I'm running this through my mechanic and also a subscription service that helps with these sorts of matters, but I'd sure like to hear what you guys think. I'm no mechanic, and I've only been an aircraft owner for a couple of years so I'm grasping at some correlations here.

Every once in a while I would get a bit of engine roughness and an increase in EGT on my single point EGT gauge. It would often happen early in a flight, on climb or initial cruise. I would enrichen the mixture, later adding a wing rock to the mix, the roughness would go away and EGT would come back down. It never happened frequently, but the worst was when it happened 5 times on a prolonged high powered climb a few months ago. Long story short, I've been chasing this for a while. The increase in EGT combined with roughness led me to believe that faulty fuel tank venting was causing a bit of starvation.

It just happened again for the first time in a while, and it just so happens I now have an engine monitor so I was able to get better info.

Here is what happened:

1. Departed KSMN at around noon, ambient was ~50*F, just me and half fuel
2. Climbed to 6,500, cruised at WOT or about 21", 2450rpm, leaned to 45* ROP, ~40* ambient
3. About 15 minutes later, I felt the same roughness I've felt before, it was subtle but my butt is hypersensitive to it
4. I rocked the wings, which is a measure I've taken the past, I'm unsure if that does any good, but I do it anyways. I notice that fuel flow HAS NOT dropped, which I find interesting. There are momentary increases in fuel fuel as I rock the wings.
5. I enrichen mixture, engine roughness starts to go away after a moment
6. I notice that EGT and CHT on cylinder 1 (which was the only data I had before the new engine monitor) increased, but stayed higher than all the rest of the cylinders regardless of mixture. Had to partially open cowl flaps to keep CHT on #1 below 380.
7. Continue to cruise, EGT on #1 spikes a couple of more times with subtle roughness, then levels out, again still higher than the rest.
8. Had to run the engine 1-1.5 GPH higher than normal to keep temps on #1 in line
9. As I descend into the KTWF area, MP increases, EGT on the other cylinders comes up closer to #1, #1 remains high.

I'm starting to wonder if it's actually an issue with cylinder #1. I checked the log book, compression on that cylinder for the last couple of annuals has been about average. That cylinder has not been apart since the engine was installed.

The data from the flight is big, and weirdly the file is formatted with a gap between each line so it takes some work to run charts from it. I will work on that. Seeing all the data will help provide more detail and clarity.

What do you think?

Stop rocking the wings, that is most likely just confusing the issue. Do a mag check in flight at 2400 rpm. You can have a plug that is good on run up go bad at higher RPM. I suspect your issue is an intake leak. Make sure your intake boots are all in good shape and clamps are tight. Which cylinder hits peak EGT first? I that the one you are setting you ROP by?
DENNY

I have a CGR-30p and can run the data file through the free Savvy analysis tool. I don’t think it required any data manipulation to make it work.

As said above; upload your data to the free savvy analysis tool. It should produce a clear and intuitive data set that you can share.

To me it sounds like either ignition or a failing exhaust valve. Could be induction leak but I’d think that would not be intermittent. The data will tell the story.

What does the egt on the cylinder in question do on a cold start; from startup up to operating temp?

I'm a total dummy, I thought you had to send it in for them to analyze it, I didn't realize there was a tool on the dashboard to run the trends. I just did that, here is what it shows, you can see the event at about 37 minutes:

I'm a big fan of the Savvy service. I put an engine monitor in a year ago and signed up for their QA package. The info I've gleaned from the monitor and their advice has given me great peace of mind running an O-470 that's 2100 SMOH.

Which brings me to your post. I can't help you with the event at 37 minutes, but I'd also ask them and/or your A&P about your #5 (green line). That low, fluctuating EGT on start coupled with the low CHT looks similar to a sticky exhaust valve that I had. I don't think I would have caught that as quickly without the engine monitor, and it would have been way harder to narrow down once I did realize it.

Great catch, looks I have two problematic cylinders.

Savvy got back to me on my ticket this morning, he asked me to do a lean test and inflight mag check which I'll do tonight and go from there. I'll keep you guys aprised of the results. I like to be sure and keep these threads alive to resolution so they're a good resource for folks later on searching for these sorts of things on the forum.

I don't think cylinder one has an issue, per se. Good catch by slowmover on Cylinder 5.

I don't think you mentioned what kind of engine this is - fuel injection or carb? If injection, what sort?

Something interesting is happening about 18 minutes in, looking at the CHT it is obvious that your #1 cylinder has something different to the rest. It gets colder while the rest are still getting hotter for several minutes.

At 37 minutes, it isn't so much overheating, it's coming back up to join the pack.

Perhaps cylinder 1 is the only cylinder running lean of peak - hence the flow test would help.

So if it's running lean, then suddenly getting hotter, that means the fuel flow is increasing and we see this on the trends. All cylinders get hotter, but number 1 gets a lot hotter. So it is probably going to peak EGT. We see this on the trends, the cylinder appears to be at the peak, although we cannot know until the flow test is performed. Do that test at 50% power.

So we know the cause of the issue is not in the lone cylinder, it's affecting all the cylinders. Why does it get richer? Stuffed fuel servo / carb not distributing the fuel evenly.

