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Buy a service manual
http://safemanuals.com/user-guide-instructions-owner-manual/YAMAHA/PW80-2003-_E
Clymer manual Clymer manual
You can view the 2003 Ford Explorer owners manual online at : www . motorcraft service . com ( no spaces ) Click on Owner Guides
Dealer
Lance's Haynes manual says: Capacity: 555cc, Type: Yamaha fork oil "01" or equivalent
You can download the manual at: http://www.motorcraftservice.com/pubs/content/~WO3F12/~MUS~LEN/36/03f12og5e.pdf
Ebay
They are listed in the manual. If you do not have a manual then you can download a PDF from our enthusiasts forum at www.trailvoy.com
i found mine on google it was a pdf file.
replacing 2003 fore explorer sport front wheel bearings
Buy a service manual and read it.