Easier to show you the difference, I think, than to describe it, John. Short answer... the parting line. Let me explain...

CASTINGS

Metal castings are made in a mold, and most molds have sections that fit together to create a cavity for pouring the molten metal into, to shape it. For Ford y-block cast crankshafts, I think two mold sections that fit together were used to make the mold with the shaped cavity inside. The two mold sections were made of sand conditioned with water and clay.

Where the mold sections fit together, when the metal fills the mold cavity there is a continuous narrow line in the finished casting. The line is referred to as the ‘parting line’,i.e., the point where the mold sections met. Basically, molten metal filled the line where the mold sections came together.

Sooo… look for a narrow line (like a pencil line) usually appearing on the crankshaft counter weights from front to rear.

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FORGINGS

Metal forgings are made in molds, too. The difference is that the metal to be shaped is only heated to make it soft (‘plastic’) so that it can be squeezed or hammered into the desired shape between two shaped metal molds (dies). For complex shapes like a crankshaft, a series of metal molds (dies) are necessary to progressively hammer the metal ingot (chunk) to the new desired shape. Each set of molds (dies) furthers the shaping process to refine the shape as much as possible before machining is required to attain the final shape.

Because the metal being forged is only soft, not liquid, the metal molds (dies) never come completely together in hammering the metal ingot (chunk) to shape. Because there are two molds (dies), there again is a parting line on the crankshaft. In the case of a forged steel y-block 292 crank,the parting line is ½ an inch wide in some places and wider in other places. The parting line is not in a straight line from front to back as it is with the cast crank. One place to look for the wide parting line is on the first throw after the front main bearing. The parting line is in the middle of the outside of the throw.

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Generally, forged parts are stronger than cast parts. The grain structure in a cast metal piece is random. The grain structure in a forged metal piece is designed to flow with the shape of the part in a chain-like manner. Too, the squeezing or hammering of the metal into shape compacts (compresses) the metal grain structure so that it is denser than a cast piece. Per volume, a forging weighs more than a casting.

A forged part costs more to make than a cast part. IF a metal part needs to be of minimal size yet as strong as possible, forging is likely the forming method used… like in making hand tools.

Hope this helps.

The oem cast crankshaft will have eight counterweights while the factory steel crankshaft has only six counterweights. As John mentions, the steel crankshaft does not have any counterweights at the center main journal.

John. Have you measured the main journal diameters? This would help to verify what you have if the crankshaft is indeed forged steel and not cast iron.