Black exhaust soot??

Discussion in 'Maintenance Bay' started by jmarine225, Nov 8, 2020.

  1. jmarine225

    jmarine225 Pre-takeoff checklist

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    So I recently had a magneto overhauled and replaced along with the 4 plugs to this magneto. The aircraft is a Piper Cherokee. I’ve noticed since having this replaced some black exhaust can be seen on the nose wheel, especially if the plane is leaned out during flight. The EGT is running at 200 degrees or so while in cruise and not leaned out. It seems the more it’s leaned out the more black soot and higher egt now. Not sure of this new magneto is the cause or if it’s something else, again.
     
  2. Tantalum

    Tantalum Final Approach

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    I always was told black soot meant it was too rich

    however.. the above seems at odds with "It seems the more it’s leaned out the more black soot"
     
  3. GRG55

    GRG55 Final Approach

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    Black soot in the exhaust means its running too rich. I'm presuming the overhauled magneto checks out okay on the runups.

    A few things to check:
    - Air filter and air intake system, to make sure it's not clogged
    - Make sure your new spark plugs are the correct heat range for the model of Lycoming engine you have
    - Are you getting oil past the rings in any of the cylinders? - your plugs, especially the lower ones, will usually show if that is happening.
     
  4. jmarine225

    jmarine225 Pre-takeoff checklist

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    In regards to this, the mechanic replaced all 4 bottom plugs as he said they were out of spec. There wasn’t any problem before these were replaced.
     
  5. GRG55

    GRG55 Final Approach

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    One of the two bolded statements above may be incorrect. Normally (on the 4-cyl Lycomings I am familiar with) each magneto fires 2 top plugs on one side of the engine and 2 bottom plugs on the opposite side. You can check that easily by tracing the ignition wires from each magneto to the spark plugs it fires.

    The bottom plugs take a bit of a beating, so not unusual to change them. However, the plugs should be rotated when they are serviced so the full set in the engine wears fairly evenly. If that was done through the life of your plugs then the top plugs should not be too far behind in terms of needing to be replaced also.

    You say there was no problem before the magneto was overhauled and the plugs were replaced. Normally the first thing(s) to check is whatever was last changed.

    In addition to what I listed earlier, you might also want to double check the timing on the overhauled magneto. If it is mis-timed (e.g. timed to fire too late) you may not be getting complete combustion of the fuel/air mix.

    If it is black soot you are getting I would say three of your most likely causes are:
    1. Mixture too rich (air filter plugged, mixture control not working properly, carb heat control not closing, etc);
    2. Incomplete combustion (ignition or timing issue);
    3. Excessive oil entering at least one cylinder (rings or valve guides - when was your last compression test and what did it indicate?).
    Paging @Dan Thomas
     
    Last edited: Nov 8, 2020
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  6. Stewartb

    Stewartb Final Approach

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    EGT is 200*??? In leaned cruise it should be around 1400*.
     
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  7. jmarine225

    jmarine225 Pre-takeoff checklist

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    Curious on this now. If it helps it’s a simple EGT gauge. Full rich it’s been running at the second large indicator line. Gauge says 25 degrees so I was going off that. It wasn’t running that hot before these replacements. If I lean at cruise that gauge goes up even higher.
     
  8. Salty

    Salty Final Approach

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    The actual EGT isn’t relevant, it’s the delta from the peak that matters, but yeah, > 1000 degrees is a more sane value than 200. Many old gauges don’t even have numbers.
     
  9. Hang 4

    Hang 4 Cleared for Takeoff

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    Was the oil changed when the other work was done? If it was overfilled (which is filled to 8 quarts on the dipstick, Lycoming 360's like to be under 7) it could deposit stuff on the front wheel pant.
     
  10. Tom-D

    Tom-D Taxi to Parking

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    How is the black stuff getting from the engine to the nose wheel? (flying) Wouldn't it be over the belly too?
     
