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pmccarthy

Clearing a fouled plug

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Today I was stuck in the middle of South Australia with a fouled plug. The right mag had been running rough for months, but the drop was not outside limits. Today it nearly shook the engine off its mounts.

 

i tried running it lean for a few minutes, no go. It’s a Lycoming 0360. I rang a mate who is a LAME and he said do that again, but this time pull in carb heat to shock the plug. I did (a few times) and it worked. Smooth running on either mag. This may be common knowledge but somehow I had missed the briefing, and was looking to spend an unplanned night in a strange town. 

 

I had had a spare plug on board, but no spanner. Found out a plumbing tube spanner will fit, from a hardware store. Fortunately that was plan B and not needed.

 

PAX are happy that the delay was only an hour. So my messages are:

 

know how to clear a fouled plug (I thought I did but didn’t)

if you carry a spare plug, also carry a tube spanner to fit.

 

a few years ago I had a flat tyre and that taught me to carry all the tools needed to change one. A spare anything is no use if you can’t change it.

 

Happy New Year.

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Posted (edited)

One of the things I learnt to carry in a car, is a short bit of pipe to go over and extend the wheel nut spanner.

Easy to loosen the nuts with extention on, but just tighten with spanner only.

 

My aircraft came with a little orange "Rotax" bag. This came with a tube spanner for the plugs. I just added two spare spark plugs.

 

Edited by Downunder

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Well that's interesting. What's the basic science behind it I wonder. Why did it work so well when normal methods didn't?

Doesn't appear to be in the Lycoming operator manual. Please report yourself to nearest CASA office (within 7 days) for prosecution.😀

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1 hour ago, 440032 said:

Well that's interesting. What's the basic science behind it I wonder. Why did it work so well when normal methods didn't?

Doesn't appear to be in the Lycoming operator manual. Please report yourself to nearest CASA office (within 7 days) for prosecution.😀

I suspect it was, in effect,  just leaning it a bit more.

Not sure how it could “shock the plug”. After all nothing really changed except the fuel:air ratio. The temp change from sucking in pre-warmed  air would be minuscule compared to the temp at the plug. 

 

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Posted (edited)

 Its easy to work out which cylinder. Before you get the engine too hot run it  where it's rough and feel the exhaust pipes where they leave the head. Just touch it quickly rather than burning your hand

  The fouling is usually lead deposits and you run the motor lean at about 1800 revs on both mags for a few minutes . with the COWL ON.. it's usually the bottom plugs that  lead foul on a Continental or Lycoming. Take an old fashioned hairpin with the longer end sharpened to a chisel point. You can dislodge the grunge from the insulator by carefully  scratching it with the sharpened hairpin. Remember also plugs should be at the right tension or they overheat and always use an anti seize. on the threads.

    Some carbs are set very rich at idle and long taxi periods will soot the motor.( Carbon, Not lead this time.). You CAN lean them but make it so they are nearly too lean to run and IF you forget to richen it up it will (usually ) cut out  as you advance the throttle or put a small card on the knob  as a reminder, when you do this. Nev

Edited by facthunter

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Depends on the cause of the fouling - see https://m.aircraftspruce.com/catalog/pdf/tempestplugmaint.pdf

My IO-360 has the fine-wire electrodes on the bottom of the cylinders so the only type of fouling that I'd experience is the "bridged electrode" and cycling the prop pitch generally knocks the deposit off.

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Posted (edited)

  That's what is called whiskering same as occurs sometimes with two strokes. It's a fine thread of carbon forming a bridge across the actual points of the plug.. It may dislodge  with a bit of "action" but sometimes it doesn't , but you can flick it off with a gumleaf.  It's that delicate. Nev

Edited by facthunter
amended.

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20 minutes ago, Jaba-who said:

I suspect it was, in effect,  just leaning it a bit more.

Not sure how it could “shock the plug”. 

 

Carb heat enriches the mixture. I always lean the mixture during warm up taxi  on Lyc 0-320.

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12 hours ago, pmccarthy said:

Today I was stuck in the middle of South Australia with a fouled plug. The right mag had been running rough for months, but the drop was not outside limits. Today it nearly shook the engine off its mounts.

 

i tried running it lean for a few minutes, no go. It’s a Lycoming 0360. I rang a mate who is a LAME and he said do that again, but this time pull in carb heat to shock the plug. I did (a few times) and it worked. Smooth running on either mag. This may be common knowledge but somehow I had missed the briefing, and was looking to spend an unplanned night in a strange town. 

 

I had had a spare plug on board, but no spanner. Found out a plumbing tube spanner will fit, from a hardware store. Fortunately that was plan B and not needed.

 

PAX are happy that the delay was only an hour. So my messages are:

 

know how to clear a fouled plug (I thought I did but didn’t)

if you carry a spare plug, also carry a tube spanner to fit.

 

a few years ago I had a flat tyre and that taught me to carry all the tools needed to change one. A spare anything is no use if you can’t change it.

 

Happy New Year.

 

 

      Any EGT indication ? ...... Bob 

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EGT was normal for the 3.5 hour flight before this happened. Then I tried running at 2000rpm as lean as I could, maximum EGT, which didn't help. Did it several times. Then doing that with pulling carb heat fixed it. My friend says the sudden enrichment shocks the plug and makes the deposit fall off. Anyway, it works.

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You can identify which mag is involved with a plug not firing. It will be the mag. that is working when the misfire is happening. Then the EGT will be low on the actual cylinder. So for example if the left mag is working during the misfire and No 3 cylinder has a low EGT it will be No 3 plug fired by the left mag, most likely the top plug.

I have used this method when I had a misfire on the second engine run in my RV, It told me which plug to clean.

To avoid the problem I always taxi on a very lean mixture. Keep it so lean that it will misfire like mad if you apply full throttle and you will not have a failure at take off.

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Thanks guys great topic never to old or smart to learn new tricks !!:thumb up:

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I do exactly that Yenn with my IO 360. taxi lean then richen up just before applying power. Few years ago I experienced misfiring on two occasions, both were fixed by running up, leaning while alternating between mags, never tried intake heat. since then I taxi lean and haven't had a problem.

Edited by Steve L

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