Quote:
Originally Posted by 1985 CCX
Dan knows best!
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Best? Not so sure about that. I do spend a lot of time analyzing original parts, materials, and methods. I have a pretty good handle on what A.C., Continental Cars, and Shelby American did for many but not all subjects.
On fabrication:
A.C. was pretty consistent in cutting out and forming parts. To make one set of repair parts we had to create a wing bender tool set to go from flat blanks to exact matches of what A.C. created. Making welding jigs for create exact fit replacement subassemblies was required also. A.C. sheared, punched, welded, and drilled with jig fixtures.
Shelby's works was not consistent in much of anything I have studied. Shelby’s crews hand sheared, sawed, filed, ground with a grinder, free hand drilled, free hand turret punched, and used a belt sander to shape and deburr parts such that some street and race parts were each a one of one piece. If it looks precise and pretty Shelby’s works probably did not do it. I have a collection of factory drawings Shelby American created for parts they provided. So far, I have found that you cannot use any one of them to make an accurate copy of what they made. The drawings are suggestions and in some cases their math does not work. The only one that has caused me problems is the levers the team made for Weber carburetors. The levers were saw cut from flat stock, if bending was required the piece was heated with a torch and manually bent, and connection holes were sometimes in good places and sometimes not. In comparing notes around I learned it is not uncommon to have to relocate a lever hole for one or two carburetors in a set of four between 0.005 and 0.020 inch to prevent binding and or get great flow balance. I moved a hole in one lever 0.005 to get the right rear carburetor in our 1964 works system to be free of binding and get the last bit of balanced flow at idle.
Machine work:
A.C. was very consistent. Since 1984 I have measured and reverse engineered an assortment of their small parts they made themselves. Part to part variability at 73°F and 50% RH is usually on the order of a few ten thousandths of an inch to maybe five thousandths of any inch depending on what the part was until a revision was made. I bought more and better measuring tools to measure as well as they made parts. Yes, designs and dimensions of some items changed over time and some might confuse a planned change as sloppy manufacturing. If I use the standard deviations I find in their parts as basis to set drawing tolerances they catch machinists’ attention as being very tight in many cases.
Shelby American: Not so precise but the only one I have had to do something about was for carburetor levers.
In general most of the fabrication and machine work A.C. did was very consistent and yes they made planned changes as required over time. The same could not be said for some of the items like coachwork suppliers provided. Shelby American parts were usually quite variable for some reason or another. One reason was in many cases what team Shelby American used and what was sold to customers was different a little to a lot. To be fair, Shelby’s folks changed many things on purpose every time or most every time because they wanted to. As topics, the two best fabrication examples are steel racing rocker arm covers and steel
oil pans. Shelby American famously did their own fabrication of them and as a result there may not have been any two sets of rocker arm covers or any two steel
oil pans exactly alike.