First engine issue in flight

[haymak3r]

Hey everybody. I am super curious what everybody's thoughts are on this, as we are a bit stumped.

So, yesterday I flew from my home base to where my mechanic is about 10 minutes away. The flight was great, as was my flight the day before. Engine run-up was great, about 50 rpm drop equally across both mags. I was flying there to replace my cht sensor as my cht gauge has been fluctuating off the bottom to the head temp off and on for about a month now. It doesn't always happen, but we felt that replacing the original sensor wouldn't be a bad idea.

After we put the new one in, I had planned on going on a longer flight. I pulled to the runup area, and performed a normal runup. There was no discernable difference between mags, and no missing or anything. Everything was normal. My takeoff was fine, and as I climbed out I noticed that I was starting to get a vibration, almost like my prop was out of balance. I know it needs balanced. At 2100-2300 rpms I get a bit of vibration. Just slight. And have since I got the plane. Anyways, adjusting prop pitch made no difference. I adjusted mixture, power, changed tanks, turned the electric fuel pump on just in case something fuel related was impacting things. I did notice that after I cleaned up, my speed wasn't raising to 120 for a cruise climb. I checked mags, and it seemed that my left mag made things worse. I immediately turned around, and told approach I was coming back to the field.

 

When I got back, I explained everything to my mechanic. He had me go and do a higher rpm runup to try and reproduce the issue. I started by going to 2000 rpm, and checked the left mag, I instantly had a miss and the engine backfired. Right side was smooth. Back to the left, and same thing.

Put it back in the shop, and pulled the cowling off to start checking things. OH, and the cht gauge basically started doing the same thing right after taking off. Well when we pulled the lower cowling, the cht sensor wire, and post were just hanging in the air. The plastic had completely melted away from it????? We then pulled spark plugs, and found that cyl 1 (where the cht sensor screws in to) were completely bad from what looks like burned on oil or lead? Just to also give you a heads up, My annual was last month, and there was no difference between all 4 cylinders. All 8 plugs had a decent insulator color but we did find 2 with cracked insulators. We replaced them.

 

We then checked the mags and timing, and everything checked out there just in case. ran a compression check and it was 73/80... Checked inside with a boroscope. and the valves/piston/walls look perfectly normal Though there was just a slight amount of oil sitting on the bottom of the cylinder. We suspect that my valve guides may need to be replaced? I am attaching pics of the two plugs, and the sensor(original in the pic too). The worst one was on the bottom which is the left mag. you can see #2's top plug in the pic too. The other 6 look almost identical to that one. We also checked the fuel injector, and it looks completely fine.

 

Some additional information. I noticed my oil temps were slightly higher than normal. Usually the gauge sits right in the middle, but it went up to just below 3/4 of the way to the top of the green. The temp didn't seem to come down after landing really either nor did it during descent. Both not typical. We're waiting for 2 new spark plugs prior to doing any more testing, we plan on getting the engine to temp, and to 1. see if there is a failure noticed on the left mag, or 2. whether the cylinder get's super hot.. Outside of the cht temp issue, we see no other signs of that cylinder getting so hot that it would literally melt the sensor like that.

 

Sorry for the long story, but I wanted to give as much info as I could for the masses

Any thoughts/ideas would be greatly appreciated!

Sincerely,

Chris

 

[cbarry]

Are the fuel injectors clean and not clogged?

[haymak3r]

yep. completely clear. He is going to flow test? from the distribution valve today or tomorrow to make sure they are all even. Sorry if I used the wrong terms lol. I forgot to mention that I feel that the vibration I was feeling in the air was due to a cold cylinder now though. just need to determine if it got super hot (not sure how) and also why the plugs look so bad. 

[A64Pilot]

Only thing I can think of to get it that hot is detonation, hopefully you dodged a bullet cause the borescope looks good

Only thing I can think of to get you detonating on one cylinder is lean at real high power.’

I had a 210 that would clog injectors every now and again, first time it happened I went full rich and high boost, that made the other 5 slobbering rich. but didn’t hurt anything.

Second time it happened I pulled power back and leaned it out, that made the lean cylinder so lean it quit firing. I think that was safer than going slobbering rich on five to try to control the lean one. After the second time I carried tools and a can of carb cleaner, so of course it never clogged another injector.

I had a UBG-16 so it wasn’t hard to figure out what was happening.

But if there is no damage, you literally dodged a bullet if I diagnosed correctly, go buy a lottery ticket, but when things get weird remember at low power you can’t hurt the motor with mixture, so reduce to 65% or so and nothing bad can happen from a clogged injector, assuming of course you can maintain altitude.

The flow test is to verify injectors are operating correctly as in not blocked

Edited May 12, 2022 by A64Pilot

[carusoam]

Hay!

Got an engine monitor…?

We’re looking to have a discussion in the new arena…. 

1) You have oil on the inside where it doesn’t belong…. That is a really messy plug…

2) You have heat on the outside where it doesn’t belong… It isn’t normal to have a temp sensor melt away…

Post some data, post more pics….

