14 Jan 06 - CHT and Exhaust Temp Probes


Trying to get some of the engine probes in here, today. Wiring and baffles, from what some folks out there tell me, is something of a chicken and egg problem. Nice to have the baffles in there so that you know how to route the wires, but it's also nice to have the wires out of the way before you start messing around with baffle parts. I guess we'll cross that bridge when we come to it . . .


P1010012.JPG
Oh, the subpanel's in there. Had some trouble with the nutplates that mounted this to the side of the fuselage, so this only got in there after a bit of filing.
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Exhaust Probe and attachment. This is for the #2 cylinder, and is the only one in which the probe must be placed just a bit higher to avoid running into the locking mechanism for the exhaust pipe. (More about this below.)

Notes about this: ideally, you'll have all the temperature probes the same distance away from the engine. Because of bends in the tubes and wanting to make sure they don't hit the the locking mechanism on the tube (see picture above), it's not as an exact science as you'd really like it to be.

The goal, here, is to get all the probes about 3 inches away from the top of the exhaust pipe. That may be something of a random-sounding number, but after looking at other websites and documentation, that seems like it's about right.

Also, there is no guide as far as what angle you want to drill these. They shouldn't be sticking straight out (they'll run into the cowl) and should be drilled with some amount of thinking ahead to how the wires will be run. What I attempted, here, was to drill them so that the wires will be pretty close to the spark plug wires, so theoretically, those will be able to be bundled altogether.


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Again, here are the exhaust probes showing the angle at which they were drilled to facilitate running wires all over the place.
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CHT probe. Why the ruler? More about this below.

Notes about this: the way these fit in is the probe pictured (above left) slides into a hole in the bottom of the cylinder head. The spring keeps it pressed down against the locking doodad (I really don't know the correct term for this, sorry). If you have too much spring in there, it won't fit into the hole, and if you have not enough, then it won't be held as snug as you probably want it. The above picture is about the maximum amount of spring that you can get on the inside and still have it fit in there - you can adjust this by turning the locking mechanism that's on the right side of that picture, which then slides up and down the spring.


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Views of this in there - the CHT probe can be seen smack in the center, with the wire trailing down.
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Same thing, view from the front - front CHT probe is out of focus, and the back one is not.

More a note to myself than anything: this doesn't really feel like there's a seal that must be maintained (like, for example, the manifold pressure sensor or the fuel pressure sensor). I ended up using Fuel Lube anyway on the attachment between the CHT probe and the cylinder head, and looking back on it I'm not sure I needed to do that. Any opinions out there in readerland?




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