The early vortex had a different disk with very short blades. It was pressed steel.
Have a couple here but dont have a pic.

The later Vortex (and the V40) had the 'turbo disc'. It is flatter than a regular oval disc and it has a large black rubber fan bolted to the disc. I think it was also used on a couple of different steel base models.
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And minus the rubber fan the disc will work on a full crank utility with the short blades, the handle bolts foul on the normal oval disc. The early utilitys had a smaller round disc and longer than normal blades.


There is nothing to stop you changing to a regular oval disc.
I would also suggest you try a later 4 blade disc as well.
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The regular oval disc with the later high lift/mulch (the wide ones) blades goes ok too. Just two of them is enough to blow the back door part open at full song. So the blades in the pic above on a normal disc.