C3 - 350/270hp block markings ?

[Jim Callan]

On the pan rail, aligned with each bore, is the alpha character "J", "G", or "H". What does these mean?

Just curious, thanks

Jim

[Dick W.]

Re: C3 - 350/270hp block markings ?

I have been told various things, such as dimensions for cylinders, main bearing bores, inspectors ID, etc Maybe Michael Hanson or John Hinckley will elaborate

[Michael H.]

Re: C3 - 350/270hp block markings ?

Dick,

John Hinckley was at the Flint plant so he would be a better source for accurate info on this but I remember these as being cylinder size for piston fit. They would have been a little different in the 60's as they used numbers instead of a letter code. Generally, I think there was a 9, 10 or 11 stamped on the pan rail for each cylinder.

[John H.]

Re: C3 - 350/270hp block markings ?

Those are bore size codes, stamped in the pan rail at the air-gaging station at the head of the assembly line; early in the V-8's life, there were as many as eight toleranced bore sizes (for one nominal bore size), which were broadcast to the rod/piston subassembly area so they could prepare the correctly-matched ringed pistons and rods for each bore. This came down to four or so toleranced sizes in the late 70's and 80's, and with the advent of the LS1-series engines and their vastly-improved machining methods and process controls, these days there's one bore size and one piston size.

[Jim Callan]

Re: C3 - 350/270hp block markings ?

Thanks, out of 8 bores there were only 3 different codes, I guess that is a good thing. I was curious, anyway all 8 are 4.030 now.