SOHC.co.uk Forums > CB500/550

What do we see here?

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K2-K6:
It's quite an involved subject, changing material in relatively high stress application. 

The shape,  waisting, of the stud is not cosmetic but coincidental to it's function.  To fit in the space of the design it's an advantage to be smallest possible, that brings the stress it's asked to take closer to the material design limitations hence the higher tensile heat treatment and correct metallurgical composition to accommodate this.

The stud is then designed with a waist such that the root diameter is consistent from one end to the other with the threads sitting outside this. What this does is to allow the highest tension to be applied for the space available by evenly distributed stretching across each successive mm and consistent from one end to the other. If you increase the waist diameter that equilibrium starts to shift as you can't increase the root diameter of the threaded portion of the stud.
Now as you load it, the centre won't stretch (because the cross section is larger) to the same degree as the thinnest part, this accumulated difference is greatest as the diameter is forced to change going into the threaded section. This effectively overloads (all the stretch has to happen here) the material at that point and the tensile load capability can even go down as you've produced a failure point (shear coupling? ) with all of the forces directly focused at those two transition. Focusing it there can simply be more than that section will ever see ordinarily as the rest of the increased stud no longer shares the stretching.

What needs to happen is to increase the tensile specification of the stainless (loops back to material properties again) rather than change the cross section.

This is why bolts generally fail at the thread juncture if over torqued, the shape of them.

Trigger:
A good wright up K2-K6.
I don't think any stainless with do this job, even if you torque up to 18 ftlb and re-torque the compression will just stretch stainless. You have 4 hammers (pistons ) at 170 psi trying to push the head off. I think Stainless is just asking for trouble ;)   

Oddjob:
It's odd that the 400 cylinder stud doesn't appear to be waisted Nigel. I wonder why that is?

taysidedragon:

--- Quote from: Oddjob on April 04, 2022, 11:34:59 PM ---It's odd that the 400 cylinder stud doesn't appear to be waisted Nigel. I wonder why that is?

--- End quote ---

I'm pretty sure mine were.

K2-K6:
If the 400 doesn't use that waisted type it would likely be because the loading required is further within the capacity of the material for the 400. That smaller percussive effect of the cylinders takes a fair amount of load off the overall design compared to the larger engine.

I feel the stainless studs would creep too, think of it in structural terms as more like toffee  :) sustained load on it gradually deforms over time. The quenched and tempered steel very specifically produces a mild spring like property that is maintained even under loading.

Additional to all of the above (common I think to most of the bolts used on these bikes) the threads are rolled not cut with die or screwcut on a lathe. The effect of this is to effectively forge the threads into the steel structure such that the peaks and troughs are formed leaving no sharp cut into the material surface. This is much stronger and difficult to match by other methods, particularly critical at the thread lead out into the straight stud section.

They really did throw alot of pure engineering theory at these bikes, more from aircraft sphere than other fields (Sochiro was originally in that discipline I believe) which can be seen in the concept of these components.

Also why many "heavy duty" studs are just funny, they include all the faults Honda avoided in original design. Most, all? go with thicker is better claim, avoiding answering the material spec completely.

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