SOHC.co.uk Forums > CB350/400

rear sprocket nut torque question...

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TrickyMicky:

--- Quote from: Bryanj on July 04, 2020, 03:58:25 PM ---Not just the front one, when comercials had taper seat wheel nuts all lh ones were lh thread, now they have spigot mounted wheels with integtal washer flat nuts and all are normal thread
You want to see the size of the torque wrench for those!!

--- End quote ---
Oh Yeah! 460ft/lbs if I remember correctly, and weren't they a ba---rd to remove after they had been on a while!

mattsz:

--- Quote from: taysidedragon on July 04, 2020, 10:33:52 PM ---Matt, I guess that's what they call model improvement,  learning from past experience, etc.

--- End quote ---

Guess so...


--- Quote from: TrickyMicky on July 04, 2020, 10:47:46 PM ---Oh Yeah! 460ft/lbs if I remember correctly...
--- End quote ---

 :o

K2-K6:
The difference comes from how the torque is used along with the structural design of the components. Although torque is seen as the constant ( the numbers make it look comparable across diverse fixings) it's application can be completely different.

As an example,  the cylinder barrel/ head stud is set within a very specific torque range to provide an even tensile loading from one end to the other,  and within the material's elasticity.  It's most easily appreciated if you think of it as a very strong bungee strap as often used to secure luggage.

The rear wheel assembly has mostly (spindle,  sprocket fixings etc) that are not pulled into elasticity to anything like the degree given in the previous example.  They effectively have the material in the fixing structure able to be tightened sufficient that it clamps the components it's trying to secure (leaving them in location to work in a shear plane as opposed to tensile) prior to going into stretching.  In this way the components remain way inside their structural elasticity,  but the securing nut ultimately gets compressed during torque loading.  This results in the nut's thread pitch reducing and providing a mismatch to the pitch on the bolt, as this happens the nut gets harder to turn as the differential pitches start to bind against each other.  It's this that you are measuring with the torque wrench (same as first example) but because you're only compressing the nut and not effectively stretching the components you're tightening, then there's effectively spare capacity to revise the torqued level.

The difference to the cylinder stud is that to raise the clamping on that you have to increase the within elastic total capability to revise, whereas on the sprocket one an appreciable gap to ceiling load is present.

As to why they did it,  probably durability trials on the 400 during r+d showed a loosening that they needed to respond to.  Discussion with the design engineers would allow them to evaluate if they could safely up the torque or would have to go for a redesign.  We can see what they agreed on with the spec change.  It does mean that it could also be applied to the 350 installation,  but the text obviously stays the same as already published.

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