  11. Jumpmaster

    Jumpmaster Pre-takeoff checklist

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    I run myTiger between 1400 -1450F on the EGT in cruise which is about 9.7 gph on a Lycoming 0-360 at 2600 RPM. Your EGT gauge must be way off or the marks represent greater values than what you might think. I would suggest you lean the engine the way you should have been taught - lean to engine roughness and then enriched slightly and see what happens. The engine will let you know if it’s happy or not.
     
  12. jmarine225

    jmarine225 Pre-takeoff checklist

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    It’s an o-320 engine. It’s definitely exhaust on the wheel pant. I’ve wiped it off and checked it. Also the oil is around 6 where it seems happy.
     
  13. jmarine225

    jmarine225 Pre-takeoff checklist

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    Actually didn’t check the belly but he wheel pant is white so it’s obvious.
     
  14. jmarine225

    jmarine225 Pre-takeoff checklist

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    I normally would do this but that egt gauge was rising continuously which it’s never done. The engine seems to be running fine. My concern is a cylinder overheating if the egt is continuing to climb, damaging the engine.
     
  15. GRG55

    GRG55 Final Approach

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    What is on the inside of the exhaust stack itself?
     
  16. jmarine225

    jmarine225 Pre-takeoff checklist

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    I wiped the inside with my finger and it’s black dust in there.
     
  17. Omalley1537

    Omalley1537 Line Up and Wait

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    Two thoughts-

    Your EGT gauge may be for adjusting lean or rich of peak, and the degrees may represent that and not an actual reading.

    Were the replacement plugs Champions? Still a few of the garbage ones sitting on shelves with dust on them.
     
  18. jmarine225

    jmarine225 Pre-takeoff checklist

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    Replaced with tempest plugs. All plugs in the engine are less than 6 months old now.
     
  19. jmarine225

    jmarine225 Pre-takeoff checklist

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    Also a compression check at the last annual indicated all cylinders were mid to high 70’s. Approx 450 hours on the engine smoh
     
  20. smv

    smv Pattern Altitude

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    Are there actual numbers on your EGT or just a bunch of hash marks and a notation that says "25° per divison"? Being familiar with Pipers, my guess is the latter.

    The red needle is designed to be moved to "Peak" temp for those conditions on that day. Leaning is performed (either ROP or LOP) based upon where you place that needle to line up with peak temp counting 25° for each line away from peak.
     
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  21. jmarine225

    jmarine225 Pre-takeoff checklist

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    Yeah that is the gauge. I saw 25 and was t sure what that meant, so thanks for filling me in. So at full rich it is running at the 8th line, 200. It normally is lower than that. I understand the red line, lean, rich aspects but the gauge is now reading higher than before after having this work done. Hope that explains it a bit. Maybe it’s supposed to be higher and with the new plugs and mag that helped it? But then the black exhaust on my wheel pant which never occurred before.
     
  22. Stewartb

    Stewartb Final Approach

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    The simple Alcor gauge doesn't indicate total temperature. The asterisk is there to set a peak EGT value for the primary needle and the secondary needle can be used any way you choose. Here are the instructions for indexing the needle on the asterisk at peak. Some guys lean until there's a stumble, enrich just enough to smooth it out, and call that peak. Set the red needle 100* rich for high power ops max EGT, cruise at peak.

    https://alcorinc.com/PDF/59185.pdf
     
    Last edited: Nov 9, 2020
  23. jmarine225

    jmarine225 Pre-takeoff checklist

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    Thanks. Still doesn’t help explain to me why the gauge is reading higher than it has been and the black exhaust on the wheel pant all of a sudden.
     
  24. Stewartb

    Stewartb Final Approach

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    Find peak and lean properly. You don't need the gauge for that. See if the soot issue resolves itself. If not, take it back to your mechanic.
     
    Last edited: Nov 9, 2020
  25. 455 Bravo Uniform

    455 Bravo Uniform En-Route

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    I’ve seen “black soot” actually from aluminum parts rubbing. Make sure what you’re seeing is from exhaust and not aluminum dust/abrasion (aluminum cowl rubbing against exhaust pipe; loose rivets, aka smoking rivets; etc.)

