EGT increase

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Magisterol

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Hello Guys. A question that arises from my last flight. I have an O-320 in front of a Mustang II and in cruise, I do mag check every 1/2 hr or so and before I start down. I realized that my EGT goes up 50deg F, along with the normal rpm drop, while on single mag. Is it normal? I only have EGT and CHT probes on 1 cylinder : #3 and #4 respectively. It almost looks like the mixture is getting leaner....
 

TFF

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It is normal and is a good way to know you have a bad mag.

Flying piston helicopters, you don’t do mag checks in the air because the engine will stop cold Nothing windmilling, you are doing an autorotation. Unless you have a un-helicopter like altitude, flying high, you don’t have time for a restart.

The EGT rise is a good way to know that where you are stopping, you will be calling someone with tools.

Two stories. I know someone who destroyed a Cirrus engine once he detected the bad mag. They did not switch off the bad one but went full throttle to get home quicker. Totally toasted the engine when occasionally the bad mag would fire randomly when the teeth would catch. That instance finding the bad mag and switching off was the right thing. The other is helicopter. The person who taught my helicopter CFI to fly helicopters tested his mag at low altitude. Killed him when he did not have time to do a proper auto because his hand was on the key instead of control just long enough. A good engine monitor is real handy so you don’t need to test in the air unless you really suspect a bad mag.
 

Magisterol

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It is normal and is a good way to know you have a bad mag.

Flying piston helicopters, you don’t do mag checks in the air because the engine will stop cold Nothing windmilling, you are doing an autorotation. Unless you have a un-helicopter like altitude, flying high, you don’t have time for a restart.

The EGT rise is a good way to know that where you are stopping, you will be calling someone with tools.

Two stories. I know someone who destroyed a Cirrus engine once he detected the bad mag. They did not switch off the bad one but went full throttle to get home quicker. Totally toasted the engine when occasionally the bad mag would fire randomly when the teeth would catch. That instance finding the bad mag and switching off was the right thing. The other is helicopter. The person who taught my helicopter CFI to fly helicopters tested his mag at low altitude. Killed him when he did not have time to do a proper auto because his hand was on the key instead of control just long enough. A good engine monitor is real handy so you don’t need to test in the air unless you really suspect a bad mag.
Ok. So what you guys are saying is that both my mags are shot? This is not good. I had them tested this year at my annual and the rpm drop is around 100rpm. Well, I should probably look for an AME and do another test before I decide to change them. The mags have about 270hrs since last check. They are Bendix.
 

TFF

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Mags require maintenance. The points need to be set about every 150 hours for peak efficiency. Most mag drops are points wearing which retards timing. Most mechanics just bump the timing over to compensate. That gets the timing correct but the smaller points gap means less electricity to spark the plug. Loss of overall efficiency. The gap needs adjusted which is easy.

Most mechanics are scared to open a mag today. They just want to R&R the thing on your dime. Age can be an issue. 12 year old mags with 200 hours are not equal to 2 year old mags with 200 hours. You have to open them up and take stock of condition.

Bendix are the easiest to work on and are my preference over slick.
 

rv6ejguy

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Ok. So what you guys are saying is that both my mags are shot? This is not good. I had them tested this year at my annual and the rpm drop is around 100rpm. Well, I should probably look for an AME and do another test before I decide to change them. The mags have about 270hrs since last check. They are Bendix.
100 rpm drop is getting up there if you test at 1800 rpm. Maybe time for a peek inside by a good mag shop. Alternately, there are plenty of electronic ignition choices out there which don't require much maintenance.
 

Toobuilder

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Ok. So what you guys are saying is that both my mags are shot? This is not good. I had them tested this year at my annual and the rpm drop is around 100rpm. Well, I should probably look for an AME and do another test before I decide to change them. The mags have about 270hrs since last check. They are Bendix.
An end of the runway mag check does little more than indicate the mags are somewhat functional. The in-flight, LOP mag check tells you a lot more about their health because they are stressed more heavily. And yes, the EGT rise is normal. That said, if you are doing the pre takeoff mag check, ensure you are leaned to highest RPM. Mixture has a big impact on the "mag drop", so leaning to peak RPM removes that variable.
 
