Hi Stuart, I need to get some background on how the engine became stiff to rotate. I see from one of the pictures that you have removed the crankcase cover. Was the engine stiff before you did that?

If it rotated freely before you worked on it, we will need to go over the steps in the work you did on it. If it was already stiff to rotate before you laid a spanner on it, we would proceed in a different way.

Is the oil sump filled to the correct level with SAE30 oil?