Connecting rod cap bolts.

[JV Puleo]

I'd buy all he has and look at them carefully. The threads should be sharp and the bolt not stretched... you might be able to come up with a proper figure for that by measuring several. The fact is, no matter what the originals were made of (it was probably a nickel steel), they lasted a long time and were suitable to the task. If you could find NOS Graham bolts I'd have no hesitation using them. You could also show them to a machinist and get an opinion as to their condition. Also, what were you using as a torque spec? In 1929 torque wrenches hadn't been invented. There are torque charts, but to use them you need to know what the material was. Tonight I'll look up what the SAE handbook says about that. I have a 1927 edition so it should be right for your car.

 

Good luck!

 

jp

[JV Puleo]

Here is the page from the 1927 SAE Handbook. The specifications themselves were  developed in 1922 so they straddle your era. I don't know how the two steels mentioned in the text relate to modern steel but you can probably find out. For purposes of torque numbers, I'd treat them as 3/8" bolts.

 

[hidden_hunter]

so is that book saying that there should be a level of commonality out there with some cars potentially? particularly around design?

[JV Puleo]

Yes, at least in that the Society of Automotive Engineers conducted tests, identified and codified materials and set standards for things like fasteners & wire sizes etc. There was no legally binding requirement that those standards be adhered to, but for the most part, they were. Virtually everyone involved with automotive design and manufacture was a member. The SAE standards were quite rapidly adopted right through the automobile and aircraft industry. Probably 99% of American cars largely conformed to them. While the process had begun earlier, one of the motivating factors for the rapid development of these standards was the huge problem the US Army Motor Transport Corps had during WWI with repairs in the field. With the wartime emergency behind them, it was decided that no vehicle would be bought by the government that did not conform to a set of standards, the earliest of which were for nuts & bolts. These weren't actually developed by the SAE. They were already in use, but their adoption by the SAE largely eliminated multiple versions of similar items. For instance, Cadillac used 12 TPI on many items... the early, one-cylinder cars used 1/2-12 bolts. At the time, 1/2" bolts were commonly available with 12, 13 & 14 TPI. The SAE standard was settled on 1/2-13 and the other two sizes largely disappeared.

 

Today, the commonly available American nuts and bolts are all SAE standard sizes although I suspect most people don't even know what the initials represent.

As new materials were developed, the standards changed so it is important to know what they were when a particular car was adopted. This page would pertain as much to your 1922 Cadillac as to a 29 Graham

[GrahamPaige29]

Very interesting.

[hidden_hunter]

9 hours ago, JV Puleo said:

Yes, at least in that the Society of Automotive Engineers conducted tests, identified and codified materials and set standards for things like fasteners & wire sizes etc. There was no legally binding requirement that those standards be adhered to, but for the most part, they were. Virtually everyone involved with automotive design and manufacture was a member. The SAE standards were quite rapidly adopted right through the automobile and aircraft industry. Probably 99% of American cars largely conformed to them. While the process had begun earlier, one of the motivating factors for the rapid development of these standards was the huge problem the US Army Motor Transport Corps had during WWI with repairs in the field. With the wartime emergency behind them, it was decided that no vehicle would be bought by the government that did not conform to a set of standards, the earliest of which were for nuts & bolts. These weren't actually developed by the SAE. They were already in use, but their adoption by the SAE largely eliminated multiple versions of similar items. For instance, Cadillac used 12 TPI on many items... the early, one-cylinder cars used 1/2-12 bolts. At the time, 1/2" bolts were commonly available with 12, 13 & 14 TPI. The SAE standard was settled on 1/2-13 and the other two sizes largely disappeared.

 

Today, the commonly available American nuts and bolts are all SAE standard sizes although I suspect most people don't even know what the initials represent.

As new materials were developed, the standards changed so it is important to know what they were when a particular car was adopted. This page would pertain as much to your 1922 Cadillac as to a 29 Graham

 

So in theory, there is potentially an interchange option for some of these cars

[JV Puleo]

Yes... in the same way nuts & bolts are interchangeable. Of course, the SAE Specs generally applied to materials and fasteners as well as a few other parts, like clevis pin ends & door hinges. These were "SAE Recommended." To what extent everyone adopted them was optional but I suspect the goal was to make it easier for suppliers of peripheral parts – the sort of things that all auto makers bought rather than made. I suspect that quite a few small parts are interchangeable.