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I'm trying to Identify a crank someone wants to sell me. The only number I can find on it is on the first counterweight - 6223 and one at the other end of the crank which is GMT 56.
The only crank I can find that comes close to having any of these numbers is a 396 crank casting number 38566223 (last 4 numbers match)
You don't need much help; I think you've identified the crank. On crankshafts it is very common for the last 4 digits of the casting number to be used to identify the part. The "6223" crankshaft is, indeed, a 396 cid forged crankshaft used from 1965 until 1969. The 396 and 427 engines share the same 3.76" stroke, crankpin size and main journal size. However, there is a difference in the configuration of the counterweights on the crankshafts of the two engines. Consequently, as far as I know, they are not interchangeable, although a competent crankshaft shop could probably re-balance it to work. I wouldn't recommend this, though, as "Mallory Metal" would probably be required. By the time you're through, it would probably cost you more than just buying a 427 crank to begin with.
The "GMT 56" is a forging identification mark. "GMT" refers to General Motors Tonawanda. Tonawanda, New York is the location of the General Motors engine plant where all "Mark" series engines have been produced over the years and continuing until today. Tonawanda was also the location of a GM foundry and GM forge in the days when Corvette big blocks were produced, hence the "GMT" id mark found on castings and forgings produced there. The foundry, which is adjacent to the engine plant, was shut down in 1984 so no more "GMT" will be found after then. The forge plant was "divested" about 6 years ago when GM "spun off" its forging and most gear manufacturing operations to a new company, American Axle and Manufacturing. The "56" refers to the particular forging die set that was used to produce the crankshaft that you are looking at.
Probably a lot more than you wanted to know about the cranksahft!
The steel crank can either be a 396 or 427.The steel crank carried same casting numbers.The GM part number is what differentuates 396 or 427. They are not interchangable unless rebalanced. The crank in my 69 435hp is a 6223.I did the same thing you did and the information I just gave is what I was told. When I took crank and other parts to be balanced it was indeed an unmolested 427 crank. I just finished rebuilding engine 2weeks ago. Any questions please E-mail. T.M.
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