Cylinder peaks way behind others

[Shadrach]

31 minutes ago, A64Pilot said:

That’s why I’d like to see an extended mag check, to see if there is a significant difference in egt between the two, mags can cross fire etc, but unlikely both are identical malfunctions, same for plug leads.

What I’m calling an extended mag check is on each mag long enough to see EGT’s stabilize.

If the two mags are close to the same EGT, that ought to eliminate the ignition system, plugs, mags, harness etc. I’ve even seen an ignition switch cause an intermittent miss, that took awhile to find

I agree. I’d also like to know the raw EGT number from full rich to peak EGT. It might be useful to know how rich of peak it’s running with the mixtures balls to the wall.  
 

I think it’s good practice to do methodical in flight mag checks on a regular basis. I usually check each cylinder individually. Takes about a minute from start to finish.

[Shadrach]

1 hour ago, Fly Boomer said:

I have suggested plug, wire, or mag, but he says in-flight mag check is perfect.

I guess that means we need to define perfect… just running smoothly is a pretty low bar.
 

I wonder what his mixture setting is during the in flight check? Is #4 crossing into 1700° territory during a best power mag check? Will it run smoothly on one mag at 25° LOP? 

[Fly Boomer]

4 minutes ago, Shadrach said:

Will it run smoothly on one mag at 25° LOP? 

If there be gremlins, that will probably find them.

[vik]

On 4/26/2023 at 9:29 PM, lithium366 said:

Here is a picture if a #4 valves.

What about the pictures of exhaust valves #1,2 and 3? The carbon deposits on #4 exhaust look suspicious. No obvious sign of one side overheating/burn thru, but not a complete circle as well.

On the other hand, a problem with the valve would show up on the leakdown test. It might also worth to do a valve guide test for (partially) stuck valve following Lycoming SB.

Edited April 28, 2023 by vik
fix typo

[A64Pilot]

I’d be tempted to screw in an automobile compression tester and spin it over, throttle fully open and see what the compression is, compared to another cylinder.

[jordanjms]

@lithium366, did you ever get a resolution to this? I'm having the exact same issue. Savvy suggests checking the dry tappet clearance like you mentioned. Did you try that?

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[lithium366]

15 minutes ago, jordanjms said:

@lithium366, did you ever get a resolution to this? I'm having the exact same issue. Savvy suggests checking the dry tappet clearance like you mentioned. Did you try that?

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I did and found an excessive clearance on #4 intake that is likely a contribution. That said it is not terribly bad and I did not dig further yet in that direction.

That said, I also uploaded another flight and they said to look for an induction leak, which I did and found nothing but replaced intake gaskets anyways

Let us know when you find out what’s your issue!

Edited August 18, 2023 by lithium366

[jordanjms]

Did you fix the tappet clearance and did that improve the GAMI spread and high EGT or did that get solved with the replacement of the intake gasket?

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[lithium366]

6 minutes ago, jordanjms said:

Did you fix the tappet clearance and did that improve the GAMI spread and high EGT or did that get solved with the replacement of the intake gasket?

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I tried longer push rod - did not help and probably should not if timing is affected because of a cam lobe shape change.  Issue is not fixed yet

Edited August 18, 2023 by lithium366