lifetime of Tempest massive spark plug

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lucius

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7 out of 12 Tempest massive spark plugs had to be replaced after 500 hours on my IO-540 during my annual, because they were out of spec. See picture of one out of spec plug.

What is the usual lifetime of a Tempest massive spark plug? I was under the believe that they last more than 1000 hours, and was surprised that 7 out of 12 had to be replaced.

Thank you.
 

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OP ... you are confusing fine wires. If you got 500 before they failed or footballed out, you did just fine. Replace with fine wires.
 
I put 700 on my Tempest massives, but I run LOP, normally aspirated and generally 2500 or less. I think they would have gone 1000, easy.
I would have just regap the one you took a picture of.

Tom
 
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MooneyDriver78 said:
I put 700 on my Tempest massives, but I run LOP, normally aspirated and generally 2500 or less. I think they would have gone 1000, easy.


Tom
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I put 150 on a set and most of them were staring to football. Still ran fine, but I pulled to finish my GAMIjector project. Boy what a difference! 20 deg deeper lop and smooth! Worth every penny.
 
Unit74 said:
I put 150 on a set and most of them were staring to football. Still ran fine, but I pulled to finish my GAMIjector project. Boy what a difference! 20 deg deeper lop and smooth! Worth every penny.
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They may football, but they are still good if more than 50%.
Clean and regap them.


Tom
 
MooneyDriver78 said:
They may football, but they are still good if more than 50%.
Clean and regap them.


Tom
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Many plugs will still “pass” all the typical tests yet as they age they will not perform. I just replaced a set that weren’t worn out because I could no longer get the engine to run LOP like it once did. With new plugs it went right back to acting normal. Also, if they need cleaning there is probably something wrong causing it that should be addressed.
 
Thank you. Out of curiosity: How would a spark plug refurbisher (if something like this exists) physically change the center electrode from football to soccerball? It would require adding material, which seems difficult to impossible and not worth the time and effort.
 
Doug Reid said:
Did you use a wear gage ?
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Mechanic did during annual and said that they are out of spec. I found the references that confirmed that 500 hours is expected lifetime for non-fine wire. LOP ops should be unrelated, since not affecting wear of electrode. I am operating slightly LOP as well (not deep LOP since less efficient for IO540).
 
lucius said:
How would a spark plug refurbisher (if something like this exists) physically change the center electrode from football to soccerball? It would require adding material, which seems difficult to impossible and not worth the time and effort.
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They don't. They clean them up, test them - and the buyer uses the remaining life of the plug.
A lot of plugs are needlessly pulled early.
(I do understand and respect the concept of anticipatory maintenance to avoid the dreaded aog' perhaps that is the risk of being pro-Busch on these things.)
 
The ones I got at 1300 hours lasted almost exactly 500 hours before they were out of spec. Until then, they were cleaned and tested at each annual inspection. If I had known the engine would still be fine at 1800 hours I would have gotten fine wires, but I’m not complaining.
 
That plug looks like the set hasn't been rotated. The center electrode has all the wear.
 
Don't forget to test the resistance. Normal plugs should be around 1200-1500 Ohms. Anything above 5000 is considered toast and will eventually take out your magneto coil.
 
I just changed mine out at around 900 hours because several would ‘almost’ fit into the no-go check tool. They still ran fine and passed in the bomb box but they were close enough to the wear limits that I didn’t want to push it.

Gary
 
@Raymo, what would that look like on the coil, burn marks to the point of wearing thru, or perhaps a crack? I was having some electrical issues last year and curious. I run REM37BYs now but regardless of brand they all start 'footballing' within a few hundred hours.
 
lucius said:
7 out of 12 Tempest massive spark plugs had to be replaced after 500 hours on my IO-540 during my annual, because they were out of spec. See picture of one out of spec plug.

What is the usual lifetime of a Tempest massive spark plug? I was under the believe that they last more than 1000 hours, and was surprised that 7 out of 12 had to be replaced.

Thank you.
Click to expand...

What "spec" is it out of? Ohm, .022 wire passes through the gap?
 
