High EGT one cylinder

[Nev]

Yesterday I had an EGT suddenly go uncharacteristically hot on one cylinder, shortly after going LOP.

A mag check showed the right side to be running rough and missing on one. I put the mixture rich, changed power settings, leaned again, and it cleared after doing this a couple of times. I also remember it ran rough for 30 secs on startup, but not during the mag checks.

How do I tell if it's a spark plug issue, vs a valve with crud stuck under the seat issue ? Presumably because it ran rough on one mag I suspect maybe a plug issue.

Battson

[jaredyates]

Rotate the prop so that the cylinder in question has its intake valve open. Then you will be able to study the valve stem with your borescope. Seems like a dirty plug would self-indicate on visual inspection?

[Nev]

Thanks Jared. I'll pull the plugs and see if I can see the issue.

[Richard E]

Nev. It sounds similar to the problem that I had. Cyl 5 would rocket up as soon as I started leaning. It turned out to be a spark plug insulation failing, but only under compression. Run-ups were good. Idle OK and plugs looked good and clean.

We figured which magneto circuit it was by doing a left and right cut whilst in cruise. We then replaced both plugs (because we got them mixed up), but problem solved. I am having the two plugs tested under compression and await the result. But it now leans out easily with only a little bit of disparity on the EGTs.

You could try the cruise test to figure which plug and then get it tested or replace it.

[Nev]

Thanks Richard, sounds very similar.

[Battson]

If a mag check fixes the issue then it's definitely something in the ignition system, probably a plug - but worth keeping an open mind. The exhaust valve is unlikely to be a concern.
First thing I would do is change the relevant plug and see if it recurs.
It definitely sounds like a plug.

Edit: From memory, you are using auto plugs? Did you decide to change them every 100hrs, or run to failure?

[Nev]

I'm not at my first annual yet

[Battson]

zkelley2 - I guess you don't have the same thrust / weight / tire combination - as I am pretty sure we're all using the same brake pads....

[zkelley2]

Could be different calipers? How well your bleed on the brake system is?

[Nev]

I've got dual EMags (Very happy with them so far). But I'm only changing the spark plugs "on condition".

Today I removed the plugs from the cylinder in question and found a lot of lead in that lower plug. I gave all the lower plugs a clean - they needed it too, and I replaced the offending plug with a new one. Not sure if my logic pans out with that.

Incidentally, I'm not done one year yet, but 167 hours, so they're doing ok. Probably the main culprit contributing to the plug fouling is me operating in the circuit at full rich mixture ( 700 landings on the Bearhawk now). I no longer lean the mixture in the circuit, too labor intensive. At some point I'll get the hang of landing it, and the plugs will run lean and lead free from that point on .

[jaredyates]

Glad you found an explanation for the problem. It sounds like the plug in question was in a condition to be replaced.

[Nev]

Yep that's my thought too Jared. Always great to get the thoughts of people here - usually I end up learning something!

[Utah-Jay]

Lead…. I know it is a touchy subject on some forums, but I am really looking forward to the G100UL fuel. I do not want lead in my engine

[Nev]

Here's what it looked like on the engine data download. As soon as I leaned the fuel flow (upper blue line) the #4 EGT (purple line) went high. The second graph shows a mag check where the #4 EGT suddenly goes cold and drops off the chart.

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13E417CB-2E1D-40A9-95C6-38142DCAC762.jpg