My first vehicle! 1956 CJ5

[bmorgil]

56willys, one thing about a rod knock, it doesn't go away. You can quiet it down for a short period of time but a true "rod knock" is a bearing spinning if its loud, or getting ready if its quiet. Knocking sounds from an old worn engine usually occur when they are cold and quiet as they warm up. Like gm said, the rod bearings and rod ends get out of shape and clearance becomes excessive. there can be a bit of "clanking" around and oil pressure drops off as clearance picks up.

You can drop the pan and check the bearings. However I would bump the idle up to about 700 - 800. That should give it some idle oil pressure. A lot of times a piece of carbon can get stuck in the combustion chamber and make a knocking sound, then go away. A good drive will fix that. If the knocking is most prevalent when its cold and seems to improve when it gets warm, it might be getting a bit worn. If it has good oil pressure, compression, the oil stays in the motor and the plugs aren't fouling with oil, rebuilding it is not necessary just yet. It is however a great experience! It is a solid lifter engine so a valve with too much clearance will "tic" loudly. As the engine warms the clearance will tighten up and the sound might change. I would experiment a little with the knocking sound and let us know how its doing. Be gentle with it till you know for sure. If it is knocking from wear and you put it under a good load, that is where the trouble will occur. If it is going to spin a bearing it will do it then. A spinning engine bearing is very loud. You wont wonder if it is something serious. You will know. There will be metal in the oil.