Spark plug maintenance?

gkainz

gkainz

Final Approach
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Greg Kainz
Started the annual on our '83 Piper Dakota this weekend - cleaning and gapping the spark plugs (Tempest Massive Electrodes) and noticed that the ground electrodes have "fangs" or tangs protruding on the leading and trailing edge of each ... is this "normal"? A result of plug wear? Fixable or ignorable?
 
gkainz said:
Started the annual on our '83 Piper Dakota this weekend - cleaning and gapping the spark plugs (Tempest Massive Electrodes) and noticed that the ground electrodes have "fangs" or tangs protruding on the leading and trailing edge of each ... is this "normal"? A result of plug wear? Fixable or ignorable?
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Doesn't sound "normal" if they are metal. If it's how I'm imagining it from your description they might be capable of pre-igniting the fuel air mixture under the right conditions and that would be bad.

Can they be "knocked off"?

How about a picture or two?
 
Here is a clean set in the gap tool. Interested to see the 'fangs' you speak of.

gap+tool+1.jpg
 
reverting back to kindergarten drawing tools, the birdseye view of the electrodes look something like this ... (this could be embarrassing ... if so, will definitely go get a photo tonight).

best description might be to imagine the ground electrodes as having little "staple-like legs" pointing towards the center electrode on either end...maybe a couple of thousanths long ... enough to be visible to the eye and snag between the .014 and .018 feelers
 

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If its legit when was the last time the plugs were rotated between firing positions?
 
lol - since the annual commenced yesterday, this is not an April Fool's Day joke.

We rotate plugs top to bottom, front to back every annual minimum (not sure if more often than that), and we flew this plane about 300 hours last year. However, I think this plane got a new set of plugs somewhere between now and last annual.

Edit - BTW, my crude drawing is ABSOLUTELY NOT TO SCALE!!!! :D
 
I would find out how long they had been in that position. My money is on wear. By chance did you check the gap before setting it? Perhaps the electrodes wore to an approximately equal distance across the surface.
 
I did check the gaps on all the plugs and they all were slightly larger than .018, except for the leading and trailing edges, which just passed the .014 gauge.

The dilemma is to gap the narrowest part or the widest part? Neither option sounds right to me.
 
Odd for sure. But looks like wear either way. Do you have a total time on the plugs?
 
I have seen that. It can be a result of sloppy manufacturing, or of erosion. In your case, since you say your plugs were replaced not long ago, I'd suspect that the machinery that stamps out those electrodes before they're welded to the plug body is making a sloppy job of it and leaving a smeared cut on the edges. That sharp tang can glow and cause preignition.

I sure do miss Auburn plugs. They were the last truly airworthy sparkplugs ever made. All the current plugs might be legally airworthy, but they are of rotten quality. Perhaps the fine-wire plugs are better...

Dan
 
Dan Thomas said:
I have seen that. It can be a result of sloppy manufacturing, or of erosion. In your case, since you say your plugs were replaced not long ago, I'd suspect that the machinery that stamps out those electrodes before they're welded to the plug body is making a sloppy job of it and leaving a smeared cut on the edges. That sharp tang can glow and cause preignition.

I sure do miss Auburn plugs. They were the last truly airworthy sparkplugs ever made. All the current plugs might be legally airworthy, but they are of rotten quality. Perhaps the fine-wire plugs are better...

Dan
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.

I respectfullly disagree...:yes:.

The reason people are paying 25 -100 dollars a plug is they are under the impression FAA certified aircraft parts are top quality and go through multiple quality control checks and should be PERFECT right out of the box..... This is no different then the debate we all had a few weeks ago on Kelly Aerospace junk carbs.... As Tom and other A&P's said... Everyone needs to tell the FSDO /FAA or someone in charge of the defect using Service and difficulty report , or whatever they called that form....

This stuff in the MAIN reason I went with an auto conversion, as parts are almost always higher quality then FAA Approved crap... And way cheaper too.:yes::D;)
 
N801BH said:
.

