ok so i thought i would share my personal fix and problem with my 09 xt660x as there is very little info on the net about this exact problem. the way it happened for me ....... ok so i bought my baby with 10500 miles on it a few months back and i took it for a long hard ride and came back with a knock under acceleration
i instantly thought the worst thinking i had killed the big end bearings as that was wear the sound seemed to be coming from. so i rode it for a few days to check it wasn't my imagination and there was still a knock there that was bothering me so i took it to 3 different local bike mechanics they all agreed it sounded "corse" but said its "just a big single and that's all the noise is keep riding it and see if it gets worse" so my mechanic instincts kicked in (car mechanic) and i new something was wrong as the sound had changed and sounded very metallic when accelerating / decelerating the engine from a fixed speed . i also realized that if i put it in gear and hold the front brake and try and drive (take up any slack in transmission ) it would sound just like hitting a hammer on the top of a vice. which cant be good so i did some research and found very little info on it so i decided i would strip the oil filter, water pump, clutch cover and arm, and the right hand side foot peg off so i could take the crank cover off. when i looked close i could see that the primary gears on the end of the crank shaft could be rotated a fair way either way before the shaft stopped it from rotating freely so i un folded the lock tab which had no signs of allowing the nut to spin and found once this was out the way i could rotate the nut off the end of the shaft by hand .... obviously this wasn't right so i tried some more research and found something to do with on the newer models the torque settings had been reduced even tho its the same components they just deiced to fit the newer engines with a lower torque measurement . so i found some were on the web which stated the older torque measurement was 110nm so i went and bought a new lock tab washer and some permanent lock tight and resembled the nut back onto the crankshaft (luckily they was no signs of wear or damage)

so with the lock tight and new tab washer i torques it up to 110nm which was rather tricky because of having to take up the transmission slack while on a paddock stand but i managed it in the end then i bent the tab washer over one of the flat sides of the washer and also manged to bend the other side of the washer into a triangle over the top corner of the nut i then rebuilt the bike put it all back together and have done 1300 hard miles since and there's still no knock all this cost me about 4 hours of my time laid infront of a heater and about �10 for the new washed and loctite .

just thought i would share my story as i think it might be pretty helpfull for others cos when it first started i was prety worried thinking that sounds expensive lol
below you will see three youtube links of the knock and also of the fix

any questions just message me or comment below.ash
happy riding

vid 1 of knock http://www.youtube.com/watch?v=1yOV3...ature=youtu.be

vid 2 of more knocking noise http://www.youtube.com/watch?v=bEggx...ature=youtu.be

vid 3 the problem and fix http://youtu.be/Nyk4PWGVQgw


(i hope i have posted all this in the correct location)

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Yamaha xt660x 2009 blue/gold mods= iridium plug, stage1+2, removed snorkel, blocked ais, akrapovric pipes, power commander pc3usb (pre made map), adjusted tps, dynojet 02 optimiser 30amp aux relay, smoked puig screen, oxford heated grips and brembo carbon ceramic pads, rfx 30mm bar raisers, puig long adjustable leavers, plus much more and a cheep �30 alarm which stopped it been stolen