Oil Pressure Sending Unit Mount

One of the advantages to cleaning the engine case halves in my utility sink with a toothbrush is that I get to intimately learn every little nook, cranny, crevice, boss, indentation and casting mark. One of my goals for this rebuild is to make as leak-free an engine as possible (for the last several years, half of my garage floor has had a continual pile of kitty litter absorbing the oil this car has leaked).

Anyhow, I noticed that the mount for the oil pressure switch (the sensor that triggers the low oil light - which I'll be replacing with an oil pressure gauge and sending unit) was at an angle. To be more precise, the mounting surface, which is sealed with a little copper washer/gasket, is not perpendicular to the threaded hole (due presumably to draft required to remove the pattern from the casting mold - I suspect the case halves were made with the plaster casting process (for those interested, here's the Wikipedia article about casting)). To get to the point, this angled surface prevents the sensor/sending unit gasket to properly seal.

This means another opportunity to use the Bridgeport! I threaded a tap into the hole, then used this as a reference to align the case half up with the milling machine. Once the tap was lined up with the centerline of the spindle, I was all set:

Porsche 914 case half on a Bridgeport vertical mill


After shimming and clamping the case to the table, I removed the tap and used an end mill to machine a nice flat mounting surface:

Porsche 914 case half being machined on a Bridgeport vertical mill


Hopefully that will solve one oil leak!

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All pictures and text copyright 2008