Does it look like a pully (with a rope knot holder in the side) but the aluminium covers it fully (eg no hole in the middle in the top), If so there is a steel hex coming out of the bottom of it and this has an internal thread which screw onto the top of the magneto/flywheel. Hope fully you can hold the blade disc and get a spanner onto the hex it is a standard RH thread. The 18 that I have has the cute little pull starter. But I have one of those pullys from a motor someone gave me. All the best. Daz
