Why iridium plugs are so expensive

[MB65E]

Ahh, yes .032. I just had a surefly fail its internal lighting/timing test during an annual. It was supplied with a new lycoming PN. Lycoming rebrands the surefly with their own label and then seals the dipswitch plug with some serious thread lock. There were not in stock at Lycoming. Ordered a new one from Lycoming. They sent the wrong dash number. Ran like crap. Ended up ordering a new surefly from Spruce and setting the correct dip switch. Funny thing is the surefly and the lycoming(surefly) had different dip switch settings. Nice people still at surefly but they are legally bound not to release info on the lycoming line.

-Matt

[PT20J]

12 minutes ago, MB65E said:

Ahh, yes .032. I just had a surefly fail its internal lighting/timing test during an annual. It was supplied with a new lycoming PN. Lycoming rebrands the surefly with their own label and then seals the dipswitch plug with some serious thread lock. There were not in stock at Lycoming. Ordered a new one from Lycoming. They sent the wrong dash number. Ran like crap. Ended up ordering a new surefly from Spruce and setting the correct dip switch. Funny thing is the surefly and the lycoming(surefly) had different dip switch settings. Nice people still at surefly but they are legally bound not to release info on the lycoming line.

-Matt

The Lycoming EIS is fixed timing only. Did you set your Surefly for variable timing? That would account for the DIP switch differences.

You can check with the experimental sites about how they set their plug gaps. The last time I talked to Surefly about it, they had some legal concerns about recommending wider gaps on certified airplanes. 

A wider gap would allow the voltage to build higher and result in a stronger spark which might improve combustion efficiency slightly. But, probably not by much. If it runs well, I wouldn’t mess with it.

If you do decide to widen the gaps, be very careful not to put any side load on the center electrode. It is very easy to stress the center insulator, and if it breaks later you can get a preignition event that will destroy a cylinder if you don’t catch it and reduce power quickly enough.

[John Mininger]

15 minutes ago, PT20J said:

The Lycoming EIS is fixed timing only. Did you set your Surefly for variable timing? That would account for the DIP switch differences.

You can check with the experimental sites about how they set their plug gaps. The last time I talked to Surefly about it, they had some legal concerns about recommending wider gaps on certified airplanes. 

A wider gap would allow the voltage to build higher and result in a stronger spark which might improve combustion efficiency slightly. But, probably not by much. If it runs well, I wouldn’t mess with it.

If you do decide to widen the gaps, be very careful not to put any side load on the center electrode. It is very easy to stress the center insulator, and if it breaks later you can get a preignition event that will destroy a cylinder if you don’t catch it and reduce power quickly enough.

On a little bit of a sidenote, I remember Mike Busch saying one time that one of his clients had a pre-ignition event. It turned out the electrodes on one of the plugs heated up and became red-hot, because there wasn’t sufficient heat transfer to the head, because the plug had not been torqued correctly.

Turned out it was only finger tight.

[PT20J]

There was also a problem with some Champion massives after the change to the molded-in resistor to eliminate the high resistance issues with the old removable resistor design. A change was made to eliminate the cement between the center electrode and the insulator and some plugs had enough of a gap there that combustion gasses could get in and the pressure would crack the center electrode. I don't know if that got fixed or not, but after I discovered two broken center insulators, I replaced the Champions (which came with the rebuilt engine from Lycoming) with Tempest plugs. 

[skydvrboy]

A related question, is it common for relatively new plugs to fail the resistance test?  Reason I ask, my mechanic replaced all 8 of my plugs at the last annual.  This year, only 120 hours later, three failed the resistance test and were replaced.  He said he's seeing this a lot lately in the various planes he maintains.  Says if they pass the first year they seem to go a long time, but many fail in the first year. 

That seems odd to me and makes me wonder if his tester is faulty.  I asked what resistance value he is using as pass fail and he said he didn't know, he just put them in the tester and it either shows a green light or it doesn't.  That really surprised me because on most things he knows all the when, why, and how rather than just a pass/fail without knowing why.

If it matters, these were Tempest UREM40E's.

[Hank]

@skydvrboy, no idea what his tester uses as Pass / Fail criteria, but I've always heard 5000 ohms. A simple multimeter with two probes will show you the actual resistance, then you decide if it's too high. No need for a fancy tester with lights and what not, especially if you don't know how it works.

[EricJ]

19 minutes ago, Hank said:

@skydvrboy, no idea what his tester uses as Pass / Fail criteria, but I've always heard 5000 ohms. A simple multimeter with two probes will show you the actual resistance, then you decide if it's too high. No need for a fancy tester with lights and what not, especially if you don't know how it works.