Pp thoughts only, not a mechanic…

Best regards,

-a-

[anthonydesmet]

+1 for more engine data.  Hopefully the faulty CHT gauge isn’t your only source of CHT but if it is and let’s assume it was not faulty and it was trying to tell you something since it happened twice…..assume rapid CHT rise before it melted and bounced to zero …then the rapid rise may indicate detonation.  Also another way to be confident it’s not your mag would be to do an in flight mag check.  I had a mag go bad that checked fine on deck but when I got airborne and did an in flight check I had rapid CHT rise and EGT and lots of roughness…..I don’t think I would rule out the mag just yet.  More engine data will help isolate.

[PT20J]

Insulators on plugs shouldn’t crack in normal operation. Perhaps the two you found at annual were dropped during an earlier cleaning which can crack them. The insulator on the bad plug in your picture looks to be broken and perhaps you missed a crack in it during the annual inspection. A broken insulator can cause preignition which leads to detonation and high temps.  

[A64Pilot]

However the pretty classic calling card of detonation is a broken insulator. Pre-ignition isn’t the same as detonation of course but the outcome often is so similar as to not really matter. It differs in that pre-ignition is an early ignition, that has a normal flame spread just occurs before it should, and can lead to detonation, often the source of ignition is a hot spot, glowing bit of carbon or whatever, but could of course be from a damaged plug, I’ve not seen that but I’m not writing that off either. But I’m betting detonation broke the plug. Detonation breaks things, knocks holes in pistons etc.

Detonation is so destructive as it’s the sudden ignition of the entire fuel / air charge, there is no normal flame spread it’s literally an explosion, so pressures and temps go much higher than is normally possible, no matter you do with the mixture knob.

I’m hoping the oil in the cylinder was oil and maybe some fuel from a dead as in not firing cylinder that’s normally burnt off, but getting so hot as to melt the temp sending unit is a new one for me.

Cylinders, pistons often don’t survive detonation. Being as I don’t have to pay myself labor, I’d pull the jug and inspect the piston and cylinder

Edited May 13, 2022 by A64Pilot

[N201MKTurbo]

I noticed that you didn't check the mags in flight when you had the problem. That should be one of the first things you do. That's why we have mag switches, so you can turn one off if it starts to misbehave. It seems everybody is afraid to switch them in flight.

 

Edited May 13, 2022 by N201MKTurbo

[Rick Junkin]

17 minutes ago, N201MKTurbo said:

I noticed that you didn't check the mags in flight when you had the problem.

I think you missed this line in the original post.

16 hours ago, haymak3r said:

I checked mags, and it seemed that my left mag made things worse. I immediately turned around, and told approach I was coming back to the field.

Cheers,
Rick

[haymak3r]

16 hours ago, carusoam said:

Hay!

Got an engine monitor…?

We’re looking to have a discussion in the new arena…. 

1) You have oil on the inside where it doesn’t belong…. That is a really messy plug…

2) You have heat on the outside where it doesn’t belong… It isn’t normal to have a temp sensor melt away…

Post some data, post more pics….

Pp thoughts only, not a mechanic…

Best regards,

-a-

I dont have an engine monitor yet. The gi-275 eis is sitting in the shop though. We are waiting on the sensor kit currently.

 

only one cht which was on cyl 1. I will try to get more pics, and I was definitely full rich when this happened, and did drop power and did lean some with no noticeable difference. Went back to full rich and up to 25” map as i continued to troubleshoot. 
 

the cht gauge was just starting to move in to the green when it dropped to nothing and then bounced around presumeably when it had come apart and the wire was grounding on something as it flapped around.

[Ragsf15e]

29 minutes ago, haymak3r said:

I dont have an engine monitor yet. The gi-275 eis is sitting in the shop though. We are waiting on the sensor kit currently.

 

only one cht which was on cyl 1. I will try to get more pics, and I was definitely full rich when this happened, and did drop power and did lean some with no noticeable difference. Went back to full rich and up to 25” map as i continued to troubleshoot. 
 

the cht gauge was just starting to move in to the green when it dropped to nothing and then bounced around presumeably when it had come apart and the wire was grounding on something as it flapped around.

Nice job making a good decision and getting her back on the ground safely.  While it may seem an easy decision looking back, it's easy to have a "helmet fire" at that point and mess something else up (gear up, super fast final, no clearance to land, etc).  Glad you get to calmly sort out the problem with your mechanic.

[Bolter]

I had some cracked spark plugs (in a J) like you are showing.  The best I could tell, including that I ran for hundreds of hours after the replacement, the plugs cracked from their own weakness.  It was not the result of poor engine management or detonation or pre-ignition.  With the cracked plugs, the engine ran rough during runup, especially when turning off the mag that had the cracked plug, that I scrubbed the flight.

I may not have read the OP correctly, but was the engine running smoothly after the cracked plugs were replaced?  With my case, that solved everything, and best I could tell, it was a few bad plugs.  They were relatively new plugs at the time, and it never happened again when I replaced all with new fat electrode Tempests.

Just a data point of a similar experience.