    If you had spark issues and fixed them, I would expect EGTs to go up. Your gauge is a “relative” gauge, no exact temperature shown. Read your POH or your favorite aviation website on how to lean using this gauge, to eliminate “rich soot” if that’s actually the case.

    And yeah, take it back to your mechanic.
     
  26. jmarine225

    jmarine225 Pre-takeoff checklist

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    So maybe I’m looking at it wrong. All 4 plugs needed to replaced, so now all plugs are less than 6 months old. I’m guessing this would make the engine run hotter and also require more of a mixture lean when could be done.
     
  27. MauleSkinner

    MauleSkinner Final Approach

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    Get some instruction on leaning.
     
  28. flyingbrit

    flyingbrit Pre-takeoff checklist

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    What type of fuel are you using? With 100LL or other leaded fuel I would expect grey deposits from the exhaust. With today's Mogas or other no-lead fuel I would expect black deposits.
     
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  29. Domenick

    Domenick Pre-takeoff checklist

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    How does black soot get 12" or more below the exhaust stack to the wheel pant? During flight there is no way the exhaust gases get that close to the wheel pant. If it did, I'd think the fiberglass would scorch.

    Is it soot or dusty oil? Pull the bottom plugs and check their type and condition.
     
  30. Dan Thomas

    Dan Thomas Final Approach

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    Dry black soot means rich. Greasy black soot means oil. Grey or light brown means nicely leaned. Soot on a wheel pant might be from exhaust water vapor condensation in the muffler immediately after startup on a cool day, and that water will pick up soot from inside and drip it on something like a wheelpant. If the pilot goes full rich on starting descent and keeps it there until he shuts down he could get lots of soot in there ready for the next cold start.

    If the exhaust is to the right of the wheelpant and ahead of it some, the prop's rotation will carry any drips inboard enough to possibly nail that pant.

    EGT gauges don't have a Zero line. They don't even start reading until the exhaust is getting pretty hot.

    [​IMG]
     
  31. jmarine225

    jmarine225 Pre-takeoff checklist

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    All bottom plugs were just replaced with the magneto. This gauge is similar to mine. I had an app look at it and said the engine is running better than ever. On this gauge, Unleaned at cruise, the engine is at 1400. It begins climbing up to the 1500 range upon leaning it out, rich of prime. If those numbers seem okay, then I’ll let it be. The soot is like a dusty soot which can easily be wiped off with a paper towel.
     
  32. Tom-D

    Tom-D Taxi to Parking

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    But how did it get on the wheel pant??
     
  33. jmarine225

    jmarine225 Pre-takeoff checklist

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    I’m guessing during startup and run up. Only two options.
     
  34. Tom-D

    Tom-D Taxi to Parking

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    Wash the aircraft, pay more attention, watch when it happens
     
  35. Dan Thomas

    Dan Thomas Final Approach

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    I said this in my post:
    "If the exhaust is to the right of the wheelpant and ahead of it some, the prop's rotation will carry any drips inboard enough to possibly nail that pant."
     
  36. Tom-D

    Tom-D Taxi to Parking

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    How many times does this happen?
     
  37. Stewartb

    Stewartb Final Approach

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    You guys need to get over yourselves. The OP apparently didn't understand leaning or his EGT gauge. You have the opportunity to teach. Teach.
     
  38. jmarine225

    jmarine225 Pre-takeoff checklist

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    Well this quote is incorrect. I understand leaning, how to lean, when to lean etc. I dont understand the sudden high temps on the gauge and the black exhaust which is all of a sudden after a magneto and plugs replacement.
     
  39. Tom-D

    Tom-D Taxi to Parking

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    How do you know it needs leaning? Have you had hands on it?
    Has anyone had hands on it?
    or are we guessing again?
     
  40. Tom-D

    Tom-D Taxi to Parking

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    My suggestion is, ask your A&P for help.