# When using a mag, How many rotate their spark plugs?

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#### N8053H

##### Well-Known Member
Like the title says. How many rotate their spark plugs in order. Say your firing order is 1234 like my vw. How many will take the number one spark plug and move it to the number two spot and so on, number two in the number three spot ect...

This is not about swapping lower plugs for upper plugs.

Tony

#### TFF

##### Well-Known Member
With a mag verses car style ignition, a magnet is powering the spark directly. A magnet has + and - ends of course. two cylinders will have the electrical generated from the + side and two will be from the - side. So on a 4 cylinder with a mag, lets say the first cylinder gets the +, the next gets shot with -, next with + next with -, and it starts all over. What you see is on the electrodes with one charge will erode the center electrode and one will erode the side ones. Moving them in a systematic rotation gets the erosion to equal out without having to know which plug is really + or -. If you leave a plug in a cylinder it will start to show a distinct erosion pattern. Each cylinder can have its own additions like running hotter or leaner which will add another dimension to plug wear that moving them around will even out. That is the purpose of the fancy plug caddies. A systematic way to help move the plugs around. Think of all the plugs on a 36 cylinder radial.

#### N8053H

##### Well-Known Member
TFF do you rotate your plugs because of this? I am replacing the plugs on my engine at a cost of a small fortune. The plugs looked to never been rotated. The new ones will be rotated once a year no matter the hrs.

Tony

#### N8053H

##### Well-Known Member
I did not post this to show how smart I am. No far from it. I posted this because I do not know squat about aviation anything. So when I went to replace these plugs, REL 37B, I wanted to research what it was I am doing. In doing this I found this info from Champions website. When I noticed that these plugs look to never have been rotated I thought, others too must not know this info. I wanted to share so others who use expensive massive electrode aviation plugs can get the most life from them. These are not cheap. Imagine if you had to replace 8 or 16 or more of these....WOW.

Tony

#### N8053H

##### Well-Known Member
I use these plugs as did the other owner of this airplane because this is a single ignition engine. My 1/2 vw gets the same style plug being fine wire for the same reason. But that engine uses auto plugs and they cost a few bucks each. I keep a couple spare boxes of these. I doubt I will ever keep spare REL 37B spark plugs. Just to expensive to have laying around.

But my point. This is another plus as to a dual ignition engine. I would not be using these expensive plugs. I would still use aviation plugs but not fine wire. The other plugs are half the price of these REL 37B plugs.

Tony

#### Pops

##### Well-Known Member
Log Member
I use the same plugs on my VW engine. At this time they are mostly in the $60+ each but Chief has them for$52 , that is the cheapest I have found the REL 37B plugs . Back in 2007 when I first bought the same plug I paid \$42 each.

#### N8053H

##### Well-Known Member
Pops do you rotate these plugs?

Log Member

#### narfi

##### Well-Known Member
The lycomings and continentals I work on get 500+ hours a year.
I use the random method for rotation.
By this I pull the plugs out at 100hrs look to make sure nothing is worth noting about condition and randomly place them in the tray and then clean and gap them. Then randomly select them to reinstall.

Do this 17-20 times till oh and they all get a chance somewhere.

Often we keep a spare set or two cleaned and gapped on the bench coated with lps or similar to keep them from rusting and just spray them down with cleaner and install in place of what was on the engine. This let's us finish a 100hr faster and we can clean and gap the dirty set when it's slow.

Fine wire certainly saves a lot of labor and time.

#### TFF

##### Well-Known Member
Airplane spark plugs will last 2000 hours if taken care of and not dropped. If dropped, throw away. They are expensive no getting around that, but they are designed to survive the wear. i keep all old plugs when I send an engine back for overhaul; if I find a bad one or drop one, I get used one out of the box. I rotate every 100 hrs or annual. I will do twelve 100hrs a year on just the company aircraft. When you see the same aircraft in that close contact, you can actually see the patterns others have to take for granted on recommendation. Low use aircraft, moving the plugs around is nice, but I doubt you will see any wear pattern without a couple of hundred hours in one spot, but if you dont take them in and out, they can get stuck in the threads. A friend has electrinic ignition on his RV with car plugs; pitches them every year. Overall he probably will spend the same money on plugs over the 2000 hrs, but it does not seem as painful. The spark plug caddies will have the plugs in cylinder order top and bottom. When you go to put them in you advance one plug. #1 top becomes #1 bottom, #1 bottom becomes #2 top, #2 top becomes #2 bottom all around to #4 bottom going into #1 top. Idea is a plug will never live in one position over the 2000 hrs. When you think in terms of 2000 hrs and you will put 150 on in your whole ownership, less usage becomes a factor just as much as usage.