The alternatives would be airflow is decreasing, or the timing is too early. Could even be pre-ignition if you have lead hotspots or a hot plug.
You aren't leaning the engine when it's running above 75% power output, right? Or leaning to 40* ROP at cruise power above 65%? That might explain damage to cylinder 5, but there are all sorts of reasons for a sticky exhaust valve, overheating is only one. I think it's worth considering, but that is not the whole story.

Overall, I think the fuel controller is having a problem, all the trends point to those. It needs to be investigated.
Also, your fuel flows to each cylinder are not matched as cylinder 1 certainly appears to be running lean of peak when the rest are rich of peak in the cruise. Running this close to peak EGT will give you hot cylinders and can place a lot of stress on the engine, including the possibility of detonation. It may even explain the damage to cylinder 5.

Thanks for the insight!

This is a carburated O-470 in a 182. I have no idea how the engine was leaned prior to purchasing is two years ago, I've put about 250 hours on it, the engine has about 1200 at this point. That being said, I can't really be sure even of my own leaning techniques with the old single point engine monitor, I was running it richer than necessary most of the time. My airfield is at 4200ft so the airplane is rarely in a situation where it's producing more than 65% in cruise

At that moment, 37 minutes in, I enrichened the mixture as an instinctual response to the engine roughness

CParker wrote:At that moment, 37 minutes in, I enrichened the mixture as an instinctual response to the engine roughness

Yes I could see that in the trends. Sorry made one little edit above while you were replying, and it related to the carb option.

You'll want to run that engine a little richer, or run it a lot leaner, in my humble opinion.

Even at 4,200 ft, you will still get more than 65% power until you get to about 7000ft. You will get more than 75% until about 5000ft.

One more question, is you altitude changing any prior to the events? It does not take much to change for running fine to running too lean. DENNY

Altitude was steady at that point

Still waiting for a recommendation from Savvy, is there anything inherently different on the left and right sides of the engine on an O-470, or something that would explain why 2-4-6 run pretty tight but 1-3-5 are way more spread out? It's really noticeable when I isolate the sides on the graph.

CParker wrote:Altitude was steady at that point

Still waiting for a recommendation from Savvy, is there anything inherently different on the left and right sides of the engine on an O-470, or something that would explain why 2-4-6 run pretty tight but 1-3-5 are way more spread out? It's really noticeable when I isolate the sides on the graph.

It's not uncommon for some cylinders to consistently run hotter. Often the other air offtakes, direction of prop rotation, obstructions above the cylinders like an air intake, or similar will mean that one side of the engine gets better slightly airflow and cooling than the other. I am not familiar enough with your installation to comment specifically.

Savvy is saying an induction leak is the most likely cause. I'm not sure where the most likely place is to find an intermittent induction leak, but based on some interwebs searching it's not uncommon for the O-470 to have induction leaks. The right side of the engine, where I'm seeing the big differences in temps, is the side that had gaskets replaced and a new cylinder two years ago. I'm wondering if something is wonky from that work. Either way, next step is a pressure test, that's what I'll work towards and then update the group.

Thanks

I hope you get it fixed. Here's a recent flight on my O-470. Maybe it'll help you analyze yours better.

Well guys, looks like we finally found the issue. It shouldn't have been this hard to find, but it looks like switching IAs was the necessary change to find the root cause. There was a worn guide and subsequent sticking intake valve on #3. This was allowing exhaust gas to back into that side of the intake manifold and affect the cylinders on that side only, which is why they peaked first.

Trouble is, we found that my cam was beginning to have significant lobe wear and pitting, another issue that I'm baffled that my previous IA overlooked. Between the pitted cam and a couple of faulty cylinders it looks like I'm headed for an unexpected overhaul. Currently researching options but leaning towards Lycon with flow balanced cylinders. I'd love to go the XP470 route but a 206 is in my near future and I don't think it's money well spent at this point.

CParker wrote:.....we found that my cam was beginning to have significant lobe wear and pitting, another issue that I'm baffled that my previous IA overlooked.

Does your new IA have any thoughts on what caused the cam/lifter pitting? Any thoughts on how it should've been caught earlier?

Ross

pipeliner wrote:

CParker wrote:.....we found that my cam was beginning to have significant lobe wear and pitting, another issue that I'm baffled that my previous IA overlooked.

Does your new IA have any thoughts on what caused the cam/lifter pitting? Any thoughts on how it should've been caught earlier?

Ross

Yes I'm curious how this could have been caught earlier as well.

Delete. I didn’t read the thread first

I’m relatively new to aircraft ownership so anything I say should be cross referenced. That being said, my last oil analysis showed high iron but the previous IA dismissed the result without any action. Oil analysis is the best way as far as I can tell, if it’s bad enough the bits will show up in the oil filter as well but at that point you’re in trouble. This engine only had 1200 hours on it but was overhauled in ‘92 and sat (albeit in Arizona) for a few years.

The lesson I learned here is to make sure and push for analysis of any anomaly, don’t take “eh it’s probably nothing” for an answer. I’m glad I finally got a fresh set of eyes on the engine or I may have experienced a catastrophic failure at some point.

https://resources.savvyaviation.com/wp- ... stress.pdf