Timbeck2 said:
What "spec" is it out of? Ohm, .022 wire passes through the gap?
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This one here:

12-00791.jpg


That hole at the bottom is a calibrated diameter. If the plug's business end fits in there after the gap has been set, it has become too eroded. Normally, plug sets are rotated at each cleaning so that the erosion is distributed between the center and side electrodes. The OP's plug in his first post shows the center electrode worn, and the side electrodes like new, which is why I suggested that the set hadn't been rotated.

A magneto has an alternating-current generator built into it. Its design means that the first plug gets a positive spark (spark jumps from side to center) and the next gets a negative (center to side), the third positive again and so on. The negative electrode suffers most, so rotating the plugs from positive-sparking positions to negative-sparking positions evens out the wear so that one electrode doesn't wear out quickly while the other doesn't wear much at all.
 
Dan Thomas said:
This one here:

12-00791.jpg


That hole at the bottom is a calibrated diameter. If the plug's business end fits in there after the gap has been set, it has become too eroded. Normally, plug sets are rotated at each cleaning so that the erosion is distributed between the center and side electrodes. The OP's plug in his first post shows the center electrode worn, and the side electrodes like new, which is why I suggested that the set hadn't been rotated.

A magneto has an alternating-current generator built into it. Its design means that the first plug gets a positive spark (spark jumps from side to center) and the next gets a negative (center to side), the third positive again and so on. The negative electrode suffers most, so rotating the plugs from positive-sparking positions to negative-sparking positions evens out the wear so that one electrode doesn't wear out quickly while the other doesn't wear much at all.
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In additon, there will also be the capacitance difference due to differing ignition wire lengths between the magneto and each plug. That's why the correct rotation to even out the electrode erosion is a bit more elaborate than a simple swapping of lower and upper plugs on the same cylinder:

198595_spark_plug_rotation_diagrams.jpg
 
This Tempest fine wire only made it 100 hours
 

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Dan Thomas said:
This one here:

12-00791.jpg


That hole at the bottom is a calibrated diameter. If the plug's business end fits in there after the gap has been set, it has become too eroded. Normally, plug sets are rotated at each cleaning so that the erosion is distributed between the center and side electrodes. The OP's plug in his first post shows the center electrode worn, and the side electrodes like new, which is why I suggested that the set hadn't been rotated.

A magneto has an alternating-current generator built into it. Its design means that the first plug gets a positive spark (spark jumps from side to center) and the next gets a negative (center to side), the third positive again and so on. The negative electrode suffers most, so rotating the plugs from positive-sparking positions to negative-sparking positions evens out the wear so that one electrode doesn't wear out quickly while the other doesn't wear much at all.
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Question,, How did you determine that was the spec that the plug failed?
 
Dan, Also failed to tell us that his theory of where the spark jumps only works on 4 cylinder engines running a 2 pole magneto.
6 cylinder engines running a 2 pole mag does it automatically, plus how would his theory apply to a 9 cylinder P&W 985?
 
yetti said:
This Tempest fine wire only made it 100 hours
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How fast did Tempest get you a new one out and pay for the shipping back for the old plug so they can QA it??
 
Unit74 said:
How fast did Tempest get you a new one out and pay for the shipping back for the old plug so they can QA it??
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Pretty quick after a delay on my side. I replaced it with a massive Champion to get home. Never got the QA
 
They didn't ask for it back to look at it? Odd for them.....
 
Tom-D said:
Dan, Also failed to tell us that his theory of where the spark jumps only works on 4 cylinder engines running a 2 pole magneto.
6 cylinder engines running a 2 pole mag does it automatically, plus how would his theory apply to a 9 cylinder P&W 985?
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The four-banger has its magneto driven at a 1:1 ratio to the crankshaft so that each plug gets the same polarity in every firing cycle. The six-cylinder's magnetos are geared to the crank at a 1.5:1 ratio so that for each two revolutions of the crank (one complete firing cycle) the magneto turns three times. That way, each plug still gets the same polarity in every firing cycle, same as the four-cylinder engine, since the magneto's rotor starts in the same position at the beginning of the firing sequence.

