Cleaning and gapping spark plugs

Tom-D said:
The best tester you have is the engine. I very very seldom test plugs when I clean them. They were running when you removed them, if all you did was the normal clean, and set gap, Why shouldn't they run when you reinstall them?
Your going to run the engine, and do a mag check, that will tell you if you have a problem.
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Yup. And when the engine starts to act up, especially in an intermittent manner, determining which of the plugs is defective--if it IS a plug--becomes a big hassle. Give me a tester anytime. Ignition is responsible for he vast majority of engine misbehaviors, so ignition diagnostic tools make sense to me.

Of course, many folks will fool with the fuel system for three weeks until they figure out that something else might be haywire.
 
Dan Thomas said:
Yup. And when the engine starts to act up, especially in an intermittent manner, determining which of the plugs is defective--if it IS a plug--becomes a big hassle. Give me a tester anytime. Ignition is responsible for he vast majority of engine misbehaviors, so ignition diagnostic tools make sense to me.

Of course, many folks will fool with the fuel system for three weeks until they figure out that something else might be haywire.
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Proper trouble shooting with a cold cylinder test will get it every time.
 
Seriously, I wouldn't bother screwing around with plugs when those ladies that I referred to earlier do the best job that can be done and test them beyond most shop capabilities for peanuts.
 
Tom-D said:
Proper trouble shooting with a cold cylinder test will get it every time.
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Not when it's intermittent or only does it at higher power settings. Much easier to test those plugs whenever they're out for cleaning; saves much time ($$$) later on. I recently tested a set of plugs, and had eight of the twelve stop arcing at 110 or 120 psi. With some you could hear the arc popping away inside the barrel; there was microscopic cracking in the ceramic that resulted in invisible carbon tracking. The rest just quit because their resistors were being stupid. None of them were Tempests or ACs or Auburns or Unisons, btw. I replaced the works with new Tempests, and the owner commented on the smoothness and extra power of the engine. If we hadn't tested and replaced them he'd have happily flown a sick airplane until it finally failed him.

This is not unusual. I often find sick plugs in airplanes that should have had better maintenance.

And I have encountered testers that are out of calibration. A machine like that either misses bad plugs or calls good plugs bad. The manufacturers of those things have procedures for periodic checking of accuracy; the voltage is adjustable and the gauge should also be checked.

Page 18 of this manual: http://www.championaerospace.com/wp-content/uploads/2015/06/AV6-R-Aug20141.pdf
 
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Dan Thomas said:
Not when it's intermittent or only does it at higher power settings. Much easier to test those plugs whenever they're out for cleaning; saves much time ($$$) later on. I recently tested a set of plugs, and had eight of the twelve stop arcing at 110 or 120 psi. With some you could hear the arc popping away inside the barrel; there was microscopic cracking in the ceramic that resulted in invisible carbon tracking. The rest just quit because their resistors were being stupid. None of them were Tempests or ACs or Auburns or Unisons, btw. I replaced the works with new Tempests, and the owner commented on the smoothness and extra power of the engine. If we hadn't tested and replaced them he'd have happily flown a sick airplane until it finally failed him.

This is not unusual. I often find sick plugs in airplanes that should have had better maintenance.

And I have encountered testers that are out of calibration. A machine like that either misses bad plugs or calls good plugs bad. The manufacturers of those things have procedures for periodic checking of accuracy; the voltage is adjustable and the gauge should also be checked.

Page 18 of this manual: http://www.championaerospace.com/wp-content/uploads/2015/06/AV6-R-Aug20141.pdf
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Well,,, when you allow the plugs to go to a point that all will fail, the cure is obvious.\
 
Dan Thomas said:
That tester is very good at finding the plugs that have failing internal resistors or cracked ceramic insulators; they're the plugs that cause all sorts of rough-running headaches. There are other testers available for a lot less than Champion's.
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That's what I thought too, until I started comparing results of the ohmmeter test to the bomb tester. Ultimately, the meter is much more sensitive and will give you better results. I had almost three dozen (champion) plugs that I ran through the bomb tester and they passed the check. However, when I did the resistance check with a good meter I found that an easy 1/3 of them were rejects. Just for fun, I stuck a screwdriver down the barrel and unscrewed the cap that holds in the resistor (on every reject plug). All of the ones that were rejects were corroded internally.

No, I'm not kidding... ALL of the ones that failed the resistance check were internally corroded... ALL of THEM. Champion has lost this customer forever.

Some people swear by the bomb tester, but I've seen the light. (And I've never had a hard starting plane ever since!)

V/r,

-Dana
 
thomasdr72 said:
That's what I thought too, until I started comparing results of the ohmmeter test to the bomb tester. Ultimately, the meter is much more sensitive and will give you better results. I had almost three dozen (champion) plugs that I ran through the bomb tester and they passed the check. However, when I did the resistance check with a good meter I found that an easy 1/3 of them were rejects. Just for fun, I stuck a screwdriver down the barrel and unscrewed the cap that holds in the resistor (on every reject plug). All of the ones that were rejects were corroded internally.

No, I'm not kidding... ALL of the ones that failed the resistance check were internally corroded... ALL of THEM. Champion has lost this customer forever.

Some people swear by the bomb tester, but I've seen the light. (And I've never had a hard starting plane ever since!)

V/r,

-Dana
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The bomb tester finds the cracked ceramics that the resistance test can't. And I have measured resistors that are far beyond the recommended limits that still spark just fine. I have never seen an internally corroded Champion resistor well, but I have found that if you take out that screw and spring and resistor, from a plug that sparks OK on the tester (a plug worn out by erosion but otherwise still firing), and then put it all back together, it probably won't spark anymore. Same thing with dropping it on the concrete floor. Champion recently changed their resistor setup to the molded-in (monolithic) resistor that Auburn used to use and that Tempest uses. We'll see if it fixes things up.

