Knocking series 111 diesel bit smoky too!

HI

I recently bought my first landrover, its an 86 series 111 2286cc, while busy doing some general refurb to doortops, rear floor , wheelhubs over the last few months it has been running Ok without smoke when warm!until last week when a knocking noise accompanied by greyish smoke on start up, this lasted until warmed up.
the knocking noise stops on low tickover but starts when revved slightly. it sounds quite worrying at a rate of perhaps twice a second.
i have had air in fuel problems recently, not sure if this could be part of problem this morning i too off sump to have a quick look, no loose bolts around and seems ok.
with engine running i cracked off the injector nuts slightly one at a time and with each one, this stalled engine.
previous owner did valve stem oil seals. Before i whip off its head any of you chaps heard of similar problems or any ideas on what it could be.

thanks

following a chat with mike the mechanic prognosis was it almost certainly an injector, keeping revs up i slackened each injector feed inturn and knocking stoppped on No3 a new britpart injector!
the out of engine test revealed a solid squirt rather than a fine mist, removing the nozzle the internal plunger seemed to be stuck , i replaced the new nozzle with an old spare and started it up and there it was no knocking