Combustion monitor wires on a 1413 2.

G

Gary Brink

New member
My combustion monitor wires have been cut off and shortened. Am I correct that they need to be a specific length in order to give an accurate reading? If so, can anyone tell me how long they were originally?
Thanks,
Gary
 
what's a "combustion monitor" ?

EGT?
CHT ?

CHT probes are made in specific resistance ranges... but contrary to what was recently stated here
the lead length isnt critical unless you panel happens to be 100's of feet aft of your engine.

otherwise.. I dunno. :roll:
 
Hey Gary, if the EGT is working as it should , wire length no problem. If the EGT needle goes up as you lean all is fine. Lean until engine begins to run a bit rough (peak EGT 1200 to 1600 degrees) then richen the mixture approx. 50 degrees and you are at best power. CHT should be 400F or less. You are the combustion monitor. If the wires have been cut too much the needle will go off scale at peak EGT. We press on---Lynn the crate :|
 
Gary, if your "combustion monitor" is electronic, it will make no difference at all. The box looks like a near open circuit to the thermocouple, so no effect from + or - a little resistance.

If it is an electromechanical meter movement, however, it could make a noticeable difference. If the meter itself is 30 ohm, the external resistance required is 8 ohms, and the leads are shortened to 4 ohms, the readings from ambient will be (30+8)/(30+4) = about 12% above calibration. That might be close enough for most since peak is peak anyway. But actual values of the readings will be high by say ~100+deg in the example.
ron
 
Thank you to all who have answered my question. I guess I'll just leave it and it will be close enough. I still remember Dan's method of getting the mixture right and I can always revert to it. As I try to put it back together, I'm sure I'll have lots more questions. I've stated that I am 100 yards from the factory and 100 feet from Weber's but Jerry Saether is really the only person who really knows about the 1413 models. Quite often, if I need a part it will be the same part that they used on the early 1419 models so I have been fortunate in that respect.
Thanks again!
Gary
 
Both the EGT and CHT probes are thermocouples. The length of the wires is unlikely to be a problem in an aircraft, but it is very important to use the right wire if you need to extend them, and that basically means buying extension leads specific to the type of thermocouple in the probes. The probe wires are color coded, so usually you can just get thermocouple extension leads in the same colors. Match them up, same color to same color. It IS possible to use copper wire as the extensions, but if you do, keep the two connections where the original leads connect to the copper extensions right next to each other (but electrically insulated), and wrap them together with a little foam tape to keep the two 'junctions' at the same temp. The meter readings will be off by up to 100 deg F, but it will be consistent, and the method of leaning to a point relative to the peak means you don't care.

On my 14-13-2 the lone CHT has a proper extension, but it is connected with a knife-edge connector, which just doesn't keep a good connection for the microvolt probe output. Soon as I find a round tuit, I'll put in a screw type connector. TC leads are not solderable, so you can only make mechanical connections to them...
 
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