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Magisterol

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An end of the runway mag check does little more than indicate the mags are somewhat functional. The in flight, LOP mag chek tells you a lot more about their health because they are stressed more heavily. And yes, the EGT rise is normal. That said, if you are doing the pre takoff mag check, ensure you are leaned to highest RPM. Mixture has a big impact on the "mag drop", so leaning to peak RPM removes that variable.
I think I forgot to say that all this is happening in flight. I run the engine btwn 2400 and 2500 rpm at 5500 to 6500 ft. I talked to an AME from our club and he said too that it is normal, because the flame front moves slower and the flame gets thro the exhaust valve when it opens, because the burning is not done as quick as with 2 sparks. I will have to check the timing and ask the guys to adjust the gap. Mind you exactly what TFF said, most mechanics just bump the timing so they don’t have to open it...Anyway, thanks for the info. The mechanic at our club is very helpful, so I will fly the air there for a better testing.
 

TFF

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The Bendix mags I set up get the points set to .017”. I don’t accept close. That gives the points the longest time before readjustment. If adjusted to something like .015 or .012 just means they need adjustment sooner. New points need readjust in 25 hours as they take a set.
 

Magisterol

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The Bendix mags I set up get the points set to .017”. I don’t accept close. That gives the points the longest time before readjustment. If adjusted to something like .015 or .012 just means they need adjustment sooner. New points need readjust in 25 hours as they take a set.
I will talk to the AME. Thanks.
 

wsimpso1

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Ok. So what you guys are saying is that both my mags are shot? This is not good. I had them tested this year at my annual and the rpm drop is around 100rpm. Well, I should probably look for an AME and do another test before I decide to change them. The mags have about 270hrs since last check. They are Bendix.
I read the whole thread twice, and no one said your magnetos are shot. Please read what was written, and try not to read in things that just were not there...

Getting a modest rise in EGT and a modest drop in rpm while on one mag IS normal. Stay on one magneto and CHT will usually go up a little too, but that takes a couple minutes. EGT's and rpm returning to where they were before the mag check is then expected, and if it does, you are good to go.

The explanation you gave us for why the EGT is higher is approximately correct. Rigorously, you need both plugs to get best efficiency in these big cylinders we have in airplanes. Fire only one plug and the fire in much of the combustion chamber is late. All of the burning is done while the piston is still quite far up in the bore, but being late means we extract less power during the expansion, and more energy is still in the gases when the exhaust valve opens. Higher EGT's and higher CHT's sometimes too. And less power, which you see with the drop in rpm.

If you had a mag go off-line, you would see a similar thing happen. EGT's up a little, rpm down a little, CHT creeping up some. Then you might start the usual checks of switching to one mag at a time, reduce power a little if CHT's are going too high, maybe check that you are leaned properly, etc.

Now please tell us why you are so concerned about your mags that you do multiple mag checks per flight. Most of us do one check before committing to flight. If we are concerned about engine condition and we are fuel injected, we might do a GAMI check once in a while. A GAMI check will show magneto weakness, mixture way off in one or more cylinders, and other things that are not right...

Billski
 

Magisterol

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I read the whole thread twice, and no one said your magnetos are shot. Please read what was written, and try not to read in things that just were not there...

Getting a modest rise in EGT and a modest drop in rpm while on one mag IS normal. Stay on one magneto and CHT will usually go up a little too, but that takes a couple minutes. EGT's and rpm returning to where they were before the mag check is then expected, and if it does, you are good to go.

The explanation you gave us for why the EGT is higher is approximately correct. Rigorously, you need both plugs to get best efficiency in these big cylinders we have in airplanes. Fire only one plug and the fire in much of the combustion chamber is late. All of the burning is done while the piston is still quite far up in the bore, but being late means we extract less power during the expansion, and more energy is still in the gases when the exhaust valve opens. Higher EGT's and higher CHT's sometimes too. And less power, which you see with the drop in rpm.

If you had a mag go off-line, you would see a similar thing happen. EGT's up a little, rpm down a little, CHT creeping up some. Then you might start the usual checks of switching to one mag at a time, reduce power a little if CHT's are going too high, maybe check that you are leaned properly, etc.

Now please tell us why you are so concerned about your mags that you do multiple mag checks per flight. Most of us do one check before committing to flight. If we are concerned about engine condition and we are fuel injected, we might do a GAMI check once in a while. A GAMI check will show magneto weakness, mixture way off in one or more cylinders, and other things that are not right...

