HELP! What's this bolt for????

Hello All, When replacing my dizzy cap and rotar arm at the weekend I found a sheared off bolt inside the big hole which is covered by the rotar arm! It looked like it had been like that for a while as the sheared end was not shiny in the least. Is this a critical situation? The rest of the bolt appears (I got a small mirror to have a look) to be in place.... Hope someone can shed some light... Cheers

Most likely has been screwed off by a gorilla somewhere in the past. Most bolt shear failures are never shiny, they are normally a dull coarse grained silver grey initially and often don't develop rust unlest immersed in water.

I have been advised I'll need to have the other end removed via a stud extractor. Am looking for a someone with the skill to do this in the Edinburgh area. Do a you or anyone know of one?