That’s a very substantial difference in diameters … but presumably Mr Honda knew his stuff.

I would be inclined to follow his example regards material specifications.

Are there any markings on the original bolt ?

MichaelG.

How does the mass of your AJ compare with the mass of the Honda the brake came off?

For safety related applications, I always recommend buying a manufactured bolt or stud.   Apart from Honda doing the sums, choosing the right grade of steel, and testing, their threads are made by rolling, not by cutting.   Rolled threads are considerably stronger than cut ones because rolling strengthens the metal by compression and leaves fewer stress-raisers.   Stress raisers cause rapid cracking when a highly loaded thread is vibrated, making cut threads a poor choice for brakes and aircraft wings!

The advantage of a lathe cut thread is it can be made to almost any size, and they’re plenty good enough most of the time.  But they’re not suitable when the strength and reliability of a stressed component is important.   More to making a strong thread than getting the right steel – rolling is a much better process, sadly beyond most workshops.

Dave

Metric Bolt Grades to consider.

The most common metric bolt grades include:4.6: Basic low-strength bolts.
8.8: Medium-strength bolts suitable for general applications.
10.9: High-strength bolts used in critical structural connections.
12.9: Extremely high-strength bolts for demanding applications.

More strength often means less ductilty. If something is strong enough in mild steel, no point making it from anything more exotic, not that I’m suggesting it’s mild steel. Before deciding what material, work out the stress.

I was thinking about fitting inscrutable Honda 500 180mm brake shoes to my Warco round column mill as a spindle brake.

Truly universal 😀

best

Robin

Fair response, Duncan

my thinking was that we could [either figuratively or physically] suspend a mass representing bike plus rider … from a linkage equivalent to the rolling radius of the front wheel jointed to the torque arm … and then give it a jolt or two.

I’m guessing that the low-grade M8 bolt might take the static load, but fail after a few cycles.

MichaelG.

Looks as the use a Free Body Diagram would be useful to consider how the Forces are applied.

Maybe look at EN16 T & EN24 T which I seem to remember  being an ideal choice for this sort of application.

Just an observation on this post. We have been concentrating on the material of the fastener, but perhaps we should also be considering the material that the fastener pulls into. The Honda set up is into an aluminium alloy of unknown specification. The AJS is into a steel bush cast into the aluminium alloy again of unknown specification. Going straight into aluminium will reduce the torque loading that can be applied to the fastener.

Are there any torque loads given for these fasteners? That might give you a starting for the selection of materials. I assume that the M8 is ISO coarse, but you have not given the thread form for the British bikes.

If I were designing this fastener I would most certainly choose a rolled thread for the reasons already given, and I would not be using a 12.9 as it is too hard to cold roll and you do not want to heat treat after rolling. Remember, this is a “Safety Critical” item.

Neil

Maybe a good place to start:

https://youtu.be/VHd_eSXwbIc?feature=shared

MichaelG.

You may well think that, Nick

… but we were asked about the fastener.

MichaelG.