Greg,
Thanks for the reply. A couple of key things ( my apologies if I'm stating the obvious): Check the "slop" on the sprocket to shaft, movement. The keyway on mine was quite worn. Secondly, check the wear on the sprocket teeth.
If they are "peaked " you may need to replace the sprocket. Information required is: distance of peak to peak on the sprocket, width of the sprocket, length of chain required (this is determined by full starboard to full port) wire size, length of wire required and type of cable crimp required. (normally a sleeve type of crimp is fine). I found that to tension I simply pulled the wire tight and locked up the dog clamps. (must have 2) It's a 2 man job that requires a lot of patience and the introduction of a few new swear words!!!
Good luck and keep me posted,
Cheers,
Maurice.