- Mon Feb 18, 2013 5:20 am
#22441
Thanks Jack, i agree with that, was strange that a duplex in a enclosed and lubed space would shear like that.
Hi Robin,
When my dealer checked the primary chain tension, that I thought was too tight, he confirmed it was perfect; only about 5mm movement. If you think about it, there is no need to have more since the centres between crankshaft and clutch are fixed, whereas the secondary chain is adjusted with more play to allow for the fact that the swing arm pivot point is not at the same location as the drive sprocket. The final drive cush rubbers provide some softness in the system which also serves to protect the primary chain system. Note also that the primary chain tensioner is not spring loaded but fixed and only needs adjustment to maintain the standard chain tension.
The chain tension will vary due to the nature of a four stroke cycle, being a maximum when the fuel has been ignited and a minimum during the exhaust stroke. Energy stored in the flywheel helps to smooth out this cycle, but too much chain free play can only make matters worse.
Clearly a duplex primary chain has an ultimate tensile strength that far exceeds the load it is normally subjected to, so a simultaneous breakage of all four side plates is highly unlikely, in fact the plates must have broken at different times and only became apparent when the last two failed. I would suspect a material defect, some damage such as a nick in the side plate that could have propagated fatigue crack. Best advice is a new quality chain correctly adjusted. Cheers TrevorCH