I don't know what's happened to my last post, I can't find it so here goes again. Thanks for all your replies about crankshaft nearside bolt. I solved the problem by making a strap spanner from a length of 1" x 1" oak ( yes you've guessed it, I am a retired carpenter/builder) with a length of webbing taken from the harness of an old strimmer, screwed and washered to one side. It worked perfectly.
After quite a struggle with the crankcase sides, which I removed with a homemade extractor, I have come to the final obstacle, the hexagon socket bolt inside the crankshaft. I have the allen key fitted with a long lever on the short end. To stop the crankshaft from turning I have passed a rod through the small end resting on the crankcase sides with (you've guessed it) two oak packings to protect it.
I have put enormous pressure on the lever and can feel the key flexing but it won't budge. Any suggestions please?