As Matt has said, on our Raven Tours the bolts have pointy ends and are designed to dig into the EBB so will leave an indentation in the soft alloy.   If small rotational adjustments of the EBB are made the indentations can become a groove and the eccentric is then not correctly locked.

On mine I can remove the bolts, look down the holes with a torch, and rotate the EBB to see where the next indentation is.  I have been lucky as mine had been adjusted properly by the PO and the indentations were well spaced apart - so I have simply reused those indentations rather than make new ones.

I have found that the bolts can loosen off so mine are now drilled and lockwired (others use bands made from innertube).   I also found that after 1500 miles in one position that the bolts needed to be wound in a touch further to take out a little looseness between the EBB and frame - the downward loads from cycling had pushed the bolts deeper into the EBB.

If you get new nuts welded on make sure they are fine thread M8, not standard M8 nuts.

Edited to add:
What I have written above is relevant to a Raven, looks like the Voyager may use a slightly different system with flat ended bolts??

Hey, just to let people know that this is still available.

I've been dealing with some family matters so apologies for the silence.

Mark

I agree with Dan, likely metric.  But there are fine threaded and course threaded versions, so if you get them out undamaged, measure the diameter and the pitch.  Your mechanic friends most certainly should be able to help.

If it is M8 X 0.75, you likely need this one.  That is the same one I use on my Nomad Mk II.
https://www.sjscycles.co.uk/bottom-brackets/thorn-m8-extra-fine-conepointed-screw-for-eccentric-bottom-bracket-shell/

One thing that has not been mentioned here, if you get them out and get new bolts, you should install the eccentric so that the thick metal part is the part that the pinch bolts press against.  If you set it up so the pinch bolts press against thin metal, it may deform, thus you want to avoid that.  See attached photo of mine, the thick part of the eccentric is on the bottom where the pinch bolts are, not the thin part of the eccentric.

Thanks a lot for all yours answers. I'll try to contact the man who sold me the bike and ask him what happened.

Some colleagues of mine are mechanic, I'll have some help of that topic.

Do you think that the threading is to be metric?

The welds holding the nuts on look to be crudely executed. It occurs to me that an alternative approach would be to carefully grind through them using a thin cutting disc and remove the nuts with the sheared setscrews in situ.  Either new stainless nuts could be welded on, with minimal damage to the paintwork, or an expanding eccentric BB shell could be fitted, if one of a suitable diameter can be sourced.