How would this work?

[Scootertrash]

Here's another idea to hold the clutch in place while you loosen the nut. It probably wouldn't hurt to heat the nut a bit too.

[85_Ranger4x4]

It is locked:

Here's another idea to hold the clutch in place while you loosen the nut. It probably wouldn't hurt to heat the nut a bit too.

Problem with that is since the engine was out of the trike when I got it I just dragged it down in my basement to tune up over the winter so I can poke it in when it warms up outside...

I might just try to run it. It has been ran like this for awhile and it looks like it would be easier to fight with it in the trike rather than chasing it across the basement floor.

[Scootertrash]

You know what? Those marks looks suspiciously like the PO tried to remove that nut by using a screwdriver or a chisel or ? on the edge of the notch and then using a to bust it loose.

If it were me, once you get your socket, I'd heat that baby up good, not red hot, and use an impact and it should come right loose. Hell, even a Dewalt 18v or 20v impact driver or drill with the drill mode might be enough.

If I'm reading the manual right it's only 29-36 ft lbs of torque. Try the impact first, if it doesn't come off then, give it some heat. Another trick for tough nuts is to try to tighten them first, sometimes this works to break them loose. I know it sounds crazy, but it works.