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What causes this????

Brantel

Brantel

Well Known Member
I think I found another symptom to why I had a vibration or roughness on my second flight...maybe the first as well but I did not notice it then.

I downloaded my data from the D120 and trended my cht and egt values. All seem to track well with each other until full power for takeoff is applied. Then the #2 egt drops down fast to over 200* less than the others. When reducing power to land, it comes back in line with the rest.

I will post some graphs as soon as I can.

The engine is a carbed O-360 with two slick mags. The mags were uses and the engine is a fresh rebuild with chrome cylinders. FP prop.

I did take the mags apart and the brush is good, the cam ok, the distributor and rotor are well used. The points have some small buggers on them.
The caps test fine.

The plugs looked good on all but #1 the bottom was a little wet.
 
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Miss-Fire

When you pulled the plugs ex. #1. did you look in the upper bore of the plug where the harrness attaches? Was it wet/fuel in there? Rotate the plugs to different cylinders and make note and see if your EGT temps change to that cylinder. I have seen bad and/or cracked insulators in the plug that act up only under higher power settings.

Thomas S.
www.g3ignition.com
 
bad plug...

sounds like it might be a bad plug in that cylinder? fires good under low pressure / power but not under high so the egt goes way down. did you check the plugs in a tester?
 
This is common when a bad plug has a crack

I agree with Stephen. The first thing to check is the plug.

1. Replace both plugs in #2 (don't waste time moving plugs around)

2. If the problem persists then borrow an ignition harness tester and check for a short in the plug wires. This is a portable box that shoves 100,000 volts into the unhooked plug wire and if you have a breakdown in the insulation the spark will jump thru that weak spot. It will also jump the gap if you have a hairline crack in the plastic rotor cap. You can hear it crackle.

3. Chrome cylinders have problems (cast iron rings) breaking in sometimes and you might check the cylinder walls in #2 to see if you have any scratches (broken ring?) that are fouling the plug with oil and preventing ignition. (this is a long shot however)


4. A real long shot would be a valve that 'sticks' and lags preventing full compression in that cylinder. Or it sticks because you have a broken valve spring which allows the engine to run at low rpm but simply can't dance fast enough at higher power. It's hard to see this problem but if you run out of options above you will have to remove the rocker cover, both plugs, move the cylinder to bottom dead center, shove a nylon rope into the cylinder, slowly bring the cylinder up until the rope is crushed against the valves; using a lycoming valve spring depressor compress the cap around the valve, remove the keeper keys and lift off the spring assembly to check for a broken spring (or weak spring). *as a side bar, in the old days if we had a valve that leaked air during a compression check on a lower time engine, we would chuck the loose valve up in a drill motor, lift it off the seat, spin it up and pull it back to clean the garbage off the valve and seat....usually this worked..hahaha....Political correctness prevents me from naming this sort of Valve Job. :)

Good luck..! Let us know what you find.

Bob
 
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One more long shot

Lower temps happen for three reasons. A plug that doesn't fire a cylinder that has low compression and a rich mixture. I've had a PRIMER leak that sucked extra fuel into the manifold causing a rich mixture on one cylinder. like I said LONG SHOT. It was a bad O ring on the primer plunger. Just tossing ideas around.

Bob
 
I should also mention that the CHT appears normal on #2. I will post trend charts in a few...

Brand new harnesses but the plugs came with the engine.
 
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Here are the trends

Here are the trends for the 1st flight and a shorter 2nd flight.

Notice how everything tracks together untill high power is applied. Then the #2 EGT drops off sharp.

1st flight:
6em3yb.jpg

50pnvc.jpg


2nd flight:
if6dt5.jpg

125lzkw.jpg
 
I would think a misfiring/nonfiring plug would cause EGT values to climb rather than fall.
If I turn off one ignition during cruise on my -7A I see the EGTs climb at lease couple of hundred degrees; I have been told that this is because the fuel is still burning during the exhaust cycle.

Mark Olson N407V RV-7A ~550 hours
 
I wouldn't expect EGTs in the 1400s at full rich... 1200s would be numbers I'd expect to see.. (maybe even high 1100s, depending on probe location etc).. All this is just a general thought.... you could nit-pick a bit.. so at best this is just a guideline..
 
The documents and papers I have read have stated that if you turn off a mag, you should see the EGT values climb but if you only see the EGT drop on one cylinder with both mags on, that it indicates a fouled plug, mag or harness issue....

That seems to be constant across all the info sources.

