Wow. I deeply appreciate your quick and insightful responses.
It is usual for anyone new to introduce themselves in the intro section before posting for advice.
A thousand apologies for my bad manners!!!!too much zeal on my part.
My name is Mark from Nairobi Kenya. I am one year old into owning a disco td300 (we call her mammoth) which I have been lovingly fixing. I got her with a good engine but everything else was mostly held together with superglue and wires!!! (and whatever else that was secured was threatened by a horrible death wobble). She is now running very well and have been quite impressed with the performance - save for the need to learn very fast about the various issues that come with owning a landie. I now use the td300 as my everyday car to shuttle my wife and I around this beautiful rugged country. (I have clocked about 30,000km in the last year)
Having been impressed by the td300, I wondered how its upgrade would be like to own and this is what led to this current issue with the td5.
Trouble set in when the car started overheating 300Kms from home (had to flatbed her back home). My mechanic established that it was the oil cooler that had issues(the coolant and the oil were mixing). We replaced the oil cooler (no more issues there now) but on assembling back the engine the car developed the knocking noise.
ps. Sounds like one of your valves
We have removed the cylinder head twice trying to check if valves are coming in contact with the pistons and they look ok. No marks on top of the pistons.
youll have to look under rocker cover ,you can refit cover without replacing gasket,if you leave old gasket in place for the time been ,worth running engine with ancillary belt off 15mm spanner needed to pull tensioner back
We have tried that too - running the engine without the rocker cover and the ancillary belt, but the sound is still there.
Darkness has set in. Will check the crankshaft pulley tomorrow morning.
Thank you everyone again and I will keep everyone updated on the progress.