Increase compresson on a budget?
Balance the crank?
Fill a hole in the piston?
Safe place to keep that extra bolt so you know where to find it?
While I am the current owner of this AT1 engine I am absolutely not responsible for the bolt,
but it does make me smile everytime I see it.
Even more curious to know if it had a corresponding dent in the head? I have to admit, that beats my cigarette butt and nail headlamp spacer and bolt retainer hands down.