SOHC.co.uk Forums > CB350/400
rear sprocket nut torque question...
mattsz:
I'm mounting a new sprocket on the wheel, and I'm curious about the fastener torque listings in the Honda 350F - 400F service manual...
The four "final driven sprocket" nuts are 10mm, 1.25mm thread pitch - as are the "engine hanger bolt" and "rear suspension." In the 350 section (pg 75), torque values for all three of those are the same, 300-400 kg-cm or 21.7-29 ft-lb. But in the supplemental 400 section (pg 105), there's a change: the engine hanger bolt and rear suspension values match the 350 values, but for the 400 the same size sprocket nuts show a higher value, 400-500 kg-cm or 29-36.2 ft-lb.
Does anyone know why this was changed? I thought torque values were based on fastener specs, so matching fasteners would have matching torque values regardless of their usage - within reason, of course!
TrickyMicky:
Torque values will change depending on the workload of the pieces being held together, the material composition of the relevant pieces, not just the diameter of the bolt. Suspension and engine mounting bolts do not actually move, and the engine bolts are quite often screwed into alloy castings. The sprocket bolts are screwed into steel inserts mounted inside rubber bushes, and the whole lot spin round with the wheel so there are centrifugal forces to contend with. But don't forget that the sprocket is actually secured by a damn great circlip to the hub, on a nice new bike with no corrosion (ha ha), when the circlip is removed, the sprocket lifts of complete with the rubber bushes attached. Centrifugal forces are quite something to contend with, until the onset of modern hi-tec wheel fixings, I have encountered many large commercial wheels where the front left hand wheel nuts had a left hand thread to combat self-loosening.
Bryanj:
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!!
mattsz:
--- Quote from: TrickyMicky on July 04, 2020, 03:23:45 PM ---Torque values will change depending on the workload of the pieces being held together, the material composition of the relevant pieces, not just the diameter of the bolt. Suspension and engine mounting bolts do not actually move, and the engine bolts are quite often screwed into alloy castings. The sprocket bolts are screwed into steel inserts mounted inside rubber bushes, and the whole lot spin round with the wheel so there are centrifugal forces to contend with. But don't forget that the sprocket is actually secured by a damn great circlip to the hub, on a nice new bike with no corrosion (ha ha), when the circlip is removed, the sprocket lifts of complete with the rubber bushes attached. Centrifugal forces are quite something to contend with, until the onset of modern hi-tec wheel fixings, I have encountered many large commercial wheels where the front left hand wheel nuts had a left hand thread to combat self-loosening.
--- End quote ---
Sure... but why change the spec between model years if the hardware size, composition of the metals, and application are the same?
taysidedragon:
Matt, I guess that's what they call model improvement, learning from past experience, etc.
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