I pulled the crank out of my 71 340 this weekend for a refresh. The motor has been rebuilt once before. (Which I knew) The crank on the right is from my motor Cast# 2658278 All the things I find on the net say it is cast. But it sure looks like forged. If you tap it with a hammer it rings like a forged crank. The crank on the left is from a 71 318 Cast #2658393. The one in the middle is a 73 340 Cast Crank that they say has been shot peened cast #3462387. Is the one I pulled out Cast or Forged? The balancer is internally balanced piece cast #3614369. also the rods are for a cast crank #3418645. Has all of this been thrown together or is it right for the motor? I am taking it all to the machine shop on Wed. and want to take all the matched parts. Thanks for your help.

next picture

The wide parting line would indicate a forged crank as compared to the thin lines on the other cast cranks. I'm wondering if it could be a 318 truck crank which didn't have lightening holes in the journals. Don't know about the numbers, but process of elimination would point towards the truck crank.

273???

Which one should I use?

The 340 crank because it has less rotating inertia.
R.

the left and middle are castings.. the right one is a 318 truck (or poly?) for sure. Use the truck crank, and have the "rod pin" area drilled out to lighten...they usually knock about an inch (or so) hole there and cost around $150.

NONONO! The middle and right are forgings. That should be obvious. Look at the parting line on the crank on the left, it's sharp. Typical casting look. Both the center and right cranks have wide, ground off parting lines customarily seen on forgings. Also, check the shape of the counterweights. Forged counterweights have a more organic shape, they look like kidneys. Cast cranks have square, sharp corners.

Now on to reciprocating and rotating inertia. When MOPAR hung those monster 340 pistons on the ends of the rods on basically a 318 crank, they drilled the crankpin in order to be able to use the crank without external balancing. So any weight removed from the crankpin side, either by weight reduction of the rods, or weight reduction of the crankpin, or weight reduction of the reciprocating weight, allows the counterweight to be SMALLER.

Thus, the drilled crankpin allows for even less rotating inertia becase it doesn't take such a big counterweight to balance it.

R.

http://www.moparts.org/Tech/Archive/motor/8.html

Dennis

The middle and left crank are cast. I agree the one on the right should be forged but the number on it says it is cast. (which I do not believe.) the rods on it claim to be for a cast crank also. But, They are bushed floating pins.

Coincidentally, I was just doing a Google search for information on the same subject when I came across this thread. I have the same 2658278 crankshaft that came with a 1973 340 I bought and was trying to find out more about it. It too has all of the features of a forged crank like yours. It seems that the 2658278 part number may have been on both forged and cast cranks. If you scroll down on this chart to where it says 340 in the left column it lists the part number as a 68-73 340 steel crank.

http://www.standardcrankshaft.com/crankshaftkitcatalog.html?sid=4744

Wow! Exactly what I was looking for. Thanks!

Considering that the 318 steel crank list is exactly the same as the 340 steel crank list, it would appear that the list shows which like-material cranks will physically interchange without regard to original application or balance.

340 cast crank isn't mentioned probably because of it's rather short term of use. It should be late '72 and '73.

Well I'll be.......seeing my optometrist. Yes, the middle is a casting, for sure.

R.

Back in the day when NHRA was still racingmodified production cars john Diana told me to try and find a forged steel crank out of a Dodge truck 318-3 motor, it was a lot better than the stock 340 where according to him and the Mopar drag engineers No way I would use a cast steel crank when I had a forged steel crank to use OP, take it to your machine shop and have them magnaflux it to make sure it is still good, no cracks, and have them check the balalnce, if it needs fixing on the balance have them do it I no several NHRA stock class racers that took the 340 rods out and switch to 318 rods along with lightweight pistons, they sat several NHRA class records Light weight(rotating) is better than some heavy weight parts in our motors, as long as they will do the job without failing