Fitting egt probes on Rotax 912

[FELX]

The D120 manual says that the egt probes should be fitted to the exhausts of the two rear cylinders. The rear cylinder exhaust pipes on my Rotax 912 are relatively short and curved for almost all of their length - not a good fitting position.

On the other hand the front cylinders have long straight sections which are ideal for fitting the probes and clips.

Can anyone advise on the balance of a better fit (front cylinders) v. the 'correct' positioning where the pipe is going to be curved????

Many thanks.

Terry.

 

[PilotKris]

While we're at it, why only 2 EGT probes?

While I know that there are only two carbs, one for each cylinder bank, and theoretically the two cylinders on the bank should be seeing the same mixture, that's not what happens in the real world. Possible reasons for different EGTs on the same bank include:

Intake leak
Fouled plugs
Ignition problems
Stuck valves
Exhaust leaks
Carb problems

Even though we can't control the mixture, having EGT data on 4 cylinders is MORE than twice as valuable as having it only on 2.

PilotKris

 

[dynonsupport]

After consulting with the Rotax gurus over at Lockwood Aviation (and they in turn consulted with Rotax technical support), we learned that of all the things one can glean from EGTs, the one that is most useful on the 912 is the ability to detect carbs out of sync. This requires only one EGT per bank. Additionally, on the 912, you can often see quite very different EGTs between the front and the rear pairs - as much as a few hundred degrees. This is inherent in the operation of the engine, and Rotax has seen people confused by the behavior when all four are monitored. In fact, measuring EGT isn't a requirement on the 912 per Rotax spec.

All of that said, you can certainly opt to add 2 more runs of EGT wire (type K thermocouple wire) to the harness and purchase two more Rotax EGTs if you'd like to add them. As you pointed out, there is more information that can be gained by monitoring all four if you know what you're looking for.

 

[PilotKris]

Typical... Rotax "Dumbing" it up 'cause they think we "Stupid-Pilots" couldn't possibly understand the concepts.