I'm not sure that I can be any more cautious than "having a go" on a wheel that is most likely destined for the dustbin anyway. If I broke it, I broke it. But if I learnt something in the process it was not a wasted endeavour.

To be fair; I have pointed out several times that I don't know what I am doing and am only learning this stuff as i go. That is why I have used inexperienced terms like "the bit the chain goes round". If I knew how to do it I wouldn't need any help would I.