Lead - an interesting concept - on Bank Lines 76J6 Corabank Class the lead on the cranks was 9 degrees 28' but because of the differential stroke of the upper and lower pistons this translated to a difference of just under 2 degrees between IDC (Least combustion space volume) and TDC on the lower piston.As a cadet I sailed on a 76J6 in Bibby Line's Warwickshire, 1978 I think. Ran like a sewing machine, but was a complete pig to start astern. This was allegedly because as they were experimenting with increasing turbocharging, they gave her upper piston cranks more lead to get a bigger exhaust pulse. Of course going astern the timing was all to hell.... IIRC the lead was alleged to be 11 degrees, but as I only sailed on the one I don't know what a 'normal' lead was on a J type. I have to say I loved it as an engine, but I didn't have to change a combustion belt in that 5 months! Ahem.
The 76J4C Fish class had zero lead - the engine would not stop naturally at a dead spot, but if it was left in one position after maintenance it wouldn't kick on air and had to be turned to a more suitable position.