Severe carbon buildup in cylinder 1 Rotax 912 S3 before the 100-hour inspection, here!…
The mechanic examined the engine’s spark plugs and observed that the spark plug of cylinder 1 (front right) was extremely fouled. This prompted him to use borescope camera to inspect the cylinder, where he also observed contamination.
Upon opening cylinder 1, it was noted that there was carbon build-up on the valves and the piston head. The exhaust valve and the channel behind it were dry (no oil).
The drained oil from the system (100 hours) was very dark and smelled burnt (like smoky BBQ sauce!). Discolorations on the inner wall of the cylinder were visible, indicating possible overheating.
Cylinder 1 was replaced in October last year after previous damage (same issue) and has accumulated only 99:30 flight hours!
Various potential causes were discussed and examined without a clearly identifiable cause.
This engine has an improvement of the original exhaust system for AT01 with a Rotax 912S3 engine installed.
Something is going on with these Rotax engines. Anybody out there with same issues?
01cylinder_pdf
[ @PilotKarinaNVFR new thread started ]
PilotKarinaNVFR wrote:
Something is going on with these Rotax engines. Anybody out there with same issues?
Run them and maintain them according to the Rotax manual, and they will be fine IMO.
PilotKarinaNVFR wrote:
Cylinder 1 was replaced in October last year after previous damage (same issue)
What exactly was replaced? only the cylinder? not the top or the piston or rings?
PilotKarinaNVFR wrote:
Severe carbon buildup in cylinder 1 Rotax 912 S3 before the 100-hour inspection, here!…
What fuel was used?
I would also ask what oil?
I don’t remember ever hearing about carbon build up before on a Rotax. What causes carbon build up in general? It obviously must be something wrong with the combustion, or it starts burning oil? Does burning oil cause carbon buildup? perhaps. Running the engine too cold is not a good thing, and idling below 2000 rpm is not good either (Rotax warns about that, sooting down the spark plugs). Apparently, in this case, it happens for one cylinder only though. Valves? ignition? carbs out of synch? rings?
I mentioned the oil because the POH for the Super Guépard advises the use of motorcycle type oil as well as UL95 car fuel.
Rotax are running a series of seminars and maintenance workshops around France.
One was held at one of the maintenance shops here at Fontenay le Comte LFFK.
Afterwards there.was much general discussion and this was one of the things that came up alongside more frequent oil changes if 100LL is used often and watching out for carbon or lead castellations (castle like deposits of carbon or lead) which eventually start to smoulder and burn leading to detonation at the wrong time and causing damage.
I admit to not understanding the full detail as the conversation deteriorated into math formulas and they tend to pass straight over my head.
The SG ULM does not have a manual mix control so there is no way for the pilot to change the mix setting other than messing with the carb on the ground.
If this carbon build-up is only present in one cylinder and occurs for the second time in a row, there’s obviously something wrong with combustion in that cylinder. Am I right to assume both the cylinder and the cylinder head assembly were replaced? If so, I would start the diagnostics from the ignition system.