Yes, anything greater than 5k Ohms is a fail. 

BTW, Tempest says they'll warrant plugs over 5k Ohms if the gap and ceramic are still good. 

[EricJ]

52 minutes ago, skydvrboy said:

A related question, is it common for relatively new plugs to fail the resistance test?  Reason I ask, my mechanic replaced all 8 of my plugs at the last annual.  This year, only 120 hours later, three failed the resistance test and were replaced.  He said he's seeing this a lot lately in the various planes he maintains.  Says if they pass the first year they seem to go a long time, but many fail in the first year. 

That seems odd to me and makes me wonder if his tester is faulty.  I asked what resistance value he is using as pass fail and he said he didn't know, he just put them in the tester and it either shows a green light or it doesn't.  That really surprised me because on most things he knows all the when, why, and how rather than just a pass/fail without knowing why.

If it matters, these were Tempest UREM40E's.

Get your A&P to save any "failed" plugs and test them with a multimeter.   Anything over 5k Ohms is failure, but less is considered good.   At our last IA seminar the Tempest rep said they warrant plugs over 5k Ohms if the gap and ceramic are still good.

[PT20J]

I’ve found that after the plugs have been in use that it is more difficult to get a good connection to the firing end with a multimeter probe. I have the best luck pressing the probe tip tightly in the gap between the center and a ground electrode.

[hubcap]

I have been running massives in Myrtle since I purchased her 4 years ago and almost 500 hours. I had all the plugs replaced at the last annual after a little over 800 hours. I have absolutely zero complaints. Starts on the 2nd or 3rd blade when cold and will run LOP so smoothly at 9.8gph that I have never felt the need to even try fine wires.

[PT20J]

1 hour ago, skydvrboy said:

A related question, is it common for relatively new plugs to fail the resistance test?  Reason I ask, my mechanic replaced all 8 of my plugs at the last annual.  This year, only 120 hours later, three failed the resistance test and were replaced.  He said he's seeing this a lot lately in the various planes he maintains.  Says if they pass the first year they seem to go a long time, but many fail in the first year. 

That seems odd to me and makes me wonder if his tester is faulty.  I asked what resistance value he is using as pass fail and he said he didn't know, he just put them in the tester and it either shows a green light or it doesn't.  That really surprised me because on most things he knows all the when, why, and how rather than just a pass/fail without knowing why.

If it matters, these were Tempest UREM40E's.

I would expect high resistance failures of either Tempest or current production Champion plugs to be rare. The problem was with older Champion plugs that had the removable resistor. Champion now has a design similar to Tempest. If your mechanic is having this many failures, I would suspect his test rig or method.

[skydvrboy]

2 hours ago, EricJ said:

Get your A&P to save any "failed" plugs and test them with a multimeter. 

Unfortunately, they have already been thrown away.

[A64Pilot]

On 3/25/2024 at 2:59 PM, hubcap said:

I have been running massives in Myrtle since I purchased her 4 years ago and almost 500 hours. I had all the plugs replaced at the last annual after a little over 800 hours. I have absolutely zero complaints. Starts on the 2nd or 3rd blade when cold and will run LOP so smoothly at 9.8gph that I have never felt the need to even try fine wires.

As with a great many things, “better” very often exists, just the difference is often slight, difficult to quantify and frankly impossible to justify as a money savings measure.

Take tires as an example.

However many do feel better with only using the “best” for their airplane, car or whatever, and there is real value in that.

[hubcap]

5 hours ago, A64Pilot said:

As with a great many things, “better” very often exists, just the difference is often slight, difficult to quantify and frankly impossible to justify as a money savings measure.

Take tires as an example.

However many do feel better with only using the “best” for their airplane, car or whatever, and there is real value in that.

Better in this case, may or may not actually exist. If you think something is better, it IS better for you, I get that. Perception = reality.

I try to make my decisions based on data.

Assuming fine wires are "better" what's the pay back? Increased fuel economy? More power? Better starts?

Not being argumentative, just curious. Again, I am perfectly happy with my current performance, but I do try to use what I believe is "best".

[PT20J]

24 minutes ago, hubcap said:

Better in this case, may or may not actually exist. If you think something is better, it IS better for you, I get that. Perception = reality.

I try to make my decisions based on data.

Assuming fine wires are "better" what's the pay back? Increased fuel economy? More power? Better starts?

Not being argumentative, just curious. Again, I am perfectly happy with my current performance, but I do try to use what I believe is "best".

