Having bought a 58 NH basket case as my introduction to Ariel motor cycles the build has gone reasonable well until i tried to fit the outer primary chain case at which point the engine refused to turn over. Having now repeatedly stripped the clutch introduced additional spaces, assembling it with and without the chain etc, all to try to find out what was binding. Finally I convinced myself that it was the length of the spacer on the crank, only for a friend to suggested "you have got the chain wheel on the right way round?"
Ohhhhh! did i feel foolish when reversing it the problem disappeared. so whilst it has delayed me for a couple of weeks I now have a bike that is ready to be timed and then !!!!!!!!