thanks Ian, didnt know snap-on did anything for less than 100 quid !!
I couldnt find one on the sykes-pickavant web site, they seem to do standard pullers only, but its quite specific for the BMW engine allowing the sprocket to be removed without taking off the timing case and holds the chain in position while the pump is changed
Got something now from 'Laser 4064 Diesel Injection Pump Puller' which fits the male thread on the sprocket (i was able to check as i have a spare sprocket on the pump I bought) and is the correct diameter to fit through the timing case..it is too short but a deep socket and a longer M12 extractor bolt will sort that out, 15 quid off ebay
thanks...