Thanks!!!

molson309 said:
I would think a misfiring/nonfiring plug would cause EGT values to climb rather than fall.
If I turn off one ignition during cruise on my -7A I see the EGTs climb at lease couple of hundred degrees; I have been told that this is because the fuel is still burning during the exhaust cycle.

Mark Olson N407V RV-7A ~550 hours
Click to expand...
 
I have learned one thing....EGT temps are highly subjective with tons of variables!!!

Seems every source I look at for written documentation have different ideas on what normal is for EGT's. They are more consistent on the fact that the important thing is the spread between them and the amount of change that you get from full rich to all the methods of leaning etc.

Thanks!!!

Radomir said:
I wouldn't expect EGTs in the 1400s at full rich... 1200s would be numbers I'd expect to see.. (maybe even high 1100s, depending on probe location etc).. All this is just a general thought.... you could nit-pick a bit.. so at best this is just a guideline..
Click to expand...
 
I have ordered new plugs and new distributor block, distributor gear, rotor gear and points for the mags. Capacitors check good. The harnesses are brand new.

Will install the new plugs, change the parts in the mags and retime them to the engine and try this again...

Thanks!

[email protected] said:
sounds like it might be a bad plug in that cylinder? fires good under low pressure / power but not under high so the egt goes way down. did you check the plugs in a tester?
Click to expand...

OceanBob said:
Lower temps happen for three reasons. A plug that doesn't fire a cylinder that has low compression and a rich mixture. I've had a PRIMER leak that sucked extra fuel into the manifold causing a rich mixture on one cylinder. like I said LONG SHOT. It was a bad O ring on the primer plunger. Just tossing ideas around.



Bob
Click to expand...



OceanBob said:
I agree with Stephen. The first thing to check is the plug.



1. Replace both plugs in #2 (don't waste time moving plugs around)



2. If the problem persists then borrow an ignition harness tester and check for a short in the plug wires. This is a portable box that shoves 100,000 volts into the unhooked plug wire and if you have a breakdown in the insulation the spark will jump thru that weak spot. It will also jump the gap if you have a hairline crack in the plastic rotor cap. You can hear it crackle.



3. Chrome cylinders have problems (cast iron rings) breaking in sometimes and you might check the cylinder walls in #2 to see if you have any scratches (broken ring?) that are fouling the plug with oil and preventing ignition. (this is a long shot however)





4. A real long shot would be a valve that 'sticks' and lags preventing full compression in that cylinder. Or it sticks because you have a broken valve spring which allows the engine to run at low rpm but simply can't dance fast enough at higher power. It's hard to see this problem but if you run out of options above you will have to remove the rocker cover, both plugs, move the cylinder to bottom dead center, shove a nylon rope into the cylinder, slowly bring the cylinder up until the rope is crushed against the valves; using a lycoming valve spring depressor compress the cap around the valve, remove the keeper keys and lift off the spring assembly to check for a broken spring (or weak spring). *as a side bar, in the old days if we had a valve that leaked air during a compression check on a lower time engine, we would chuck the loose valve up in a drill motor, lift it off the seat, spin it up and pull it back to clean the garbage off the valve and seat....usually this worked..hahaha....Political correctness prevents me from naming this sort of Valve Job. :)



Good luck..! Let us know what you find.



Bob
Click to expand...
 
What model carb do you have?? I agree with Radomir that your EGTs seem a bit high ( I know the numbers are a bit subjective, but I would be concerned with numbers that high)--A test would be to lean to peak and see how much rise you obtain. I would like to see a good 150 degrees rich of peak when running full rich. I think Don at Airflow says more like 175-225 degrees.
see this for a little more info-- http://www.vansairforce.com/community/showthread.php?t=30115&highlight=4164+carb
 
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It is a 10-3878 that was modified by Bart at Aerosport to be richer for use on an RV.

jabarr said:
What model carb do you have?? I agree with Radomir that your EGTs seem a bit high ( I know the numbers are a bit subjective, but I would be concerned with numbers that high)--A test would be to lean to peak and see how much rise you obtain. I would like to see a good 150 degrees rich of peak when running full rich. I think Don at Airflow says more like 175-225 degrees.
see this for a little more info-- http://www.vansairforce.com/community/showthread.php?t=30115&highlight=4164+carb
Click to expand...
 
I recently had this problem on another type of plane,,,changed the harness and had the mags overhauled,,still no good,,,tested the brand new unison spark plugs in a bomb tester and 2 were not firing under pressure, the plugs had less than 5 hours on them. I tested some other brand new. never run unison plugs I had and 1 of those was also bad. I switched all to champion and the problem is fixed. If you have unison plugs, I'd consider switching them.
 
