G'day Mike,
The single nut rear wheels are secured onto a taper with a woodruff key for location. It's an aluminium wheel onto a steel axle so we have a nice galvanic arrangement (!) and so basically the aluminium has probably corroded to the axle.
I have never removed one and have deliberately avoided doing so. That said I'd suggest gentle heating of the wheel and GENTLY trying to tap them apart. Tap the wheel as close as possible to the axle and definitely not on the rim! There are many war stories out there of ruined wheels from folks who have applied too much force with puller, press or hammer.
My two cents; if you don't NEED to remove the wheel, don't. If your trying to replace a tyre, I do them in situ.
The other thing I do is spray the area in question with wd40 of whatever jungle juice I have at the time whenever I think to in the hope that if I ever do really need to remove a wheel it may help.
I am a bit curious about you having single bolt wheels on an 11 HP machine. I thought it was only the smaller ones that had a single bolt wheel and the larger ones had the much nicer three bolt arrangement
