Right I had a go at this again tonight, still no joy. I sorted all the earths out by taking all the paint off and welding a bolt onto the chassis as recommended. I took the starter off and tested it as well. I turned round by hand fine & I connected it to the battery on its own and it spun round no problem. I still however can't crank the engine by hand, like it's still stuck on something? I tried draining most of the oil out to see if that might help but nothing