I had a similiar viberation on an earlier plane I built I

first noticed after takeoff and during climb out. Scared me for a couple flights until I mentioned it to a Bud who advised me to tap the brakes after take off as the wheels were still spining. Sure enough that was the fix. You might try that before taking your plane apart. Best of luck, Bill RV-8a wiring
 
Bill Phillips said:
first noticed after takeoff and during climb out. Scared me for a couple flights until I mentioned it to a Bud who advised me to tap the brakes after take off as the wheels were still spining. Sure enough that was the fix. You might try that before taking your plane apart. Best of luck, Bill RV-8a wiring
Click to expand...

Vibration, sure - but I don't think that would cause an EGT drop! :D
 
could be just the way it is?

I get both a vibration and EGT drop at full power too.

So I added an engine monitor to my tired old O-235. At cruise or low power, I get EGT spreads in the 40-60 degree range.... but at full throttle my back two cylinders (3 & 4) run about 200 degrees cooler EGT. There is a noticable roughness also. I've been told this is just a byproduct of poor fuel/air distribution inherent to the carb installation. The engine seems to be making rated power (RPM) and more or less "performs" as expected for a high time little engine. I have recently rebuilt mags, replaced plugs & wires, and set valve tappet clearance. All with no real change.
 
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engine problem

Check your air induction tube for that cylinder. Make sure it is not leaking. It could be going well lean of peak which could lower the temp drastically. We had a similar problem on a C182. After a mountain of money, tightening a hose clamp fixed the problem. Won't cost you anything to try it.

Dave Nellis
 
truflite said:
Check your air induction tube for that cylinder. Make sure it is not leaking. It could be going well lean of peak which could lower the temp drastically. We had a similar problem on a C182. After a mountain of money, tightening a hose clamp fixed the problem. Won't cost you anything to try it.

Dave Nellis
Click to expand...

I disagree - the problem manifests itself at high power, which is high manifold pressure. A leaking induction tube is a possibility, but it would result in a rich-of-peak scenario at high power, not lean. At low power settings it would leak more air into the induction, requiring an abnormally rich mixture to produce smooth running. At high power setting the pressure differential across the leak drops to nil and no additional air comes through, but the mixture is still adjusted on the rich side, producing a mixture rich enough to depress the EGT.

I would suggest leaning the mixture at full power slowly in flight until nearly lean cut-off, and monitoring that EGT/CHT - that may tell you a story.
 
Induction tubes are always a good source of rough...

truflite said:
Check your air induction tube for that cylinder. Make sure it is not leaking.
Click to expand...
I disagree with Airguy- Always check the induction tubes anyway-
They will be sucking excess air- not fuel (lean of peak condition and rough running that will lesson on power reduction) Been there done that-

I also see this minor rough running in a full power takeoff on our 6A- Also have a carb with dual mags on a CS speed 0360- I also attribute this to the excess and unequal fuel distribution with a full power to one or two of the cylinders. The experiment was to pull a little power after initial climb and it smooth’s out to a happy power setting- Also adjust mixture early in the climb at around 3,500 or lower for my engine/carb combo- doesn't take much leaning to smooth this out- So I think your EGT drop is excess fuel in that #2 Cyl. One of the the plug conditions at high pressure may also be it.
my .02$. Let us know what you find!
 
AZtailwind said:
I disagree with Airguy- Always check the induction tubes anyway-
They will be sucking excess air- not fuel (lean of peak condition and rough running that will lesson on power reduction) Been there done that-

I also see this minor rough running in a full power takeoff on our 6A- Also have a carb with dual mags on a CS speed 0360- I also attribute this to the excess and unequal fuel distribution with a full power to one or two of the cylinders. The experiment was to pull a little power after initial climb and it smooth’s out to a happy power setting- Also adjust mixture early in the climb at around 3,500 or lower for my engine/carb combo- doesn't take much leaning to smooth this out- So I think your EGT drop is excess fuel in that #2 Cyl. One of the the plug conditions at high pressure may also be it.
my .02$. Let us know what you find!
Click to expand...

