Dropped Cylinder

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dweyant

Pre-takeoff checklist
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Dan
Took the wife and daughter for a flight last night for dinner.

After dinner we went to fly home and I thought the engine sounded a bit off, but I couldn't quite put my finger on it.

However, when I did my runup I had a large RPM drop on the left magneto. Looking at my JPI it showed no EGT's on cylinder number three.

I aborted the flight and was fortunately able to borrow a crew car to drive home (made a much longer evening than I had intended).

So, what are the likely causes, and how difficult is it going to be to get this repaired? There is a mechanic on the field, but I'm going to call my mechanic and see if he has time to drive up and look at it with me.

Thanks for any suggestions.

-Dan
 
More than likely a fouled spark plug.

Did you lean it on the ground?

Has it done this before?

Have the mechanic on the field look at it first. More than likely it is simple.
 
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I did have it leaned for taxi. I also tried leaning it out until it ran rough to burn off anything.

I've had it run rough from fouled plugs before, but never totally lose a cylinder, does that make sense?

-Dan
 
dweyant said:
I did have it leaned for taxi. I also tried leaning it out until it ran rough to burn off anything.

I've had it run rough from fouled plugs before, but never totally lose a cylinder, does that make sense?

-Dan
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Makes perfect sense. :D

Gotta be a fouled plug. Good call getting a crew car. You would be surprised at how many "pilots" would have taken off and hoped the plug cleared. :eek:

Have the field mechanic clean the plugs, do a compression, and look for anything else obvious. It's always a good idea to let your mechanic know you have options and could use this other guy to do your future annuals. ;)
 
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Geico266 said:
Makes perfect sense. :D

Gotta be a fouled plug. Good call getting a crew car. You would be surprised at how many "pilots" would have taken off and hoped the plug cleared. :eek:

Have the field mechanic clean the plugs, do a compression, and look for anything else obvious. It's always a good idea to let your mechanic know you have options and could use this other guy to do your future annuals. ;)
Click to expand...

Thanks, I hope your right and that is all it is. I'll give them a call here in a bit when they open up.

-Dan
 
You have the data on what cylinder and what mag has the issue, that narrows it to one plug or wire...
 
Yup. I lean aggressively on the ground after flying a rental 172RG that fouled plugs all the time many years ago.

When the same happened to me a couple years ago, I knew it wasn't a fouled plug.

The plug wire had broken at the plug connection and had quite literally, fallen off.

New plug wire, it was back to normal.

And now you know why we do mag checks. Amongst other reasons. ;)
 
Just got a call back from the mechanic.

The plug was badly fouled. He cleaned it up and it is running fine, so that is good news.

Now my question is, how can I minimize/prevent this from happening in the future?

He also said the idle sounds just slightly off. Like some of the other plugs might have some fouling. Should I have my local mechanic clean all of them?

Thanks,

-Dan
 
lean the stink out of it.

if you lean it corectly on the ground you will never take off with the mixture still leaned, as the engine will die if you advance the throttle.
 
carry a plug wrench and clean it your self.

that is owner/operator maintenance (preventive maintenance)
 
dweyant said:
I did have it leaned for taxi. I also tried leaning it out until it ran rough to burn off anything.

I've had it run rough from fouled plugs before, but never totally lose a cylinder, does that make sense?

-Dan
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Sure if you were only on one mag when the cylinder dropped. Did you remember to switch both mags on when you ran it up to clear it?
 
dweyant said:
Now my question is, how can I minimize/prevent this from happening in the future?

He also said the idle sounds just slightly off. Like some of the other plugs might have some fouling. Should I have my local mechanic clean all of them?
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Can't hurt.

Lean aggressively when on the ground.

Aggressively means its about to die at idle and if you advance the throttle without giving it more mixture, it will die.

Ask the mechanic if the engine has a history of this. If it does, there's another problem sometimes.

If not and no other problems exist, he may recommend different plug styles.

Learn where your engine likes to run at idle, mixture wise, and start it slightly rich of there. If it'll run with the mixture pulled out 2", start it with the mixture already out an inch. No point at all, starting it full rich if it'll start leaner.

(Common up here at altitude. Was the coolest "trick" I ever learned watching my mechanic. No prime, he pulled the mixture out an inch and a half and our engine turned over in one blade. I now always start it there. Why have the starter wear out trying to start a full rich mixture?)

Depending on the engine/carb, your idle mixture may also be off.
 
dweyant said:
Just got a call back from the mechanic.

The plug was badly fouled. He cleaned it up and it is running fine, so that is good news.

Now my question is, how can I minimize/prevent this from happening in the future?

He also said the idle sounds just slightly off. Like some of the other plugs might have some fouling. Should I have my local mechanic clean all of them?

Thanks,

-Dan
Click to expand...

Unless you need full power, always run the engine leaned to the point it just barely runs smooth.

Get some wrenches and a gapping tool and service your own plugs.
 
Tom-D said:
carry a plug wrench and clean it your self.

that is owner/operator maintenance (preventive maintenance)
Click to expand...

Agreed, I'm sure the mechanic will show you how to do this if you don't know already.
 
