Could be wrong, as its hard to tell with the sound reproduced from a digi-cam and Utube....(Engine sound/mechanical noises lose just so much when recorded/played back.....)t

I have three running 617 (used and abused) engines. All have a similar noise to a greater or lesser extent.

If the oil-pressure is good When Hot at idle, and the Chain is good and timing of cam and pump as well as the cam and clearances,--you've already overhauled the injectors--

It aint gonna be a rod-bearing if you have at least 1.5 bar oil-press when Fully-Hot after say, half-hour run at idle....

I really wouldn't worry about it. It is after all, a 20 odd year old Diesel-engine. It aint gonna be perfect at that age, and by your own admission was not that well taken care of....(Some would say, what is expected for a 200 quid car!)

It seems (At least with every 617 N/A engine I've seen, as well as the 4 I've owned) that piston-slap to a greater or lesser extent depending on past use/maintenance, on one or two pistons is common at the ages and mileages we see now....

Give it a lube-change, and try a can of Wynns in it, or STP--May quieten it down...

You may find, that under load the knock is reduced--generally is if its piston-slap...

I have run a 300D N/A with a similar level of 'knock' to that shown for over 80K miles. It never seemed to get any worse, and still runs, but at 380 odd K is 'tired' (bit smoky etc...)--I keep it as a 'spare'

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Alastair AKA H.C.II South Wales, U.K. based member

W123, 1985 300TD Wagon, 256K,
-Most recent M.B. purchase, Cost-a-plenty, Gulps BioDiesel extravagantly, and I love it like an old dog.

W114, 1975 280E Custard Yellow,
-Great above decks needs chassis welding--Really will do it this year....