Billski
I guess I should have said the mags might be on the way out, not that they are shot. Anyway, the reason I do multiple mag checks is that ever since I bought the airplane, the engine in cruise sounds like is skipping a beat from time to time, so I am trying to find out if it is the mags, carburation or electrical. I had the carb checked out and they did the SB 22. I had the mags checked out and it checked ok. At some point I will have to get to the electrical to change the whole thing, because from time to time the compass is swinging by itself, so I am suspecting a mesh from a wire that was grounding is touching metal part somewhere creating a loop. The other thing that sent me to carburation is that below 2000rpm or so the engine is getting rough. It doesn’t change with mixture setting or carb heat or mag check.
 

TFF

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Just thoughts.
I would check the P leads and the switch. Some switches have ADs against them. Does the engine raise RPM just before cutoff? Other things like carb part number matches the right size engine? A 0-360 carb on a O-320 or vice versa will not be jetted right even if the outside looks the same. What is the age of the mag internals? Does it do the hiccup on either tank setting? It could be a tank vent or pickup problem. Do the bottom plugs lead foul? If it has a fuel boost pump, does it do it with it on or off?
 

Magisterol

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Just thoughts.
I would check the P leads and the switch. Some switches have ADs against them. Does the engine raise RPM just before cutoff? Other things like carb part number matches the right size engine? A 0-360 carb on a O-320 or vice versa will not be jetted right even if the outside looks the same. What is the age of the mag internals? Does it do the hiccup on either tank setting? It could be a tank vent or pickup problem. Do the bottom plugs lead foul? If it has a fuel boost pump, does it do it with it on or off?
I had the switch checked when they did the mags. They took the mags apart and change the condenser on one, and took the ignition switch apart. They tho maybe they are dirty inside on the contact points. It looked like out of the box...
There is no rpm rise on shutdown. The idle mixture is lean. If I enrich it, the engine is getting even rougher. The richer the idle mixture, the rougher the engine below 2000rpm. The AME said it doesn’t make any sense because the idle mixture above 1500rpm or so shouldn’t affect the engine. I don know what to say. I only call it as I see it.
The carb is matched with the engine. They looks at it when they did SB22. They asked me what O-320 I have. I told them it is an O-320 E2A with 8.5:1 compression pistons. They said the carb is ok.
Well, the age of the mags..... The airplane was built in 1999 and since then it has less than 300 hrs. It doesn’t say anywhere that he did a mag overhaul.
It only has one tank and no boost pump.
I am suspecting that all these things are happening because the airplane was hardly flying for the 4-5 years before I bought it...It flew less than 10hrs in that period.
 

rv6ejguy

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Seems to me there was a SB or AD on some Lycoming carbs where a jet comes loose. My friend almost had a forced landing coming back from Osh a couple years ago due to this.

If mixture doesn't change the roughness, maybe not a carb/ mixture problem though, look to the ignition- mags, leads, plugs.

Finally, Lycomings sometimes get stucking valves. Usually begins intermittently and finally progresses to fully stuck and a bent pushrod in some cases. If it's not ignition or fuel, it's something mechanical.
 

Magisterol

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Seems to me there was a SB or AD on some Lycoming carbs where a jet comes loose. My friend almost had a forced landing coming back from Osh a couple years ago due to this.

If mixture doesn't change the roughness, maybe not a carb/ mixture problem though, look to the ignition- mags, leads, plugs.

Finally, Lycomings sometimes get stucking valves. Usually begins intermittently and finally progresses to fully stuck and a bent pushrod in some cases. If it's not ignition or fuel, it's something mechanical.
It is a work in progress. I am still looking for an AME that wants to get in the airplane with me and hear it by himself. So far no luck. The airplane flies ok. The longest flight I did was 2hrs, but I understand most of the AME’s don’t want to get on homebuilds. I am hopping an AME has a better understanding on what is happening by listening to it than I do. Well, until then.... Keep on looking.
 

rv6ejguy

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It is a work in progress. I am still looking for an AME that wants to get in the airplane with me and hear it by himself. So far no luck. The airplane flies ok. The longest flight I did was 2hrs, but I understand most of the AME’s don’t want to get on homebuilds. I am hopping an AME has a better understanding on what is happening by listening to it than I do. Well, until then.... Keep on looking.
Where are you located?
 

Magisterol

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Ok, a bit too far. I have an excellent AME friend with mobile service who covers AB, SK and BC.
Thanks anyway. I a pretty sure I can find someone around here too, but I need time to talk to a lot of AME. But it is expensive. I have 5 mechanics looked at my airplane and nothing is below 150 bucks. That wouldn’t be a problem. The problem is that on the ground nobody can find anything and they don't want to fly....
 
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