OK, so the usual CHT wells have been used by something else and you want to measure cylinder head temperature. If you have a Tanis Heater, it uses the CHT wells to heat the cylinders, or in my case, the Eagle EMS uses the aft two CHT wells to control the Fuel injection. This leaves you the choice of a Spark Plug Gasket type sensor or a piggyback sensor on the fitting that goes into the CHT well. The Spark Plug Gasket sensors are a bit problematic, and the Piggyback Sensors sold by Aircraft Spruce (Part # 10-03689) were the wrong type for my EFIS (K type VS J type). But the JPI piggyback sensors did give me a good Idea about how to make my own.
It turns out that making your own Piggyback sensors is cheep and relatively easy. All you need is some Thermocouple Wire of the proper type and a ring terminal.
You can find Thermocouple wire various places (E-Bay) and the wire contains everything you need to make a thermocouple. There are various Y-Tube videos on how to do this but basically all you do is twist the ends of the wire and tack weld them together. Presto you have a temperature sensor at the junction of the two wires for a fraction of the price of a store bought one.
The next trick is to put your temperature sensor in close proximity to your cylinders. A 3/8 inch ring terminal will do the trick (Aircraft Spruce part # 35112). You just need to insulate the thermocouple wire junction (electrically) from the ring terminal. Let me say that again. The thermocouple wires must not ground out on the ring terminal or it will not work. Don't ask me how I know this. Heat yes, Electricity no.
Don't use your normal ring terminal crimper here, instead use the Hex Crimper that you used for those BNC coaxial connections. The aim is to squeeze down the tube of the ring terminal enough to hold the wire in place without damaging the shrink tubing insulating the wire, because if the wire grounds out: It will not work.
If you have some Silicone Heat Sink Compound laying around (Part # 09-37450), you can use a little to help get good heat transfer from the cylinder to the Thermocouple Wire Junction you have made. *Note, not shown, there is a washer under the ring terminal to bring it up flush with the surface of the cylinder for a better fit.
Now plug in your (Heater, CHT Sensor, etc) in the usual spot and use some Fire Sleve to insulate it.
There you have it, a temperature sensor for just a few bucks and you made it yourself.
Roll Your Own CHT sensor
Linear Mode
