Deposit on top of cylinder

[Aiki_Aviator]

Today I decided to re-gap my plugs and curiously looked inside my cylinders to see what I could see.

I have only run 50 hrs on the engine and 35 flight hrs. The difference being obviously taxi time, preflight testing, and a very annoying RPM issue.

Now while I was poking about, I noticed a deposit on the top of the cylinder near the spark plug on two cylinders.

Photo below:



I guess I am wanting some feedback from people on this issue and is it worth getting concerned about or is it standard and completely normal.

NOTE: I have not flown this very hard and it has been quite RICH to date, however, looking at getting into some significant flights soon and more lean mixture is to follow.

Thanks in advance.

[terrykohler]

...Especially if you don't lean agressively when you're on the ground, and only marginally in the air. Pull one or two of your lower plugs- you're likely starting to foul them as well. Good news- it's an easy fix.
Terry, CFI
RV9A N323TP

[Aiki_Aviator]

Sorry, just to clarify, the fix is to aggressively lean? Will that effectively burn that deposit off?

[newt]

At the power level you run at for taxiing, you can do whatever you like with the red knob without cooking anything.

The accepted technique for ground leaning is to set 1000 rpm and wind back the mixture until the revs increase a bit, then keep leaning until they JUST start to decrease.

That puts the mixture at a maximally lean position; and also means your engine will splutter and cough and probably stop if you forget to enrich before takeoff.

On my O-320, there's only 1 turn of the vernier between that point and the engine stopping altogether, so I have to approach the peak very slowly, to make sure I don't overshoot, which makes the process more time consuming than I'm typically prepared to accept when I've just vacated a runway and I'm concentrating on taxiing to the hangar. So I ground-lean by pulling the red knob all the way out then pushing it in about 1/8" before the engine starts to run down. Achieves approximately the same result. The important thing for safety is that the engine should stop if you attempt high power.

- mark

[N427EF]

All engines will accumulate such carbon deposits over time, some more some less.
Maximum leaning as described in the above post will somewhat minimize such deposits.
The only tiime you will see a really clean cylinder and piston is after detonation occurred (mild detonation).
These carbon deposits will accumulate and occasionally pieces of it will break off and make their way out the exhaust pipe.

Paul describes the perfect leaning procedure, it is exactly what I do, at least the part on the ground