Just an interesting piece of info... My 98 WR400 engine has been jumping time on me recently. It appears as if the cam chain has stretched. While studying my problem I noticed the stock cam chain tensioner. I have always thought about putting a manual cam chain tensioner on the bike (as on my fzr1000 vintage racer)to replace the stock one. Not sure how the stock ones hold up on the 400's, but the design on the yamaha 750/1000 street motors was lacking. It was possible for the automatic tensioner to momentarily retract (it would jump past the ratchet mechanism) and possibly allow timing to jump. Hence most hopped up 750/1000 engines went with the manual cam chain tensioners. Guess what... the manual cam chain tensioner from those bikes fits the wr400 (and 426 I would assume) without any modification whatsoever, same gasket and all. I know the manual tensioner is higher maintenance, but it always gave me piece of mind knowing it couldnt back off momentarily. The one I used is made by APE. Any year FZR1000 will work.