-dan

[N201MKTurbo]

3 hours ago, Junkman said:

I think you missed this line in the original post.

Cheers,
Rick

my bad...

[haymak3r]

We are still waiting on plugs. They will be here Monday. And yes. I checked gear down like 5 times lol. The adrenaline was there and so was fighting that for sure. Just went over the checklists and relied on my training to keep as calm as possible. 
 

Honestly, the one take away from the onset of this is my lack of action. At first when I noticed the vibration I sat there a couple seconds before it sunk in that something wasn’t right. It seemed like an eternity, but I was no more than just leaving the pattern before I started really troubleshooting. I should have instantly turned back but minus the cht gauge everything was in the green. Lack of experience I think played a role there. 

[PT20J]

7 hours ago, haymak3r said:

I dont have an engine monitor yet. The gi-275 eis is sitting in the shop though. We are waiting on the sensor kit currently.

 

only one cht which was on cyl 1. I will try to get more pics, and I was definitely full rich when this happened, and did drop power and did lean some with no noticeable difference. Went back to full rich and up to 25” map as i continued to troubleshoot. 
 

the cht gauge was just starting to move in to the green when it dropped to nothing and then bounced around presumeably when it had come apart and the wire was grounding on something as it flapped around.

A few interesting points from your description.

1) I'm pretty sure that all the M20Js are supposed to have the factory CHT probe on cylinder #3 (right rear viewed from cockpit), not cylinder #1.

2) You never saw the CHT with the new probe get very high before the probe apparently failed.

3) If the cylinder head got hot enough to damage the CHT probe, I would expect to see melting of the piston crown at the edges and damage to both spark plugs. The CHT probe is not at the hottest part of the cylinder head.

4) You adjusted all the engine controls and the engine was still rough. If it were detonation it would have stopped when you reduced power. 

5) From your testing in the air and on the ground, the roughness seems clearly caused by the bad plug.

From the evidence, I don't think there was detonation. The roughness was likely caused by the bad plug. It's not clear why the CHT probe failed. 

I would check all the obvious things: injectors, timing, plugs. I'd put a new CHT probe on #3 and run it up until all the temps are in the green and if that goes well then test fly it.

Skip

 

[haymak3r]

That is the current plan.

[Ragsf15e]

9 hours ago, haymak3r said:

We are still waiting on plugs. They will be here Monday. And yes. I checked gear down like 5 times lol. The adrenaline was there and so was fighting that for sure. Just went over the checklists and relied on my training to keep as calm as possible. 
 

Honestly, the one take away from the onset of this is my lack of action. At first when I noticed the vibration I sat there a couple seconds before it sunk in that something wasn’t right. It seemed like an eternity, but I was no more than just leaving the pattern before I started really troubleshooting. I should have instantly turned back but minus the cht gauge everything was in the green. Lack of experience I think played a role there. 

That’s pretty much how it goes for all of us.  There’s a short denial period for everyone.

[Hank]

8 minutes ago, Ragsf15e said:

That’s pretty much how it goes for all of us.  There’s a short denial period for everyone.

A little denial. A little What's going on? An attempt or two to "fix" what might be wrong mixed with some confirmations that it really isn't right.

My deal last summer was on morning departure to meet my wife's extended family at the beach. Runup was good, takeoff was long (oops! Loaded heavy and forgot to add flaps), climb was only 400 fpm. Took about two or tnree minutes, including discussion with my wife, to turn back and land. After an hours' work in tha hangar with no improvement to 250-300 RPM drop on the left mag, threw in the towel and drove home.

You did good diverting and landing. We both lived to fly another day. Hope your issue isnt too bad, mine was a bad lead on my year-old Kelly ignition harness . . . .

[haymak3r]

Agreed. I hope it is a faulty sensor plus the cracked and barely working plugs. Will just monitor the piss out of it. Also as suggested will look in to why the sensor was even on cyl 1. I am sure it has been there for years… my sensor kit will be here in a couple days and will then have sensors everywhere

 

 

[PT20J]

Many years ago I was at the Reno Air Races when Bob Hoover had an engine problem in the P-51 and ended up with oil gushing all over the airplane. I had a VHF radio and was listening to the tower frequency and heard him call Mayday. His voice was higher and he didn't sound all that calm (He by no means sounded panicked, but he didn't sound like the, "Ah, Houston we've had a problem" test pilot understatement either). No one is immune.

Skip

[haymak3r]

Just wanted to follow up, that we put 2 new spark plugs in, and put a used cht that my mechanic had in to cyl3 per the manual. I've flown 4 times now and checked the plugs after each time. 

1. the cht temp sensor is working as expected. I temps seem to be right where they used to be, and all is well with that. Pawning off the melted new one as a bad part.

2. the plugs look great! they are dry, and the insulator shows just slightly brown which I feel is exactly where they should be, and are inline with how the others had looked like when the issue first started.

I flew a longer flight over the cascades this last weekend, and everything checked out just fine. Hopefully I don't see any issues like this again.

[PT20J]

Thanks for the followup.