PROX Countershaft Seal Kit for YAMAHA YZ 250 and FANTIC XX 250 1999-2026

On YAMAHA YZ 250 and FANTIC XX 250 from 1999 to 2026, the PROX 26.640021 countershaft seal kit fits in place of the original part. An oil leak behind the countershaft sprocket almost always comes from the oil seal and its bush. This kit brings together the parts to replace at the same time.

Specifications

• Brand: PROX
• Manufacturer part number: 26.640021
• Weight: 70 g
• Engine: 2-stroke

When to replace it?

• Oil on the countershaft sprocket and the crankcase.
• Gearbox oil level dropping.
• Bush scored or marked where the lip runs.

As soon as a leak appears behind the sprocket, and when changing the chain and sprockets if the bush is marked.

Fitting tips

1. Remove the countershaft sprocket, then the bush and the seal, without scratching the housing.
2. Oil the O-ring and the lip of the new seal.
3. Press the seal in perfectly square, then fit the new bush.
4. Top up the gearbox oil.

Why PROX?

ProX Racing Parts has been supplying engine and clutch parts to motocross riders since 1975, from its headquarters near Amsterdam. According to its catalogue, most of its parts are made in Japan, by manufacturers that also produce parts for the Japanese motorcycle makers.

Spare parts and items to plan

• Gearbox oil : LIQUI MOLY 10W30 1 L · LIQUI MOLY 1 L

Frequently asked questions

What does the kit contain?
Depending on the model: oil seal, bush and O-ring. If in doubt, compare with your original parts.

Compatibility

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

Fits:
FANTIC XX 250 2026
FANTIC XX 250 2025
FANTIC XX 250 2024
FANTIC XX 250 2023
FANTIC XX 250 2022
YAMAHA YZ 250 2026
YAMAHA YZ 250 2025
YAMAHA YZ 250 2024
YAMAHA YZ 250 2023
YAMAHA YZ 250 2022
YAMAHA YZ 250 2021
YAMAHA YZ 250 2020
YAMAHA YZ 250 2019
YAMAHA YZ 250 2018
YAMAHA YZ 250 2017
YAMAHA YZ 250 2016
YAMAHA YZ 250 2015
YAMAHA YZ 250 2014
YAMAHA YZ 250 2013
YAMAHA YZ 250 2012
YAMAHA YZ 250 2011
YAMAHA YZ 250 2010
YAMAHA YZ 250 2009
YAMAHA YZ 250 2008
YAMAHA YZ 250 2007
YAMAHA YZ 250 2006
YAMAHA YZ 250 2005
YAMAHA YZ 250 2004
YAMAHA YZ 250 2003
YAMAHA YZ 250 2002
YAMAHA YZ 250 2001
YAMAHA YZ 250 2000
YAMAHA YZ 250 1999