I respectfullly disagree...:yes:.

The reason people are paying 25 -100 dollars a plug is they are under the impression FAA certified aircraft parts are top quality and go through multiple quality control checks and should be PERFECT right out of the box..... This is no different then the debate we all had a few weeks ago on Kelly Aerospace junk carbs.... As Tom and other A&P's said... Everyone needs to tell the FSDO /FAA or someone in charge of the defect using Service and difficulty report , or whatever they called that form....

This stuff in the MAIN reason I went with an auto conversion, as parts are almost always higher quality then FAA Approved crap... And way cheaper too.:yes::D;)
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Many ignition systems available for experimentals use auto spark plugs also. They have a much hotter spark and advance the timing for better fuel economy. Throw the plugs away after 200 hours. :dunno:

The major problem with auto conversions is adding turn signals and brake lights to the plane. Confuses ground crews. ;)
 
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Geico266 said:
.......
The major problem with auto conversions is adding turn signals and brake lights to the plane. Confuses ground crews. ;)
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:rofl::lol:...

My biggest problem is keeping the white walls on the tires clean.. For that reason I installed curb feelers....;)
 
Dean V said:
My experiance is the 235hp rated Lyc O-540s are tough on spark plugs. Yours are worn out.
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And what did you base that opinion upon ?
 
didn't make it to the hangar last night - hope to get there tonight and snap a few photos.
 
Not the best pics as the focus didn't center on the electrodes with the iPhone, but here's a sample

a5agu5un.jpg


una6ymup.jpg
 
They look normal. To even out the wear pattern over time the proper way to rotate plugs is top to bottom and move to the next cylinder in the firing order. In 4 cylinder Lycomings the order is 1-3-2-4
 
Silvaire said:
They look normal.

:yeahthat:


To even out the wear pattern over time the proper way to rotate plugs is top to bottom and move to the next cylinder in the firing order. In 4 cylinder Lycomings the order is 1-3-2-4
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That's one of the theories that work on paper but really it saves about 10 minutes on the life of the plug.not worth doing.
 
Well you're only going to rotate the plugs when they are out for maintenance, you're not going to remove the plugs solely for the purpose of rotation so there is no "time" involved in the process. If the plugs are not rotated throughout their life half of them will have fangs and the other half will have elliptical center electrodes. If they are rotated properly they will last longer. How much longer I don't know. I rotate them, if you don't want to then don't.
 
Silvaire said:
Well you're only going to rotate the plugs when they are out for maintenance, you're not going to remove the plugs solely for the purpose of rotation so there is no "time" involved in the process. If the plugs are not rotated throughout their life half of them will have fangs and the other half will have elliptical center electrodes. If they are rotated properly they will last longer. How much longer I don't know. I rotate them, if you don't want to then don't.
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If you do, If you don't, the plug will last about 500 hours.
 
We rotate top to bottom and move (but not sure if we cycle down the cylinders following firing order).
I will have to check how often. We do "team efforts" on our annuals so this is my first time with plugs. I also want to find out how many hours on these plugs both total time and in-place hours.
I noted some elliptical center electrodes and some of the protrusions on the ground electrodes - some more noticeable than others.
One comment by our maintenance officer was these plugs were considerably cleaner (less lead) than he expected.
 
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gkainz said:
We rotate top to bottom and move (but not sure if we cycle down the cylinders following firing order).
I will have to check how often. We do "team efforts" on our annuals so this is my first time with plugs. I also want to find out how many hours on these plugs both total time and in-place hours.
I noted some elliptical center electrodes and some of the protrusions on the ground electrodes - some more noticeable than others.
One comment by our maintenance officer was these plugs were considerably cleaner (less lead) than he expected.
Click to expand...

