The parts lists of Cailles show different methods of holding the piston pin. Some show a spring clip (circlip?) on each end, some models show a cotter pin on each end, some show a brass plug (button) on each end, and the 1927 Master 5-Speed Twin shows one brass button on one end and a cotter pin on the other end.
On disassembly of my Caille Model 30, I found a hole on one end of the piston pins that matched a hole in the piston boss (for a cotter pin), but no cotter pins were found. The hole in the piston pin is not all the way through – only through one wall of the pin. There was a brass button on each end of the pins. The buttons were a tight fit in the piston and they have a patent date on which indicates that they were factory made.
I’m wondering which way to reassemble: 2 buttons per pin, or buttons AND cotter pin. The brass buttons were rubbing on the cylinder wall according to wear on the brass but no marks on the cylinder. The pins are floating and were wearing into the brass, perhaps hitting the brass outwards until contact with the cylinders.
Apparently one rod had let go in the past since one rod has been replaced and there is some crankcase damage. Some metal pieces were found in the crankcase, now attached to the magnetic tip shown here.
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