Lycoming, on pages 88 and 89 of their Key Reprints, recommends rotating the plug set in all their engines. And in their Direct Drive Overhaul Manual they show the 1:1 drive ratio in the fours and the 1.5:1 in the sixes:

upload_2019-3-21_8-15-36.png

Slick's magneto manual (L1363F) has this to say:

A two-lobe cam and two-pole rotating magnet assembly are
used to generate magnetic flux and trigger the high tension
spark energy. Four-cylinder magnetos are driven at engine
speed and produce four sparks through 720 degrees of
crankshaft rotation. Six-cylinder magnetos are driven at one
and one half times engine speed and produce six sparks
through 720 degrees of engine crankshaft rotation.

Now, a radial's odd number of cylinders is indeed a different animal. But how many of us here have worked on, or flown, a radial?
 
Tom-D said:
IGN-51.pdf

page 9
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That four-pole rotor must be for a radial. If the six-cylinder's mag had four poles, and turned at 1.5 times crankshaft speed, it would generate six sparks per crankshaft revolution, or 12 sparks per full firing sequence. Not much use on a six-banger.
 
Dan Thomas said:
That four-pole rotor must be for a radial. If the six-cylinder's mag had four poles, and turned at 1.5 times crankshaft speed, it would generate six sparks per crankshaft revolution, or 12 sparks per full firing sequence. Not much use on a six-banger.
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Typical Bendix.
 
Here is mine after 440.
 

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iflyvfr said:
@Raymo, what would that look like on the coil, burn marks to the point of wearing thru, or perhaps a crack? I was having some electrical issues last year and curious. I run REM37BYs now but regardless of brand they all start 'footballing' within a few hundred hours.
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Cracks, from I've been told by mag peeps.
 
yetti said:
This Tempest fine wire only made it 100 hours
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Were they cleaned with small sand or glass blasting media? Tempest says it is a NO-NO and will cause early failure. Lots of good info in the linked PDF.

EDIT: Tempest allows glass beads, per the aforementioned PDF, but require a minimum size to avoid erosion of the enamel that holds the center electrode.
 
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Any abrasive that's too big will wedge in there like that. There are many sizes of glass bead, and the fine stuff is actually easier on the plug that the silicon carbide grit sold for cleaning plugs. The glass is round, and shatters into smaller bits as it's used. The silicon carbide is extremely hard and angular, and cuts the metal away far more quickly. And if there's any of that stuff in the plug when the plug is reinstalled, it will score the cylinder far worse than the glass.

I have many years of shop experience outside of aviation, and used glass beads of various grades as well as ground copper slag, also a hard and angular material. I only used the silicon carbide in plug cleaners, and found that it eroded the plugs faster. I would take fine glass any day, and the good mechanic will use a magnifier and light to check the plug wells before he reinstalls them. I kept 4X reading glasses around for that.
 
Dan Thomas said:
Any abrasive that's too big will wedge in there like that. There are many sizes of glass bead, and the fine stuff is actually easier on the plug that the silicon carbide grit sold for cleaning plugs. The glass is round, and shatters into smaller bits as it's used. The silicon carbide is extremely hard and angular, and cuts the metal away far more quickly. And if there's any of that stuff in the plug when the plug is reinstalled, it will score the cylinder far worse than the glass.
I have many years of shop experience outside of aviation, and used glass beads of various grades as well as ground copper slag, also a hard and angular material. I only used the silicon carbide in plug cleaners, and found that it eroded the plugs faster. I would take fine glass any day, and the good mechanic will use a magnifier and light to check the plug wells before he reinstalls them. I kept 4X reading glasses around for that.
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On a related note, what do you guys think of using a bench grinder with a wire wheel to clean the electrodes? Sounds a lot easier than a brass toothbrush or would I be destroying them?
 
iflyvfr said:
On a related note, what do you guys think of using a bench grinder with a wire wheel to clean the electrodes? Sounds a lot easier than a brass toothbrush or would I be destroying them?
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That isn't recommended at all. Champion doesn't like it. The wire wire wheel smears the electrode metal, and can leave sharp little edges that get hot and burn away quickly. They also make gap readings difficult.

And it can't get the deposits out of the plug well anyway. Some mechanics just use a fine pick to remove the worst of the deposits. A dental pick that uses a hard, fine wire is good for that.

Champion's manual. Plug reconditioning starts on page 13. https://www.google.com/url?sa=t&rct...Aug20141.pdf&usg=AOvVaw3oBWzEafY702m9_lNIQ8LU
 
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