They say proper spark plug rotation can double the life of the plugs. This may be just an OWT. YMMV

http://www.aviationpros.com/article/10387932/why-rotate-spark-plugs

For a six-cylinder engine move plugs:
1T to 6B
2B to 5T
3T to 4B
1B to 6T
2T to 5B
3B to 4T
For a four-cylinder engine move plugs:
1T to 4B
2B to 3T
1B to 4T
2T to 3B
 
bnt83 said:
They say proper spark plug rotation can double the life of the plugs. This may be just an OWT. YMMV

http://www.aviationpros.com/article/10387932/why-rotate-spark-plugs

For a six-cylinder engine move plugs:
1T to 6B
2B to 5T
3T to 4B
1B to 6T
2T to 5B
3B to 4T
For a four-cylinder engine move plugs:
1T to 4B
2B to 3T
1B to 4T
2T to 3B
Click to expand...

Answer this, If a molecule of metal is removed from the electrodes each time the plug fires, Does it really matter if it is removed from the + or the -?

The plug will be re-gapped at the next cleaning and will be removed from service when enough of the electrodes have been lost.
 
Tom-D said:
Answer this, If a molecule of metal is removed from the electrodes each time the plug fires, Does it really matter if it is removed from the + or the -?

The plug will be re-gapped at the next cleaning and will be removed from service when enough of the electrodes have been lost.
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Just what the "experts" say. I don't think it matters.
 
bnt83 said:
Just what the "experts" say. I don't think it matters.
Click to expand...

It matters. When a spark jumps the gap, erosion happens at the electrode where the spark lleaves, which is the negative electrode. Since a magneto is an alternating-current generator, the spark voltages it produces are alternating. If the firing order is 1-3-2-4, for example, 1 and 3 are of one polarity and 2 and 4 are of the other. If we use the plug in the same hole its whole life, one electrode (either the center or the ground) will suffer more and wear to limits sooner than the other one will.

Any welder know that polarity makes a difference to the weld. Some welding rods or wires need positive, some negative. All depends whether we want the filler or the parent metal to melt more.

Dan
 
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Dan Thomas said:
It matters. When a spark jumps the gap, erosion happens at the electrode where the spark lleaves, which is the negative electrode. Since a magneto is an alternating-current generator, the spark voltages it produces are alternating. If the firing order is 1-3-2-4, for example, 1 and 3 are of one polarity and 2 and 4 are of the other. If we use the plug in the same hole its whole life, one electrode (either the center or the ground) will suffer more and wear to limits sooner than the other one will.

Any welder know that polarity makes a difference to the weld. Some welding rods or wires need positive, some negative. All depends whether we want the filler or the parent metal to melt more.

Dan
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I get the reason behind it, but wore out is wore out wether the wear is uniform between the electrodes or if all the wear is in the center or the outer ones...

If 10,000,000 sparks happen on a plug that was rotated it will not look the same but the ammount of wear will essentially be the same as one that wasn't rotated.
 
bnt83 said:
I get the reason behind it, but wore out is wore out wether the wear is uniform between the electrodes or if all the wear is in the center or the outer ones...

If 10,000,000 sparks happen on a plug that was rotated it will not look the same but the ammount of wear will essentially be the same as one that wasn't rotated.
Click to expand...

You can end up with a plug that has a nice fat center electrode and really thin ground electrodes that glow red-hot and start causing preignition, too. That's not a desirable form of wear.

Dan
 
Tom-D said:
Answer this, If a molecule of metal is removed from the electrodes each time the plug fires, Does it really matter if it is removed from the + or the -?
Click to expand...

2300 rpm for 100 hours means 13,800,000 molecules removed from the center electrode. Rotate the plugs as recommended and in the next 100 hours 13,800,000 molecules come off the ground electrodes so, in theory, the plugs would last twice as long when properly rotated. I know that's not true but rotating them does help to keep the wear proportional which makes it a bit easier to set the gaps as they age. I've seen plugs with seriously eroded center electrodes that still pass the GO/NO-GO gauge check but look like you'd want to replace them. I think rotating them does make a difference and really, I don't see any good reason not to.
 
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