There is a lot of mystique around fine wire plugs, but the physics is actually pretty simple. Compared to standard massive electrode plugs, the electrodes of fine wire plugs are made of a much harder material with a higher melting point, they are smaller, and they protrude farther into the combustion chamber. The harder material and higher melting point is what causes them to last longer and not require frequent gap adjustment. The smaller electrodes run hotter to better burn off deposits and this can help with engines that are prone to plug fouling. The electrodes protruding farther into the combustion chamber make it easier for the spark to contact and ignite the mixture which can help with starting and also running with weak (LOP) fuel/air mixtures. 

The extended electrode BY plugs were developed to be less prone to fouling and are much less expensive if your engine is approved for them. But, you don’t get the longevity and reduced maintenance benefits of the iridium plugs. 

[Will.iam]

3 hours ago, hubcap said:

Better in this case, may or may not actually exist. If you think something is better, it IS better for you, I get that. Perception = reality.

I try to make my decisions based on data.

Assuming fine wires are "better" what's the pay back? Increased fuel economy? More power? Better starts?

Not being argumentative, just curious. Again, I am perfectly happy with my current performance, but I do try to use what I believe is "best".

My airplane when I got it had champion spark plugs and even though it ran fine I.  E. 15 to 20 degrees LOP.  One day I ran across the info that spark plugs should have 5k ohms or less so on my next oil change I took the plugs out to measure them on my voltmeter and they were all over the place with only 3 plugs passing the >5k ohms test all the rest were over the 5k limit but 2 plugs had over 100k ohms and one plug took the top honors of 2 million ohms! I could not believe that one was even working! I bought all fine wire and measured them before putting them in and all were >1k ohms. I did see my fuel flow reduce 0.5 gal per hour flow rate for the same speed and temperatures on my cht’s now how much of that was due to fine wire and how much of that was due to bad plugs I don’t know (my guess would be 30% fine wire and 70% getting rid of bad plugs and having a more balanced set) but I can now go LOP to 90 degrees before getting rough. 

[Hank]

What do fine wire plugs cost? The last massive I bought just a few years ago were $30 each, versus a set of 6 for my Ford Ranger at $17 and some change.

I recall discussions that fine wire plugs last ~2000 hours, while massives are ballparked at ~500 hours, but fine wire plugs cost much more than four times massive plugs, so there needs to be some justification for the (significant) extra expense; a half gallon per hour for 2000 hours is 1000 gallons of avgas, which should be several times the cost of 8 fine wire plugs.

[Ragsf15e]

23 minutes ago, Hank said:

What do fine wire plugs cost? The last massive I bought just a few years ago were $30 each, versus a set of 6 for my Ford Ranger at $17 and some change.

I recall discussions that fine wire plugs last ~2000 hours, while massives are ballparked at ~500 hours, but fine wire plugs cost much more than four times massive plugs, so there needs to be some justification for the (significant) extra expense; a half gallon per hour for 2000 hours is 1000 gallons of avgas, which should be several times the cost of 8 fine wire plugs.

They’re about $135 each.  I use them.  Engine runs great!  But maybe I shouldn’t use them?  Heck I dont know, but it’s hard to change away from a good thing.

[MikeOH]

Guess I'm a certified CB!  When my massives started to look football shaped (still ran great LOP, no fouling) I just replaced them with new Champion massives.  I just couldn't justify that kind of cost difference to myself without some hard evidence; ads/marketing stuff/SGOTIs not sufficient

[N201MKTurbo]

The football shape thing is just a conspiracy  to sell more spark plugs.

If you can still gap them and the side electrodes are not so thin that they could cause preignition, why replace them?

[A64Pilot]

On 3/27/2024 at 1:26 PM, hubcap said:

Better in this case, may or may not actually exist. If you think something is better, it IS better for you, I get that. Perception = reality.

I try to make my decisions based on data.

Assuming fine wires are "better" what's the pay back? Increased fuel economy? More power? Better starts?

Not being argumentative, just curious. Again, I am perfectly happy with my current performance, but I do try to use what I believe is "best".

They do work better, if your mag(s) are weak they will make the engine start easier. Whether they save any fuel or not is arguable, they wouldn’t on my engine as it will run smoothly way more LOP than optimal with massives. IF and that’s a big if, but if treated well, they will last the life of the engine, at least to TBO any way.

When I ran them I would only dig out any clinkers with a dental pick and never clean them with any kind of abrasive blast. I never had any problem with them, but in truth I’ve never had any issues with plugs really, but until very recently I removed, cleaned and rotated them at every oil change and maybe that’s why I’ve never had a fouled plug?

I see them as being similar to tires. I doubt many wouldn’t say that Goodyear flight custom III tires aren’t better than say an Airhawk, but are they worth three times the price?

Not to me the Airhawks work just fine from what I can tell.