I'm gathering parts for an engine rebuild and have come across a crank that is "supposed" to be an LS6 crank, but the machine shop Im going through says its a truck crank. The casting # is 7416. Any help would be great. Alex
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Re: C3 - LS6 crank?
Well, it COULD be both but I really doubt it would also be a truck crank considering it's a cross-drilled forging. Bet Joe L. knows for double-damn sure and can probably even tell you the name of the guy who made the thing. ;-) -
Re: C3 - LS6 crank?
The 7416 is a forged steel crank, used in '70-'72 LS5 engines - good piece.Comment
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Re: C3 - LS6 crank?
Alex-----
Actually, the 7416 forging was used in a variety of applications, so everyone is right. They were used in trucks, LS-4, LS-5, and some LS-6 engines. Other forgings were also used, though, for all of these applications. "3520" was another LS-6 forging. The 7416 forging (and the 3520) is made of 1053 steel which is the type used in all PRODUCTION and SERVICE LS-6 engines. The LS-6 versions of the forgings originally had tuff-trided main and rod journals; other versions of the 7416 forging usually did not. If the crank has been ground undersize, though, it doesn't matter; the tuff-trided surface will likely have been ground away. So, then there's no way to tell an LS-6 version from any other. The LS-6 version was known as GM PART #3963523; the other versions were known as GM PART #3993878 as well as other part numbers. However, these numbers won't be found anywhere on the crank.
GM also made a 5140 steel crank for 454 engines. It is identified by forging #3521 and was known as GM PART #3963524. However, this crankshaft was never used in a PRODUCTION or SERVICE engine. It is a SERVICE-only crank.
Oh, by the way, these crankshafts were forged at the old Chevrolet Tonawanda Forge and shipped across the street to the Tonawanda engine plant for machining. The forge later became part of the Saginaw Division. Later yet, it was "spun off" as part of American Axle and Manufacturing who still operate it. You may even find a debossed "T" on the forging. That was the symbol used for parts from the Tonawanda Forge or the Tonawanda Foundry (closed in 1984). Now you know the "rest of the story".In Appreciation of John HinckleyComment
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7115 and 6223 crankshafts
Joe - I have an original 7115 forging 427 crank coming for my 66 427-425. I know many original 427 cranks were the 6223 forging, but I see in Alan Colvin's Chevrolet by the numbers he mentions the 7115 was the 427 crank due to the counterweight thickness difference on the 3rd counterweight back being 7/8" vs 3/4" thick. He indicates this is thicker to compensate for the added piston weight which does make sense. Granted, anyone can later add weight by welding, mallory metal, etc to adjust. But, it does appear in my quest to find this 7115 forging, many,many 66 427's apparently did get the 6223 crank from Chevrolet originally. Assuming this is really true, what did they do in the factory to balance? Did they just drill it differently as far as balance, did they ever "weld" on mass?
Also, the 7115 I am getting is not underground on the mains or con rod journals...at all. I am hoping it will be straght and a simple polish and check is all that will be required. However, if it does need a grind, who can re-nitride (tuftride) the crank? I suppose it will be fine without, but is sure sounds like a great treatment to have. Will any of the aftermarket crank suppliers do this for a fee? I also believe that the 7115 is a cross drilled piece, with the forging of 5140 steel. I do have anohter 6223 crank in the engine that came in my 66....is this constructed of 5140 steel also or 1053?
Thx as always!....CraigComment
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Re: 7115 and 6223 crankshafts
Craig-----
The 7115 forging is, indeed, cross-drilled and of 5140 steel. It is also tuff-trided. I don't know of any field sources for this process, but I expect that they're out there.
The 6223 forging is of 1053 steel.
No metal was "welded-on" or otherwise added in the balancing process used at the factory at the time that these cranks were manufactured.In Appreciation of John HinckleyComment
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Re: 7115 and 6223 crankshafts
Thx Joe!...CraigComment
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