340 Problems

I would say get it out of the car. Get as much of the fluids out of it as you can. Pull the oil pan off. Look for obvious damage first, ie: loose connecting rod, metal flakes in a particular area. If nothing is obvious, start taking main caps off one at a time, making sure you maintain the orientation of each cap. If you don't see a problem reinstall the cap and move to the next one. HINT: start at the back cap first. If you don't see any problems do the same with the connecting rod caps. Problems that you might see are grooves in the bearings or crank journal or a spun bearing. Get back to us with what you find.

Hope this helps

Jack