Henning said:
Get some wrenches and a gapping tool and service your own plugs.
Click to expand...

Not a bad idea either. Have the mechanic show you first what to look for, how to clean them, and how to organize them so they go back where you want them, and never drop them and put them back in. ;)

Realistically though, if you're having to pull them all the time to clean them, something else is wrong. Shouldn't have to mess with them.

Speaking of plugs, I went to change the plugs on the Yukon over the weekend and holy crap, the boots are stuck.

I decided I'll let some 20-something get his knuckles all scraped up changing the plugs and wires. I couldn't even get the damn things off with channel locks. And GMC with their stupid heat shields over them... metal rings over the boots. What a pain.

Truck has 108,000 miles. I'm betting no one has ever touched them. Grrrr.

Nice that the Iridiums are pre-gapped these days, though. Kinda cool hiw theyre built too. Tiny little sharp point. Since the Jeep had normal plugs, and Karen's diesel only has glow plugs, I hadnt looked at anything but an airplane plug in years.

Saves a few minutes over the ancient tech in the airplanes. :)
 
denverpilot said:
Not a bad idea either. Have the mechanic show you first what to look for, how to clean them, and how to organize them so they go back where you want them, and never drop them and put them back in. ;)

Realistically though, if you're having to pull them all the time to clean them, something else is wrong. Shouldn't have to mess with them.

Speaking of plugs, I went to change the plugs on the Yukon over the weekend and holy crap, the boots are stuck.

I decided I'll let some 20-something get his knuckles all scraped up changing the plugs and wires. I couldn't even get the damn things off with channel locks. And GMC with their stupid heat shields over them... metal rings over the boots. What a pain.

Truck has 108,000 miles. I'm betting no one has ever touched them. Grrrr.

Nice that the Iridiums are pre-gapped these days, though. Kinda cool hiw theyre built too. Tiny little sharp point. Since the Jeep had normal plugs, and Karen's diesel only has glow plugs, I hadnt looked at anything but an airplane plug in years.

Saves a few minutes over the ancient tech in the airplanes. :)
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I had a pair of boot pulling pliers, they were basically two 'u' shaped blades on a reverse pivot that looked like channel locks that expanded when you squeezed. The ones that always caused me grief were the ones in the little Toyota hemi, the 20R IIRC, that would leave the insert on the plug when you pulled the wire and you had to dig down in the hole to get it out so you could get on the plug. I think I destroyed as many as I saved.:nonod:
 
dweyant said:
The plug was badly fouled. He cleaned it up and it is running fine, so that is good news.

Now my question is, how can I minimize/prevent this from happening in the future?
Click to expand...
Follow the recommendations in Lycoming SL185B.

He also said the idle sounds just slightly off. Like some of the other plugs might have some fouling. Should I have my local mechanic clean all of them?
Click to expand...
Absolutely, especially the bottom plugs (usually they foul the most). And while you're at it, go buy a steel dental pick and a torque wrench and have your mechanic show you how to do it yourself. However, idle being off could also be a carb adjustment problem, so give it a good test run after the plugs are cleaned to see if it's idling properly again.

Ron
 
Geico266 said:
Run cas gas.
Click to expand...

dweyant said:
??

-Dan
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Cas, Car, Potato, Potatoe - what's the difference...

Auto gas will solve the lead fouling issue.

Leaning will help with the lead and eliminate the carbon fouling issue.

Do both and your plugs will look like they came out of a car.

Unless you are burning a ton of oil.
 
Once the plug is lead fouled, there's no amount of "burning off" that's going to solve it. The trick is to know which one is fouled. If you have a engine analyzer, it will tell you which cylinder which greatly speeds up the resolution.
 
flyingron said:
Once the plug is lead fouled, there's no amount of "burning off" that's going to solve it.
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Someone, I'm sure, will be quick to point that you are wrong, because they've done it - but the key part of this statement is "lead fouled". It's quite possible to clean a carbon-fouled (dirty) plug with high power lean operation for a few seconds, but you're not going to get the lead off a lead-fouled plug without pulling the plug.
 
Yep, if it's bridged you are hosed, however most of the time that isn't the case and it can be burned off.
 
flyingron said:
Once the plug is lead fouled, there's no amount of "burning off" that's going to solve it. The trick is to know which one is fouled. If you have a engine analyzer, it will tell you which cylinder which greatly speeds up the resolution.
Click to expand...

Yep, those vibrator tools you stick down to knock it out work pretty good. Two things a pilot-owner is foolish to fly without is an engine analyzer and fuel flow, often combined. They can save you a fortune if you learn to use them because the give early indicators of expensive failures while and where they are relatively cheap to fix. The give a great diagnostic ability of plug strength in operations as you point out as well as nozzle function before you melt a piston.

Fuel flow in over 2500hrs across 4 different planes and 6 engines ha always been within a gallon on fill. How much fuel you have exactly is a really vital piece of intel and gas gauges with modern exceptions suck.
 
