Another Arctic cold snap in Chicago so I’m inside doing some research just to satisfy curiosity.
Studying parts catalogues, I find that SS and Jaguar used slotted nuts and split cotter pins in connecting rod bolts from before 1938 to about 1968, when they changed to a different bolt with a self-locking nut. Not sure about the side valve cars because the parts aren’t listed separately.
Counting up yearly production figures in Clausager’s Jaguar, a Living Legend, leaving out pre-'38 and post-'67, this adds up to a little over 316,300 engines, mostly six cylinders with some fours, or about 3,700,000 cotter pins.
For pushrod engines the slotted nut was part C.358 size 3/8"-20 BSF, and the split cotter pin was part L.103.5/8U for all 4 and 6 cylinder engines.
For the XK engines, the slotted nut was part C.2361 size 3/8"-24 UNF and the same L.103.5/8U cotter pin was used up until the change to self-locking nuts beginning with the Series 2 E-Type and XJ6. The 3.4 3.8 S-Type catalogues list both and mentions that the one supersedes the other.
We learn from the XK120 parts catalogue that the L.103.5/8U cotter pin was size 7/64" diameter and 1" long and called the “Drivopen” type, which was a brand name from Nettlefolds of Birmingham.
Cotter pin length is measured on the straight shank excluding the loop.
98338A734_ZINC-PLATED STEEL COTTER PIN.pdf (117.6 KB)
The hole in the C.3944 con rod bolt measures .120" diameter and the slot in the C.2361 nut measures .109" wide, so the pin is a snug fit.
Here are a couple of interesting rod bolts with a copper coating from a 140 engine.
The correct size cotter pins for SS and Jaguar engines can be obtained from McMaster-Carr www.mcmaster.com part number 98338A734 in a pack of 100 for under $5.
Here is the correct method to install them in con rods.
The slots in the slotted nut are a little difficult to see in this view, or it may be that this view taken from an aircraft manual is of a castlellated nut which is not quite the same as a slotted nut.
I wasn’t able to find an original patent for the slotted or castellated nut, so it may date from the mid 1800s. The earliest patent I found was #1283346 for an improvement in the slot shape dated 1918, which unfortunately does not refer back to previous patents.
I am merely passing along what I thought was interesting factual engineering information, not opinions intending to (nor interested in) starting any arguments.