I just took a look at my timing chain on my series2/3 1974 88 and wondered how you tell how tight it should be to determine the wear if any? Its not what I would describe as taught (chain is still on the engine with tensioner etc) Its more like a fan belt check when you place your finger in the centre between the sprockets it does dip a bit. Any advice please much appreciated?

you dont check like that its tension will depend on the tensioner ,you can either check how far its retarded or lay chain on a flat surface and pushlinks together then pull apart measure the amount

Sounds good thanks James. When marking up the sprockets before taking the timing chain off is it essential to have the engine at TDC or not?