Is there any way to tell for sure if the crank on the left in the pic below is a 383 crank? It came out of a 400 that used stock pistons that were a mile down in the hole.

What made curious was the way the #3 journal looks. The radius from the journal surface outward is almost twice the height of a stock 1969 383 crank I have on hand for reference. Not sure if that means anything but I am wondering if the reason there is so much more material there is because it might be a 440 crank that had the journals cut down to fit into the 400? I know the #3 has the thrust bearings so that could account for it but again, it's almost double what it is on the 1969 383 crank I have for comparison.

A few of the throws look like they had some metal removed to balance it. This may have been because balancing stock 400 pistons that most likely came with a cast crank must have been a little difficult. The last rod journal is drilled all the way through but it looks as if that was done by a machine shop. I know forged cranks were drilled from the back but only part way which is the way the 383 crank is.

As is typical, there are no real part numbers on the crank except there is an "R" on the side of the first throw where the 383 crank has a "U" and the rearmost throw has a "7" where the 383 crank has a "56". See the pics for reference.

Thanks for any input.

There was a point when the thrust bearing diameter changed, got larger. Maybe that's what you are seeing. If it where a cut down 440 crank you wouldn't see stock (I assume 400) pistons a mile down the hole, they'd be pop ups and hitting the head.

http://440source.com/bearings.htm

I'm thinking if it was a cut down RB crank there would be a radius instead of an undercut where the journal meets the thrust face. '74 and later BB cranks had a larger 3.780" diameter thrust surface.

If still in doubt, measure the stroke.

Earlier manuals 400s still got forged crank. So... it could be?

Had to go back and re-check the deck height math but this is correct. The piston C.H. looks to be the typical 1.813" measured from the center of the wrist pin to the top of the piston. So 3.38"/2 = 1.69" + 6.358" + 1.813" = 9.861. Then 9.980"- 9.861" =.119" below the deck which seems on par for a late '70s 400. Guess I did it wrong the first time because I would have realized there is no physical way this combination of parts would have worked with a 3.75" stroke. Always a plus to know what you actually have.

Seems like the chances of it being an original forging from 1977 are slim but whatever, it's a factory forged crank in decent enough shape.

Thanks again for the replies.

It's been reported that some HD manual trans trucks with the 400 got forged cranks well into the seventies.

I have a 1976 400 out of a 4x4 4 wheel drive stick shift pickup that has a thin balancer on the forged steel crankshaft
I bought it for the block only, I may still have that crank, it spun a rod bearing or two and didn't look like it hurt the crank at all
If you want me to look at it and maybe post a picture of it I will

Several years ago I pulled a '78 400 out of a pickup truck with a manual trans. Had a steel crank and the backside of the bearings were dated '78.

Guess it's possible it's 400 forged crank? The truck was 2wd and originally a 318. Would 2WD, 4 speed big block trucks been equipped with a forged crank or was that a HD/4x4 application only?

Seems reasonable to presume the engine came out of a BB manual trans truck since it had the deep, rear sump pan though I have no idea if that was original to this particular motor or not. The truck was from out in Oregon which somehow retains more '70s trucks per capita than anywhere else on the planet so finding the motor and/or parts was probably fairly easy.

Original or not though, the motor was a strange buildup. There were some decent parts in it - aforementioned steel crank, nice recon'd rods with ARP bolts, milled 452 heads with positive seals and M.P. valves, .484" purple cam, Performer RPM intake, long tube headers, double roller timing chain, "Hemi" mechanical fuel pump, windage tray, HV oil pump and HD shaft...your basic '80s style "Mopar Performance" recipe street motor.

Unfortunately the guy kept the stock, low compression pistons in it and put it in front of a wide-ratio, granny first gear NP 435 with 3.23 rear gears which leaves you to scratch your head. The thing it did best was drink gas. It ran OK after a lot of tinkering but it was basically doomed from the start with the low compression pistons.

Good to know, latest I'd ever heard before was '76 but always suspected the forged units went up to the end of BB production.