G’day Speedy
That’s my usual first move. I’m on first name terms with most of the people in my local bolt shop as I’m in there regularly getting stuff.
This nut has an unfaceted threaded extension that positively locates the starter cup with respect to both the flywheel/cooling assembly and crank. It both keeps it concentric with the crank and prevents the cup from being dragged longitudinally and working loose.
I’m either going to have to get one made or find a spare from another mower I think.
Ironbark
