What really is the difference between a forged steel and a cast iron crank? I suspect the steel is stronger since from what I read it came in higher HP engines. Is that all? Are they interchangeable?

When I built a 350 to replace the 6 cyl in my 68 I bought a block and crank from a gearhead neighbor. He said they came out of a 69 truck and it was a steel crank. He told me a couple of ways to tell the difference but I forgot them. One I remember is the sound it makes when you ping it with a hammer. Steel has a ring but iron is dull I think.

Just curious. Thanks

You said it, the steel crank is stronger. A steel crank will have a 1/4 thick casting line, the cast will have a thin one.

The best way to tell the difference, especially for the novice crank spotter, is to match the numbers on the crank to the ones at Mortec or other lists.

SBC TWO PIECE REAR MAIN OIL SEALS


1130.......327.......forged..medium journal...3.25" stroke
1178.......302.......forged..medium journal...3.00" stroke
1181.......305,350...cast....medium journal...3.48" stroke
1182.......350.......forged..medium journal...3.48" stroke
2680.......327.......forged..small journal....3.25" stroke
2690.......350.......forged..medium journal...3.48" stroke
3279.......302.......forged..medium journal...3.00" stroke
3474.......283.......forged..small journal....3.00" stroke, military tank use
4577.......327.......forged..small journal....3.25" stroke
4672.......327.......forged..medium journal...3.25" stroke
310514.....350.......cast....medium journal...3.48" stroke
330550.....350.......cast....medium journal...3.48" stroke
354431.....262.......cast....medium journal...3.10" stroke
3727449....283.......forged..small journal....3.00" stroke
3729449....265.......forged..small journal....3.00" stroke
3734627....327.......forged..small journal....3.25" stroke
3735236....265,283...forged..small journal....3.00" stroke
3735263....283.......forged..small journal....3.00" stroke
3782680....327.......forged..small journal....3.25" stroke
3814671....327.......forged..small journal....3.25" stroke
3815822..265,283,302.forged..small journal....3.00" stroke
3835236....283.......forged..small journal....3.00" stroke
3836266....283.......forged..small journal....3.00" stroke
3848847....283.forged or cast..sm. journal....3.00" stroke
3849847....283.......forged..small journal....3.00" stroke
3876764....283.forged or cast..sm. journal....3.00" stroke
3876768....283.......forged..small journal....3.00" stroke
3884577....327.......forged..small journal....3.25" stroke
3892690....350.......forged..medium journal...3.48" stroke
3911001....307,327...cast....medium journal...3.25" stroke
3911011....307,327...cast....medium journal...3.25" stroke
3914672....327.......forged..medium journal...3.25" stroke
3923279....302.......forged..medium journal...3.00" stroke
3932442..267,305,350..cast...medium journal...3.48" stroke
3941174....307,327...cast....medium journal...3.25" stroke
3941178....302.......forged..medium journal...3.00" stroke
3941182....350.......forged..medium journal...3.48" stroke
3941188....350.......forged..medium journal...3.48" stroke
3949847....283..forged or cast..sm. journal...3.00" stroke
3951130....327.......forged..medium journal...3.25" stroke
3951529....400.......cast....large journal....3.75" stroke

Or you tap it with a hammer on on one of the weights. If it rings, it's steel. If it sounds like more of a clunk, then it's cast,

Since I was in the "Forging Busines" for 35 years, I can tell you the reason forgings are better than cast is "strenght" when steel is forged, it is hammered from billet steel that is heated to a temperature of 2300 to 2400 degrees. During the forging process a hammer will beat the billet into shape in a closed die, this changes the molecular structure forcing the molicules tighter and flow to conform with the piece involved. I have made many cranks in my day and they can be very difficult to make. I think Oldsmobile tried using cast cranks in the 1970 455s with disastrious results. Very easy to tell a casting from a forging by the trim line if you know what your looking at.

As previously mentioned, looking at the crank's parting line is the quickest, most determinate way without having to go through mounds of casting or part numbers somewhere.

Cast:
http://img141.imageshack.us/img141/4221/197a114a4ecastpartingline4zi.jpg

Forged:
http://img210.imageshack.us/img210/622/1971144enewestforgedcrank5fn.jpg

That shows it very well! Forgings are put in a trimmer to remove flash, thus the wider flash line...........

I wrote a short piece on this subject a few days ago under Engines entitlled Crank it Up.


Larger Dave