just had a look through my bike manual and noticed that the chain slack reads 40.0 -55.0mm (1.57-2.17 inch)

My last bike only needed approx 35mm slack.......

Any thoughts please i have trawled through the forum but not founf a definitive answer for the xt660x i'm a little concenred not to tighten it to what i'm used to due to the extra wear and tare etc...

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2004-2006 Yamaha R603 plate Akra carbon can Ohlins steering damper carbon air intakes/rear fender/hugger double bubble race screen YM600 cycle lock LED indicators tail tidy
2009 - 2009 Yamaha R657 plate with titanium Akra full exhaust system ASV short levers Carbon fuel tank/front fender/rear hugger Ohlins steering damper LED indicators, double bubble race screen
2011 - now Yamaha XT660X 56 plate mtc cans 2b contd...