Thank You Bruce & Deejay!!. I am astonished to have received such prompt and useful advice. The internet sure can be a wonderful thing. I have now paid my subscription and downloaded the manual for my Scott Bonnar 65. I had not realised that the cylinder and cutter form one demountable unit. The sprocket which I was stumped by screws off with a left-hand thread, and it is obvious now that the hole I mentioned is for a tommy-bar to unscrew the sprocket. I had regarded this mower as simply a utility item, but now I see that it should be possible to almost completely restore it, and I shall look after it much more carefully in future. The bedknife is quite sharp but rusty and probably would be best replaced. I shall post again when I have got the cutting unit out and examined it more carefully. Thank you once again.
MacCullum