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Henning said:
Yep, those vibrator tools you stick down to knock it out work pretty good. Two things a pilot-owner is foolish to fly without is an engine analyzer and fuel flow, often combined. They can save you a fortune if you learn to use them because the give early indicators of expensive failures while and where they are relatively cheap to fix. The give a great diagnostic ability of plug strength in operations as you point out as well as nozzle function before you melt a piston.

Fuel flow in over 2500hrs across 4 different planes and 6 engines ha always been within a gallon on fill. How much fuel you have exactly is a really vital piece of intel and gas gauges with modern exceptions suck.
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Good point. I would have noticed the RPM drop without the JPI, but it made it very easy to tell what and where the problem was.

-Dan
 
Got the plane flown home last night. The engine sounds much better when all the cylinders are firing properly :).

I'm thinking I'd like to go ahead and pull all of the plugs and clean them this weekend, and I have a few questions.

1) Is this a good idea?
2) How do I clean them, just like a car with a wire brush, or is there an approved airplane safe way to do this?
3) Should I make sure they go back in the same spot, or is there some advantage to rotating them. I.e. top to bottom, another cylinder, etc.?
4) Anything else I should think about/know before I attempt this?

Thanks,

-Dan
 
Cleaning them would be recommended, and as you have not done the task yourself on a plane you need to be shown how to do it by an experienced person. (Watch one, Do one, Teach one applies here)
 
dweyant said:
Good point. I would have noticed the RPM drop without the JPI, but it made it very easy to tell what and where the problem was.

-Dan
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You pull in to the mechanics shop and say, "I've fouled the bottom plug on three" and he is not busy good chance you are outa there <$20, if he is busy you can ask to rent some tools for a couple of minutes and clean it. There is always the possibility though that they want $120 minimum or somehow othe ransom you. This is why it's good to carry some tools. Make sure you have the small wrench to hold the wire when you crack off and snug the cap.
 
denverpilot said:
Yup. I lean aggressively on the ground after flying a rental 172RG that fouled plugs all the time many years ago.

When the same happened to me a couple years ago, I knew it wasn't a fouled plug.

The plug wire had broken at the plug connection and had quite literally, fallen off.

New plug wire, it was back to normal.

And now you know why we do mag checks. Amongst other reasons. ;)
Click to expand...

I was never taught to lean on the ground? At what point would one do this? Immediately after start? During runnup? Is it mentioned anyware in the POH?
 
Lean it as much as you can on the ground. Not necessarily immediately after start, but soon after you begin taxi. Lean it so much that it runs rough / cuts out when you goose it.

Go back to POH recommended mixture for runup - takeoff - climb whatever.

Running full rich at low power settings (taxi) really fouls up the plugs.
 
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mirage00 said:
I was never taught to lean on the ground? At what point would one do this? Immediately after start? During runnup? Is it mentioned anyware in the POH?
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Right after its running smooth and you drop the rpm down to minimal, go ahead and pull it back till it stumbles and the give it back 1/4 inch. When the CHTs come online over 110* degrees you can go ahead and trim it back to the point where it hesitates when you hit the throttle, then in slight increments tune that to the point where you can advance the throttle to an immediate 2000 rpm setting without it stumbling. Now take an awl or a sharp knife blade and scribe a reference line somewhere easily seen and set to. This should always provide you with a good setting within an altitude range. If it doesn't, something is different and you should figure out what it is.
 
Henning's procedure is as good as any, if not a tad complex to follow at first. For most airports with long taxi times and long times students/slow pilots (sometimes like me) take to get things set up after engine start and rolling, the steps to wait for higher temps will have taken care of themselves by the time you roll sometimes, even at aggressive lean.

Henning's step-up procedure is to make sure you're not running SO lean that a cylinder isn't really firing well and not warming evenly, and most folks chicken out and richen a bit when it's stumbling that much anyway. ;)

Folks at lower elevations aren't taught to lean on the ground as part of normal ops, more than up here, I've noticed. Starting and taxiing full rich at my 5885' home base will foul a plug in a heartbeat.

We're fiddling with leaning from day one, since we don't take off full-rich either...
 
I was told by my initial instructor "No need to lean below 3000'" oh we'll, I thought, not my fuel and maintenance....
 
There's a good video and set of articles from Mike Busch and some great articles by Deakin the Pelican on leaning. But the general idea is yeah lean a lot while you're on the ground, as much as you pretty much can without the engine shaking or shutting off.
 
denverpilot said:
We're fiddling with leaning from day one, since we don't take off full-rich either...
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Speak for yourself oh normally aspirated one!

Boosted and normalized engines get full rich with full power. Otherwise bad things (detonation) become much more likely to happen. Take-off power? blue and red knobs forward, black one not so much (unless you want to smell hot air as the pop-off lifts). People with fancy automatic wastegates don't have to worry so much 'bout the black knob.
 
Clark1961 said:
Speak for yourself oh normally aspirated one!

Boosted and normalized engines get full rich with full power. Otherwise bad things (detonation) become much more likely to happen. Take-off power? blue and red knobs forward, black one not so much (unless you want to smell hot air as the pop-off lifts). People with fancy automatic wastegates don't have to worry so much 'bout the black knob.
Click to expand...

LOL. True. True.
 
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