Thanks for the replies.
Freerider I used a portable bench jammed tight under the prop to stop it turning.
Gordo, Nod's set up might be different as the thread on the bolt is three inches from the head
after passing through an aluminium cone on my sail drive. I'm not sure enough heat could get through if it had been red loctite which needs 500deg F to break down.
I eventually got the bolt out after buying
a socket with a 6mm hex bit. Then using a sliding T bar to get even pressure on each side and a second pair of hands that used a hammer on the back of the socket with constant heavy tapping whilst I put more pressure on the nut it came undone.
The cone I could not get off eventually gave way after putting a pipe over a screwdriver to get more leverage. The movement I was getting was the give from the rubber hub in the prop I did not know was there.
The other cone was even tougher to get off! I snapped one screw driver twice, broke the largest allen key that would go through the cone, and bent other screwdrivers and a variety of bolts. I did try applying heat to the cone but that didn't help. I had tried penetrating oil
poured inside the hole in the cone after sealing up the other holes before some of the above. Then elsewhere on the net saw another struggler had used a pipe wrench. After removing the paint
and getting back to the aluminium so the wrench could grip, its a big wrench about 40cm long, and sliding a 60cm pipe over the handle with most of my 100kgs on the end the damn thing released.
The threads had a very hard light green material on them. Some kind of thread locking compound?
This thread is maybe why this was such hard work:
Losing Prop on Volvo Penta MD2030 Saildrive
And this modification made interesting reading:
First Choice Marine Technical Group