I have recently had to replace the head gasget on my TD5 defender. When I tried to start the engine for the first time it turned over a few times and then the starter motor jammed and just clicked away. I have not removed the starter motor during the cylinder head gasget change and have not had any problems with the starter motor before. The engine turns over by hand on the crank pulley as expected through the whole cycle of the 5 cylinders. The battery is fully charged. when I un-jam the the starter motor and try and start again it jams imediately. Any idea's please help!!