289 Otter Tube Threads?

[Dan Case]

Regarding Post 14:
AC Cars included the aluminum parts in the chassis builds. I don't know anyone that knows how they were attached. When made the part had a large round boss, lug, protection, or whatever AC Cars called it on its top surface. As installed in running Cobras the bosses had been crudely cut off. The tool used could have been a hack saw by hand or a power band saw.


Regarding Post 15:
As you see in my image there are no ribs or end beads of any type on original castings. Casting wise I know of only two variants; most have an AC Cars part number casting into them but some do not. Final installation wise every one is unique. The lug or sprue or boss whatever you choose to call it cast into the top surface was crudely cut off prior to car completion. There was a second hand controlled saw cut to shorten the down pipe section. Some of the copies I have noticed were cast copies of a used part warts and all. On them there was no lug to remove or no length modification perform. The best detail wise one I have seen was reverse engineered and recreated just like AC Cars parts. This more accurate copy required two saw cuts prior to installation in a car just as original parts did. After one of these gets used it would be impossible to know if it was original or not mounted in a Cobra. The clues that they are copies are in the screw threads and casting wall thicknesses which are significantly thicker than originals.


Regarding Post 17:
Calling them 'otter switches' is technically incorrect. They are thermal switches made by a company named Otter®. The logo shown below is on a generic switch with a black plastic potting, pressure injection molded, sealing feature of the electric internals. I have come across switches with red, black, and natural (almost translucent pale yellow now after all the decades) sealing. All known switches original to Cobras use red potting but be advised not all of this family of switches with red plastic centers are the correct temperature calibration for a Cobra's cooling system. I have come across two original variants for Cobras, one for early cars and one for cars after that. Both are marked with a 70°C temperature activation temperature (158°F I believe and that water leaving the radiator already cooled as much as it is going to be). Otter made switches of this style (design family) for several different type uses, including electrically operated automotive carburetor choke systems. They were made in many different temperature activation calibrations. I have been hunting originals exactly as fitted to Cobras since 1985 and never found one for a Cobra (correct every detail including temperature calibration) that was not in use in an original Cobra or with an original Cobra as a loose used part. A problem with the original Cobra application is that all the current for the electric radiator fan motor goes through it. The switches are a mechanical design. A bimetal spring changes shape suddenly as the calibration point is reached. The sudden operation slams the silver contacts together then in-rush current goes through them. I dismantled a switch that still snapped as the trip temperature was reached but it did not complete the electrical circuit anymore. The silver contacts were badly arc burned and hammered out. It not uncommon today to find original Cobras that are driven a little to a lot with either a toggle switch someplace for the driver to operate or a modern solid state switch mounted in some type adapter fixed on the water neck in place of the O.E.M. switch.