82' 300TD, 346k Recent valve adjust, reman injectors, glow plugs, diesel purge, etc etc.

She finally seems to have quit the idle lope and smoke, after today's purge and rack dampener adjustment - life is good!

However, on my all-out test drive this afternoon, i noticed a phenomena; one I have noticed before. 60mph, started up a fair hill, and slowly depressed the accelerator to the floor (but not though kick-down).

The engine was holding it's own fine, when suddenly, it started a, how should I describe it... metallic growl. As if the typical rattle of the diesel engine suddenly got 2.5 times as pronounced.

Maybe nailing? It stopped as soon as I let the pedal up a ways. I've heard this engine do that before, and all sorts of tuneup type work hasn't changed it.

It has only shown up a couple of times, and only under full load - after (?) 15 to 25 seconds (at full load).

Anybody else's 617 do this?

Probably cause?

...sounds almost like a piston is slapping the head...