lawnmower motor magnet broken

I had a similar failure on a PM motor. The problem was that I could not tolerate much of a gap on the glue line. So, I cleaned both sides of the break with a brass wire brush and alcohol to be sure there was no loose debris. I used high strength epoxy and clamped both halves under as much pressure as possible using two pieces of wood and some glue clamps. Despite all this, I still had to sandpaper the PM motor ends to recover my clearances. 4 years later, it's still running.

Good luck.

Maybe you are confusing cause and effect. Perhaps the vibration caused the magnet breakage.

But to answer your question: Loctite 334 Structural Adhesive, High Performance, is designed as a magnet adhesive. But you probably will have gaps as you glue the broken pieces back in place, so use a good, non-instant epoxy. But recall that like poles repel each other, so the piece you replace will want to jump out. You will have to fixture it properly to keep it in place.

Used Araldite and made a wooden dowel to clamp it - works great!

Thanks