Aft cylinders vs forward cylinders (spark plug condition)

[hawgdrvr]

Just completed my first condition inspection and one thing I wanted to do as the engine is near 100 hours is change the plugs. I typically use lean assist to run LOP but initially there was probably some full rich time including learning to lean while taxiing in the beginning and during break-in. It was interesting to see the aft cylinder plugs were black, the forward cylinder plugs were clean. Why the difference?

Lycoming 363i - FX-3

[40m]

Just completed my first condition inspection and one thing I wanted to do as the engine is near 100 hours is change the plugs. I typically use lean assist to run LOP but initially there was probably some full rich time including learning to lean while taxiing in the beginning and during break-in. It was interesting to see the aft cylinder plugs were black, the forward cylinder plugs were clean. Why the difference?

Lycoming 363i - FX-3

Neal, because curious mind would like to know posting this on the SC Forum might be also be helpful.

[hawgdrvr]

Neal, because curious mind would like to know posting this on the SC Forum might be also be helpful.

I agree that would help too but my goal in posting here is to also get other CC aircraft owners to post here so we can share and learn from each other as well as to get CC to participate in the info share and learning.

[aeroaddict]

Congrats on the first 100hrs and your condition inspection.

In regard to the plugs:

aft plugs were 'black' as in shootie, threads looked wet, .....?

front plugs looked clean; brown, tan, gray, threads were dry shiny, .....?

Any 'clinkers' in any of the plugs?

Can you post a couple of pics of a typical black and clean plug?

[hawgdrvr]

Good idea, when I get back to the hangar to unpack and clean today or tomorrow I'll definitely post pictures as that is much more telling. Everything ran and runs great, just curious why the difference on aft cylinders vs. front cylinders in regards to the tips of the plugs. Pictures coming in a day or two...

[hawgdrvr]

Here is a picture. Left is aft cylinder(s) and right is forward. Also interesting is how dark it is up the threads on some plugs.

plugs.jpg

[Andy]

Here is a picture. Left is aft cylinder(s) and right is forward. Also interesting is how dark it is up the threads on some plugs.

That left plug was running very cold shortly before the engine was last shut down. Doesn't necessarily tell you anything about the temperature or mixture in cruise flight.

What was the fight profile immediately before the plugs were removed? If you don't know then review the data log and plot EGT, CHT, percent power, and fuel flow.

If you think the rear cylinders are running rich then run the GAMI spread test.

[hawgdrvr]

I flew one hour to the condition inspection location, 24 squared, LOP.

[Andy]

I flew one hour to the condition inspection location, 24 squared, LOP.

Ok, but how long on the ground before you shut down? Does the data log for that flight show cylinders 3 and 4 were running much colder than 1 and 2?

[hawgdrvr]

Ground time was short, guessing 5 minutes. Just curious why all plugs don't look the same.

It will be interesting to see the plugs after the next 100 hours as this first cycle consisted of break-in AND my learning to lean, lean while taxiing, etc. I learned during this condition inspection about leaning at shutdown watching the RPM rise approx 50 RPM before quitting. That gives me a better feel of leaning better while taxiing such as lean until the RPM starts to rise as a reference point.