well I pulled the engine off the mower again and pulled the flywheel off.. bingo! you were right there is no keyway but there is a flatspot where it sits on the crank.. it had burred round! I must not have had the cutting plate done up tight enough.. I have used some quick steel and will try and file it up so that the timing is right again.. if not will have to get a new flywheel.... I would never had of guessed that could happen!!!