You've been asked several times, and haven't answered- - - -DO THE RODS HAVE DIPPERS? If not you've got a full-pressure engine. Also, if the rod journals on the crankshaft have oil holes, it's a pressurized-rod engine. The babbit-pounders have troughs built into the oil pan, and dippers on the rods. A cracked piston skirt, bent connecting rod, or worn wrist pin hole in the piston can all cause a "rod" knock, or even a piece of broken piston ring lodged in the top of a piston hitting the head can cause a knocking noise.
Generally, it takes .005" or more clearance to make a knock audible at idle. The rods might rattle a little at light load just before shifting to a higher gear with less clearance, but a knock at idle needs a pretty wide clearance to be noticeable.
Jerry
