Rough engine at idle on initial startup

[gtsio520]

Hello, for about a month now on the first start of the day with a cold engine, after a few minutes I get a vibration on my engine. Along with the vibration I get an EGT drop (90 degrees) on the number two cylinder. This lasts about five seconds and then goes back to normal. I have an IO360 A1A (500 SMOH) with Lycoming fuel injectors initially I thought it was an ignition problem, but when I tested my magneto‘s at 1000 RPM, the EGT’s would spike up on a single magneto. This is making me think it’s a fuel issue. I removed and cleaned the injector and it looked fine. I remove spark plugs and they as well look fin. When the engine is warm I have no issues. Mag drops or less than 50 at run-up. Any ideas?

[hammdo]

Lycoming morning sickness — may need the exhaust valve guide reamed…

Lycoming may have an SB on that…

https://www.aopa.org/news-and-media/all-news/2022/july/12/aircraft-maintenance-reaming-lapping-other-valve-tasks#:~:text=If the valve stem is,as Lycoming “morning sickness.”

found it…

https://www.lycoming.com/sites/default/files/attachments/Procedure%20to%20Determine%20Exhaust%20Value%20and%20Guide%20Condition.pdf

-Don

[ArtVandelay]

You can try adding MMO to your oil to clean the valve stems to see if it helps.

[Andy95W]

Don nailed it- your engine (#2 cylinder, specifically) is showing classic signs of an exhaust valve just starting to stick.  It won’t get better, Marvel Mystery Oil might help but doubtful.

The only real cure is to ream the exhaust valve guide IAW the Service Bulletin.  If it’s not done, it will get worse.  Eventually it will stick the valve so badly there’s a good chance it’ll bend the pushrod and the shroud.  At that point, you’ll need a cylinder overhaul.

The EGTs spiking on a single magneto is completely normal.  That happens because with only one spark plug firing, not all the fuel is burned in the cylinder.  Some of it is still burning during the exhaust stroke so the EGT probes show the increase.

[dzeleski]

As said already this is a fairly urgent situation. I would be flying to a shop that is willing to ream the valve guide without pulling a cylinder (using the rope trick) ASAP. The more you fly it the higher the risk goes.

An EGT spike on a single magneto is also completely normal and something those of us with an engine monitor actually look for as it means you have a healthy check.

I have also had cases after a long hot XC that a fuel line out of the spider is vapor locked more then the others and that cylinder takes a second to get fuel compared to the others. This feels different however because its only on initial start and then the cylinder comes online and stays online. In the case of a stuck valve it will come and go as the dissimilar metals expand at different rates and interfere randomly.

Edit: AirMods is near by to you (N87). That's who does my work and who did my valve guide reaming. Dave knows how to do the rope trick to keep this repair as non invasive as possible.

Here are a couple videos of my stuck valves that have occurred:

 

Edited November 30 by dzeleski

[DC_Brasil]

 

Great webinar from Mike Bush about valve sticking.

https://youtu.be/7ohsVvYbAaQ?si=nLwJ9cTg9ANzh3kE

[gtsio520]

Wow DC, after watching that I’ve been doing it all wrong. I never lean on the ground and my engine CHTs run low 300s. I’ll start running them higher and leaning on the ground. 

[jlunseth]

The engine should always be leaned on the ground and shortly after start-up. As you lean out at idle/taxi power, the RPMs will rise approximately 75 RPMs and then fall off. That is called "idle rise." Pull it out to peak idle rise and use that for all ground ops. If a turbo, put it in your "Before Takeoff" checklist to make the mixture full rich for takeoff, you don't want to take off with the mixture leaned with a turbo engine. I am not sure what you have, your signature line says it is an E (normally aspirated) but your user name suggests a turbo. In any event, leaning to idle rise should be done with both engine types.

In my checklist, I have a "Before Takeoff" section that includes putting the mixture to full rich, with a turbo I always takeoff full rich because regardless of airport altitude, the engine will always make 100%HP on takeoff. I always run my Before Takeoff list when at the hold short line. If a turbo, you should always check your engine monitor/EGT gauge as soon as you are off the ground to make sure you don't have spiking TIT, which means you forgot to put the mixture in full. Immediately fix it if you see that. But back to the original point, always lean to idle rise on the ground. I watched that Mike Busch video and he says he leans even more aggressively than just idle rise. Nothing inherently wrong with that, you should run the engine as lean as possible on the ground, but in my engine it is possible to lean too aggressively on the ground with the result that if you try to increase the power by putting in a little more MP, the engine will try to quit. Just an inconvenience on the ground, because you can restart. Maybe not a problem with your engine but it is possible with my TSIO360, which is why I generally don't lean past peak idle rise.