65 Forged crankshaft Inspection Markings

[Jim V.]

As part of my original 300hp autopsy I have the following FYI...The pic below shows the original paint inspection mark on a June 65 build 300hp motor. The color appears to be the yellow/orange type color also seen on steering gears. The crank also shows the GMT (tuftride mark?) and the 2680 casting number as well as the wide (1/2in) casting seam all indicative of the forged steel crank.

[Joe L.]

Re: 65 Forged crankshaft Inspection Markings

Jim-----

The "GMT" does not refer to Tuftriding. It refers to the General Motors Tonawanda Forge where most GM forged crankshafts were manufactured in those days. These crankshaft forgings were then shipped to Flint or the Tonawanda engine plant for machining and installation into engines. For Tonawanda, they didn't have to travel very far. Although no Corvette small blocks were ever machined and assembled at Tonawanda, a lot of other Chevrolet small blocks were. Until 1968, virtually all small blocks used forged cranks.

The Tonawanda forging plant still exists. However, it's no longer part of GM. It's now part of the GM spin-off company American Axle and Manufacturing. AAM relieved GM of all of its forging capabilities. Since that time, GM has had no in-house forging capabilities, at all. All forged pieces are now out-sourced----to AAM or others.

So where do all of the CAST crankshafts that GM has used in most engines since 1968 come from? Virtually all are manufactured at the GM nodular iron foundry in Defiance, Ohio.

[Jim V.]

Re: 65 Forged crankshaft Inspection Markings

Thanks Joe...your knowledge of such things is amazing!

So...what do you think the yellow inspection marks meant?

Also, were all 2860 cranks tuftrided?

JimV

[Jim V.]

oops...2680 rather n/m *NM*

[Mike McKown]

Re: 65 Forged crankshaft Inspection Markings

The 250 and 300 horse cranks were not tuftrided, nitrided or otherwise hardened. The 350, 365 and 475 cranks were. My recollection is the yellow striped is appropriate for a non-hardened crank. The hardened cranks had a swatch of blueish green paint.