Ok, now I'm confused - you say you disagree with my logic (lean vs rich on #2) but yet you come to the same conclusion I did for the same scenario (rich on #2)? If the induction tube is leaking, it's going to leak MORE at low power (low manifold pressure, more air being sucked in) and create a lean condition. If the carb is initially set up to produce smooth operation at this point (which it obviously would be on a new install), then you would not necessarily realize you had an induction leak. At high power (high manifold pressure) there is no pressure differential to drive that additional air through the leak, and the mixture is now excessively rich. This is not a condition that would be easily recognized on the ground, but would manifest itself at full power in the air.

I was not disagreeing about the induction tube being a possible problem point - but rather the result of that leak being a rich condition rather than a lean one (at WOT).
 
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How would the enrichment valve system play into this situation???

My carb was purchased from a man who bought it several years ago new with an engine that he bought from Aerosport. He stated that he pulled it off the engine and installed FI before ever running the engine and the carb sat on the shelf for several years. He also stated and it was confirmed by Bart at Aerosport that the carb was modified to richen it up for better use on an RV.

When I got the carb, I opened it up and cleaned it and changed the float and also checked that the main jet was truly larger than a stock 10-3878 and it was.

I cleaned everything very well and put it all back together.

I did not tear into the enrichment valve area since it had a lead seal on it.

Could the enrichement valve be plugged or blocked open?

I am not going to get too worried at this point since the engine is a new rebuild with about 30 minutes of flying time on it. It is running mineral oil at this time and I doubt it is even close to broke in yet.

The fuel flows are about what I would expect for a FP 180hp engine on that day and pressure altitude so I do not think it is running too lean. I have no idea if the fuel flow sensor is accurate yet as it only has the Dynon default K-factor in the EMS at this time. After I get some fuel burned, I can check to see how close it is to actual.

Thanks for all the help.. I am stuck up here in Augusta WI for this week and all I have to do is think about flying my new airplane!!!!
 
I agree to dissagree

airguy said:
Ok, now I'm confused - you say you disagree with my logic (lean vs rich on #2) but yet you come to the same conclusion
Click to expand...

Hay Greg, I agree with your conclusion :p
it is probably not a leaking induction tube-
It may be a rich unbalanced nature of #2 Cyl getting a little too much fuel. My 6 does the same thing though I have not investigated it with an EM.

I disagree that induction problems cause a fuel rich of peak issue: your first post stated induction leakage is ?a rich of peak issue? you probably meant lean of peak?
This is from experience: An induction leak will make the roughness across the whole power band with a lower power setting being the smoothest. Almost as bad as if you lost a cylinder. The lean cylinder or cylinders will be lean of peak and running hot. It can be an expen$ive leak!I was just saying this was something to allways check but probably not the issue.

Also for Brantel- RV?s do get a little more MP/Power due to the ram air effect of the racing style air intake. Though I?m not sure is it deserves a larger main jet to ballance and increase of +2 MP at high cruse(??). You are getting into the art/science of carburetors here- maybe a call to Malon is in order. Or maybe it is a spark plug?
 
low egt

Have you looked at something as simple as a bad connection, bad crimp in an egt wire?

It might have reasonable connection until the vibration at max power comes in and then the system is averaging the noisy data.
 
Swap....

NDrv8r said:
Have you looked at something as simple as a bad connection, bad crimp in an egt wire?

It might have reasonable connection until the vibration at max power comes in and then the system is averaging the noisy data.
Click to expand...

...EGT probes and see if the problem moves with the probe.
 
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AZtailwind said:
I disagree that induction problems cause a fuel rich of peak issue: your first post stated induction leakage is “a rich of peak issue” you probably meant lean of peak?
This is from experience: An induction leak will make the roughness across the whole power band with a lower power setting being the smoothest. Almost as bad as if you lost a cylinder. The lean cylinder or cylinders will be lean of peak and running hot. It can be an expen$ive leak!I was just saying this was something to allways check but probably not the issue.
Click to expand...

On an airplane with a properly adjusted carb (or injector) such that the mixture is correct, and THEN an induction leak occurs, yes I would agree with your statement.

In this case however, my premise was that the induction leak could be present from the first start and was not recognized. The carb was set up to result in smooth running at ground-power levels (where additional air is being drawn into the tube post-carb), which would result in a slightly over-rich mixture if the induction leak was not present. At full power the manifold pressure is essentially the same as atmospheric and the leak is essentially zero, which would result in a richer mixture than desired. If you are already running a full or nearly-full rich mixture (as you certainly would on engine break-in during Phase I) then this could very well be rich enough on one cylinder to drop the EGT.

I would also think however, that for my scenario to be true, the leak would need to be at the throttle body and not one individual cylinder, in order to get the engine to idle smoothly with the leak present.
 
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