The bomb tester works because it simulates the compression the plug has to fire in. The ohmmeter can't simulate that. The only thing the bomb tester can't do it test the plug at typical cylinder head temperatures, and sometimes that's a factor.
 
Dan Thomas said:
The bomb tester finds the cracked ceramics that the resistance test can't. And I have measured resistors that are far beyond the recommended limits that still spark just fine. I have never seen an internally corroded Champion resistor well, but I have found that if you take out that screw and spring and resistor, from a plug that sparks OK on the tester (a plug worn out by erosion but otherwise still firing), and then put it all back together, it probably won't spark anymore. Same thing with dropping it on the concrete floor. Champion recently changed their resistor setup to the molded-in (monolithic) resistor that Auburn used to use and that Tempest uses. We'll see if it fixes things up.

The bomb tester works because it simulates the compression the plug has to fire in. The ohmmeter can't simulate that. The only thing the bomb tester can't do it test the plug at typical cylinder head temperatures, and sometimes that's a factor.
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Although I do agree with you that the tester does have some utility, (and I have used it when available) I just can't justify the expense myself... Another possible outcome of high resistance plugs is damage to the magneto internals. The electrical spark is intended to cross a gap at a particular range of resistance. If you get too far outside of those specifications, you eventually come to a point where the current will begin to search for other path(s) to ground. This becomes increasingly likely with normal wear and carbon dust buildup inside your mags. I've seen pics of caps that develop a carbon track that burns through the cap. Not to mention the stress that these issues cause to your primary coil. Plugs are expensive (fine wires especially!) but eventually they all end up in the bin! ;-)

I haven't personally seen a broken insulator in service, but I've definitely dropped a plug or two. The very next place they end up is in the trashcan...

V/r,

-Dana
 
thomasdr72 said:
Although I do agree with you that the tester does have some utility, (and I have used it when available) I just can't justify the expense myself... Another possible outcome of high resistance plugs is damage to the magneto internals. The electrical spark is intended to cross a gap at a particular range of resistance. If you get too far outside of those specifications, you eventually come to a point where the current will begin to search for other path(s) to ground. This becomes increasingly likely with normal wear and carbon dust buildup inside your mags. I've seen pics of caps that develop a carbon track that burns through the cap. Not to mention the stress that these issues cause to your primary coil. Plugs are expensive (fine wires especially!) but eventually they all end up in the bin! ;-)

I haven't personally seen a broken insulator in service, but I've definitely dropped a plug or two. The very next place they end up is in the trashcan...

V/r,

-Dana
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Yeah, a tester is too expensive for a guy doing his own maintenance on one airplane.

Pretty much all magnetos are designed with a means of letting a spark jump to ground in the mag if the plug opens or a lead fails. The high-voltage coil tab is usually positioned a sufficient distance from the metal case so that proper firing isn't shorted, but an open plug lets the spark go to ground to avoid cooking the coil. better to lose one cylinder than all of them.

Carbon tracking is usually a result of letting the mag go too long between inspections and cleanings. Carbon dust from the brush will dust everything and eventually form a path for the spark, and the spark then burns stuff. Once plastic distributor parts begin to burn, more carbon is released to aggravate the process.
 
Dan Thomas said:
Pretty much all magnetos are designed with a means of letting a spark jump to ground in the mag if the plug opens or a lead fails. The high-voltage coil tab is usually positioned a sufficient distance from the metal case so that proper firing isn't shorted, but an open plug lets the spark go to ground to avoid cooking the coil. better to lose one cylinder than all of them.
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Interesting note... I hadn't read that anywhere, but it would make sense! Thanks!
 
Dan Thomas said:
Pretty much all magnetos are designed with a means of letting a spark jump to ground in the mag if the plug opens or a lead fails.
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The high-voltage coil tab is usually positioned a sufficient distance from the metal case so that proper firing isn't shorted,[/QUOTE]
Hardly.
 

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Tom-D said:
Hardly.
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Yeah I don't really believe that either considering the atmospheric pressure inside a mag vs the pressure in a cylinder can vary greatly.

Also, held in your hand and sparking it without a harness on them will show that it will jump one hell of an air gap.
 
When you fly an unpressurized mag too high its seems to me like it just does whatever it wants to and not discharge through a designed safety feature.
 
Tom. You should find and read the Slick and Bendix manuals sometime.
 
bnt83 said:
When you fly an unpressurized mag too high its seems to me like it just does whatever it wants to and not discharge through a designed safety feature.
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Any mag in todays operation will fire normally as high as any non TSIO engine will fly, When you use a TSIO- you run a hose from the intake pressurized point to the mag case and pressurize it too.
 
High altitude cross fire destroys parts internal to the magneto, burning the rotor at a minimum how would an open plug at low altitude be much different?
 
bnt83 said:
High altitude cross fire destroys parts internal to the magneto, burning the rotor at a minimum how would an open plug be much different?
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mine are sealed....but not connected/plumbed to the upper deck as Tom described.
 
Checkout_my_Six said:
mine are sealed....but not connected/plumbed to the upper deck as Tom described.
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IO520 powered 210D can go 20K feet...

The gaps are so large inside the mag I don't see any built in safety feature to prevent damage from an open plug whether on the ground or at 20k feet.
 
Checkout_my_Six said:
mine are sealed....but not connected/plumbed to the upper deck as Tom described.
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The Piper Arrow I serviced with a TSIO-360- did. that's the most resent aircraft that I've noticed it on.
 
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