Well after tinkering with the machine today I have come to the conclusion that it just can't happen the way I was thinking. There's no way that gear can get out of the slot without the selector being pulled out of the head. I'm now thinking it must have been that way ever since I bought it. The machine was purchased from an old retired machinist who told me he had replaced the belts just before I got it. There would have been no reason to remove the selector for a belt change but maybe he did. I had to rewind the speed changer chain because he had it wound the wrong way so when you tried to increase the spindle speed it would actually slow down. Anyway it seems to work fine now so it's all been a bunch of to do about nothing. Guess I have to find something else to fix. Thanks for the replies anyway'