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Thanks for that, I now have 3 to repair fortunately they are spares, will first need to remove the broken parts of the bolts left in bolt holes, drill and easy out I think better think on the drill bit I am using now lol

Good engineering practice stated that when you have a shear moment shuch as that the correct bolt to use is a Grade 5 or in metric an 8.8. Using a bolt of any higher tensile strength will mean that a lateral shear is far more likely to happen. A mild steel bolt would be much less likely to shear in that situation than a grade 8 or 10.10 or 12.9. The higher tensile strength is in its stretch over the length of the bolt and not the lateral strength.
A mild steel or 8.8 will deform a bit before it snaps.

Bloody hell I'm starting to sound like my lecturers now.

Cheers Rick, like your theory it makes sense, so far discussion has come up with stainless, 12.9 high tensile and now Mild steel, lateral movement and stretch. I think this is a great subject all arising out of a bolt.
However I think the subject is important due to the damage that can occur from failure, albeit I have seen these work loose before to have 2 shear I hadn't seen. I then went to fit a spare I had and further found another bolt had sheared within the bolt hole so now had 2 with sheared bolts in them. Please bear in mind I had not fitted these bolts originally and probably not fitted by Kawasaki either. So any thoughts are good on this subject and how to prevent recurrence. So all you techno phobics lets have the answers. And what about expansion and contraction with dissimilar metals helping these to come loose, am sure others on this site have had similar experiences

i also run a Vmax 1200 and they are murder for the starter clutch bolts coming loose,
the last time it happened the outer ring had fractured as well.
maybe its a harmonics thing in the engine, just a thought.

RickG wrote: Bloody hell I'm starting to sound like my lecturers now.

Yes Dad..