factory 340 forged crank

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Remember, the 273 and early 318 had the much lighter rods, so that's probably why the 318 crank was not drilled and the 340 crank was.
 
The 340 pistons/rods were new, big and beefy, rods +33g so to balance the crank they had to take the weight out of the throws...drill baby drill. The piston was 125G heavier by itself over the 318's.
 
Tap them with a steel hammer; the forged ones will ring with a long decay time. The cast one will thud
The one on the left looks cast.But I haven't seen a teener drilled , so I'm guessing it's a cast 340
The one in the center has a wrong sprocket on it for a 340, and a closed throw, so I'm guessing it's an early 318
The one on the right has a 340 sprocket on it, and is drilled so I'm guessing it's correct for an early 340.
I haven't seen a ton of cranks in my life tho.......
1969 Factory 340 pistons are listed at 719gms vs 592 for 318s, and 549 for 273s.
KB243 hypers for 340s,are listed at 585 gms,making the teener crank a natural fit

KB 107hypers for 360s are listed at 502gms, jus saying. I put the balance in the 340 neutral balance flywheel. They drilled a lotta metal out of it ,lol.
 
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AJ/FormS said:
Tap them with a steel hammer; the forged ones will ring with a long decay time. The cast one will thud
The one on the left looks cast.But I haven't seen a teener drilled , so I'm guessing it's a cast 340
The one in the center has a wrong sprocket on it for a 340, and a closed throw, so I'm guessing it's an early 318
The one on the right has a 340 sprocket on it, and is drilled so I'm guessing it's correct for an early 340.
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They are all three forged. You can plainly see the wide parting line on all three.
 
I saw that too, but I haven't seen a forged crank with as sharply defined edges on the CWs as the left one; so I mentioned the ringing as no one else had yet.
And again, I haven't seen but maybe a dozen SBM cranks and all were 68 to 73, except for the spaghetti crank I have from a 65-273.
Also, I weighed all my cranks one day, and the forged 340 cranks were all about 55 lbs, while all the others were lighter. I can't recall the difference tho.....
 
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I have cast cranks and forged cranks and 1 cast crank with a narrow parting line rings nice, not as loud or high pitch or as long as a forged crank. If you have a crank that goes thud it is cracked.


also the thicker counter weights have a lower pitch and don't ring as long
 
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They are all forged cranks, I have cast cranks also there is a big difference just buy looking at them, the easiest way to tell is the sharp edges.
Second part of my question what one is better today. From what yellow rose said, I am thinking the 318 crank is a better choice now a days. Building I nice street motor
10.1 to 10.5
318 forged crank (not a 340 crank)
A good I beam rod
Nice light weight piston
I would think this would be easier to balance.
what do you guy thing
 
On the early 273 cranks, The flange on the back is smaller for torque convertors I believe. Not sure about the early 318?
 
brian6pac said:
I have cast cranks and forged cranks and 1 cast crank with a narrow parting line rings nice, not as loud or high pitch or as long as a forged crank. If you have a crank that goes thud it is cracked.
also the thicker counter weights have a lower pitch and don't ring as long
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I noticed that one of my cast 318cranks also rings, but the decay time is a lot shorter just as you describe. Yeah maybe thud was a poor choice of words; I just meant deader than the forged units.
 
moper said:
Might have to do with the crank castings themselves. Or the material. Better iron is heavier. I'd say it's probably balancing issues but that's a total guess.
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Just to be clear these cranks are made from a steel billet and forged into their rough shape then machined... no castings or iron are involved.
 
davescuda said:
On the early 273 cranks, The flange on the back is smaller for torque convertors I believe. Not sure about the early 318?
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The pilot hole is a different size on earlier cranks... the change was made around '68 IIRC. The flange is about the same. Someone here will have the exact date.
 
The holes in the end journals are for balancing the heavier 340 piston weights as has been said.

Putting a hole there (think of it as 'anti-weight') does the same thing as adding more weight/material to those big end counterweights on the opposite side of the crank centerline, which is where the extra weight would normally be cast to balance out those heavier 340 pistons. But they ran out of room inside the crankcase to add that needed weight, and so used some 'anti-weight' on the opposite side of the crank centerline to do the job.
 
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Krooser said:
Just to be clear these cranks are made from a steel billet and forged into their rough shape then machined... no castings or iron are involved.
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Actually, the initial step of a forged crank is to cast the initial rough shape; the next step is to use the forge to force it into the final rough shape prior to machining.
 
davescuda said:
Another question. Is it better to use a 318 crank in a 340 if you use the new light weight pistons and I good new I beam rod?
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The forged 340 will be stronger but the general agreement is that the cast cranks (318, 273) will take 400 to 500 HP.

An early 318 or 273 crank will need around 80-90 grams off of the end counterweights for KB243's and SCAT rods. That is a bit over 2 teaspoonfuls of iron off of each one. It should take a bit over 3 teaspoonfuls of steel off of the 340 crank's end counterweights if you use that same piston/rod combo.
 
nm9stheham said:
Actually, the initial step of a forged crank is to cast the initial rough shape; the next step is to use the forge to force it into the final rough shape prior to machining.
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Nope... the cranks start as a round steel billet heated to white hot then hammered into shape... some are twisted some are not.

 
Always some confusion on billet cranks, too. Billet cranks are carved out of a steel billet much like the raw billets that forged cranks are made of.

Cast steel cranks are just that cast in a mold at a foundry then machined.

If you look at other videos showing the machining process that a quality crankshaft goes thru you will see the difference between a 'good enough' import piece and a high grade crankshaft.

Back when I was hauling a lot of auto parts from '98 until the early 2000's I did a few Lunati runs where I picked up raw forgings from the supplier in the Detroit area and took them to the heat treat facility in Lansing, MI. From there they went to Lunati for final finishing. I had a hard time not grabbing a crank or two that didn't pass the heat treat test... they were dumped in the scrap bin to go back and start from scratch.
 
Heres pics of crank in my 70 318. 1&2 throw is drilled. You can also see machine marks by the rod bolts?? Only on 1st throw.
Then groove in the last 2 throws. Also hole drilled in last throw.

20171027_113756.jpg


20171027_113736.jpg


20171027_113945.jpg


20171027_113954.jpg
 
yellow rose said:
What that video calls a billet I call an ingot. When most people speak of a billet crank it's meant as a machine round bar that is machine finished.
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From what I know from years hauling steel an ingot is a piece of material that will be melted and used in the production of a final product. A billet is a large round bar or square bar ready for machining or forging.

Semi-finished casting products - Wikipedia
 
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