Rough running engine

[Davo]

A friend recently purchased a Mooney M20J with an IO 360 A3B6D with approximately 600 hours on the engine since major overhaul through a respected engine shop. Logs are pretty complete all done through a Mooney service center in Florida since new. The only thing I don't see anywhere is the 500 hour service to the mags. The elevator controls were really stiff but, through great feedback, we resolved that easily with proper lubrication and cleaning. Anyway, he purchased it about 2 weeks ago and flew it to Northern California form the Phoenix area feeling it ran well. He wanted me to fly it last weekend. It felt rather rough on start up but run-up felt smoother with mag drop WNL. Applied power and I thought this was accelerating kind of slow. I passed this off as being used to my -9A. Climb out was dogged to say the least climbing at 400 fpm at 85 kts from an airport 160 feet MSL. I immediately returned to the airport thinking this wasn't right. My friend is an A&P and as a favor, started to look things over with me. We checked plug wires then plugs. All good except for #1 which had a pretty good soaking of oil top and bottom. Compression was 0 on #1 but 78 on the others. Staked the valve with no improvement. Definitely heard the hiss of air through the exhaust so, naturally, we thought the exhaust is valve stuck open. Borescope showed good movement and minimal crud on the seat. Cylinder walls looks perfect. We lapped the valve and checked valve guides. Compression came right up to 78/80 so we thought we're home free. Nope! started her up and still runs really rough. #1 is notably much cooler to the touch than all the others. (The insight CHT/EGT gauge is inop). Checked fuel flow at the injectors and is even all the way around. Restrictors are clean. Starts well but runs very rough. Swapped plugs around but the problem stayed with #1 cylinder.
So, I've got compression, fuel and air and the only thing I can think of that's left is spark. It's not the plugs since the rotation changed nothing. This has the dual (2in 1) magneto we all love so much but the mag drop on a run up is about 75 RPM. My A&P friend only works on airline jets for the past 25 years and he's stumped as well. I'm at the limit of my skillset and this is a certified plane so I can't really go any further, nor would I. He's going to try to find one of the local A&Ps that work on the field. I would really like to understand what could be the problem. I don't know how much resistance the plug wires should have but measures at 70.5 ohms. Any ideas?

Edited March 7, 2022 by Davo

[mike_elliott]

how tight is your intake system?

[PT20J]

If you get good run ups on both L and R it shouldn’t be the mag. I would further investigate the exhaust valve. Lapping will fix one that is just beginning not to seal well but doesn’t help with sticking which requires reaming the guide. 

[Guest]

Good compression does not mean good horsepower.  Pull the rocker covers and compare valve lift on several cylinders, a worn cam lobe can cause lack of power.

Clarence

[Davo]

32 minutes ago, M20Doc said:

Good compression does not mean good horsepower.  Pull the rocker covers and compare valve lift on several cylinders, a worn cam lobe can cause lack of power.

Clarence

Good idea. Thanks!

[Davo]

Update on the rough running. Put a dial indicator to compare lift on the cylinders with good compression with the #1. No difference. We reamed the valve guide and tested compression. Back to 78/80. Ran the engine and started smooth, turned rough after about a minute. RE-checked compression and back down. I've since pulled #1 and sent it off to Zephyrhills aircraft engines. I've known the previous owner (Charlie Meloit) and the new owner LJ Warren since early 2000's and they did fantastic work on a Trinidad I had. Honest and very fair, not to mention meticulous work. I gave LJ the story so far. I'll report his findings. I know when I 'm at my limit and need help. 

[Davo]

On 3/7/2022 at 7:36 AM, mike_elliott said:

how tight is your intake system?

Checked intake system. It's tight. Tried several methods and all checked fine.

[A64Pilot]

On 3/22/2022 at 10:21 AM, Davo said:

Update on the rough running. Put a dial indicator to compare lift on the cylinders with good compression with the #1. No difference. We reamed the valve guide and tested compression. Back to 78/80. Ran the engine and started smooth, turned rough after about a minute. RE-checked compression and back down. I've since pulled #1 and sent it off to Zephyrhills aircraft engines. I've known the previous owner (Charlie Meloit) and the new owner LJ Warren since early 2000's and they did fantastic work on a Trinidad I had. Honest and very fair, not to mention meticulous work. I gave LJ the story so far. I'll report his findings. I know when I 'm at my limit and need help. 

Something is goofy with that cylinder, you did the right thing and I’d bet lunch when you put the cylinder back on, it will be a different engine.

Just be sure to torque the opposite end of the studs too, meaning torque both ends of the studs is what I’m saying, not just the one side

[Davo]

Result of inspection by Zephyrhills Aircraft engines is the valve stem was "on the way to a complete failure of the exhaust valve"

LJ made mention that, on the Mooneys, the #4 cylinder is the most prone for issues such as this. Does anyone have more on this? Looking through the last annual, they made note that #4 was staked then had good compression, still does. Should I send #4 away or follow closely?

[carusoam]

There are a few tests for valve health…

and some maintenance procedures…

 

Valve health in a Lycoming… can be affected by the oil passage in the valve guides…

If the valve guide is full of carbon chunks, slowly turning into tube shaped diamonds, oil isn’t getting by like it needs to…

If your JPI’s EGTs are showing nicely jagged EGT patterns….. this is called sawtooth… a sign of sticky valves…

 

cleaning the valve guide… often a reaming exercise… is a good step….

The wobble test… is often a check for the wear that was caused by the lack of oil…

The rope trick… has something to do with this as well…

 

Got any engine monitor data to share?

Valves don’t usually fail without some warning…

Like morning sickness…

 

I don’t recall #4 being more susceptible than any others…  any EGTs and corresponding CHTs stand out on the engine monitor?  
 

#4 is in the back row… if it is overheating… expect that there are seals and airflow guides that may need attention….

 

What made LJ go looking for this?

Some get sticky valves…

My O360 got a stuck valve…

One is much worse than the others…

Both aren’t any good…

PP thoughts only, not a mechanic…

-a-

[jaylw314]

A cracked valve stem still wouldn't explain the rough running or the cool #1 cylinder, though, would it?

[Davo]

I have been really busy and haven't had time to post the result of this work. After top end work as noted above, the engine is smooooooth! Did a few ground runs as recommended by Zepherhills Aircraft engines and waiting on CHT probes before flying so we can monitor each cylinder.  

[Shadrach]

 

On 4/8/2022 at 3:47 PM, Davo said:

Result of inspection by Zephyrhills Aircraft engines is the valve stem was "on the way to a complete failure of the exhaust valve"

LJ made mention that, on the Mooneys, the #4 cylinder is the most prone for issues such as this. Does anyone have more on this? Looking through the last annual, they made note that #4 was staked then had good compression, still does. Should I send #4 away or follow closely?

In my experience #3 is the cylinder most prone to problems in most O/IO360 applications, not just Mooneys. It is possible with the oil cooler mounted above #4 that cylinder that problems could be more common  on J models. Given that #1 was your problem cylinder, I’m inclined to believe that this was an installation/manufacturing issue. Were these overhauled or new Lycoming cylinders at overhaul? I wouldn’t pull #4 just for the sake of pulling it. The question I’d be asking is what are the chances that the other three cylinders have sloppy valve specs. Perhaps it might be prudent to “rope trick” the other three cylinders and inspect the valve stems. It’s interesting to me that the guide was reamed but the condition of the valve stems poor condition was only noted after pulling the cylinder.  I’m not an expert on visual valve inspection but the valve in the picture does not look healthy to me.