#### N8053H

##### Well-Known Member
Seeing how I only fly single ignition as many experimental do, not all but a lot. More then you see in the GA world anyway. This is not about swapping top for bottom but just rotating them.

I came around to all this not because I like spending money and just wanted a new set of plugs. This engine was getting hard to start. When I purchased this airplane the owner told me he had no idea why it was getting so hard to start. He double checked everything and everything was right on, timing and such.

When looking over the airplane I looked at the plugs. I did not like what I saw. They just did not look good to me. So I shelled out the dough and replaced them. Before I changed the plugs. I tried everything, three pulls with choke on, four pulls with choke on, two pulls with choke on. No matter what I did it took around 20 pulls on the prop to get her running. Once running she ran fine. If you shut her off she would not restart at an idle, you had to give her some throttle.

After changing the plugs, pull four time with mag off and choke out. Leave throttle at Idle, push in choke make mag hot and she starts on the first pull of the prop. She will sit there and idle. Before I would count around twenty pulls after shutting off the choke before she would start. I would also have to leave it just above an idle until she got a little warm then she would idle. None of this now. I set her to idle to start her. When hand propping this is what I want.

Tony

#### TFF

##### Well-Known Member
Before shut down lean the engine till it just barely runs at idle. There is no load so it's not going to hurt anything. Get it lean so the plugs will be cleaned ready for next time. Run for a min or two. You should not blast fine wire plugs but mass electrode type can be blasted clean.

#### Pops

##### Well-Known Member
Log Member
Seeing how I only fly single ignition as many experimental do, not all but a lot. More then you see in the GA world anyway. This is not about swapping top for bottom but just rotating them.

I came around to all this not because I like spending money and just wanted a new set of plugs. This engine was getting hard to start. When I purchased this airplane the owner told me he had no idea why it was getting so hard to start. He double checked everything and everything was right on, timing and such.

When looking over the airplane I looked at the plugs. I did not like what I saw. They just did not look good to me. So I shelled out the dough and replaced them. Before I changed the plugs. I tried everything, three pulls with choke on, four pulls with choke on, two pulls with choke on. No matter what I did it took around 20 pulls on the prop to get her running. Once running she ran fine. If you shut her off she would not restart at an idle, you had to give her some throttle.

After changing the plugs, pull four time with mag off and choke out. Leave throttle at Idle, push in choke make mag hot and she starts on the first pull of the prop. She will sit there and idle. Before I would count around twenty pulls after shutting off the choke before she would start. I would also have to leave it just above an idle until she got a little warm then she would idle. None of this now. I set her to idle to start her. When hand propping this is what I want.

Tony
Tony -- My 1835 starts the same way. I can start it the first blade 95% of the time hot or cold. If it changes, something is not right.

Boy-- Is this fun.

#### N8053H

##### Well-Known Member
Before shut down lean the engine till it just barely runs at idle. There is no load so it's not going to hurt anything. Get it lean so the plugs will be cleaned ready for next time. Run for a min or two. You should not blast fine wire plugs but mass electrode type can be blasted clean.
When shutting down my engines I always do this. Shut the fuel valve off, let it sit and idle until she dies. I then close the mixture and shut the mag off. No way the engine will start unless the fuel is turned on. Doing this solves a couple problems. It leans the cylinders and cleans the plugs as you mention it also makes so I can never take off with my fuel off. My engine will never start if I do not turn my fuel on. If for some reason a P-lead should fail also no way the engine can start if someone pulls or moves the prop. The cylinders are dead. I have unloaded the gun. Everyone should do this when shutting down. IMHO. You don't leave a loaded gun laying around. Don't leave a loaded cylinder hanging around either.

How I do things.

Tony

#### Dan Thomas

##### Well-Known Member
I came around to all this not because I like spending money and just wanted a new set of plugs. This engine was getting hard to start. When I purchased this airplane the owner told me he had no idea why it was getting so hard to start. He double checked everything and everything was right on, timing and such.

When looking over the airplane I looked at the plugs. I did not like what I saw. They just did not look good to me. So I shelled out the dough and replaced them. Before I changed the plugs. I tried everything, three pulls with choke on, four pulls with choke on, two pulls with choke on. No matter what I did it took around 20 pulls on the prop to get her running. Once running she ran fine. If you shut her off she would not restart at an idle, you had to give her some throttle.
Almost all plugs have an internal resistor. The "R" in REL indicates that these do, too. Champion has long had troubles with their resistors. They were, until a couple of years ago, a little thing about an eight of an inch in diameter and maybe 3/8" long, held against the electrode by a spring and little threaded plug. If you look down the outside end of the plug you might see that little screw. It has a slot in it. New production plugs don't have that plug; the resistor is molded right in during manufacture.

Anyway, that spring-loaded resistor would lose contact somehow, maybe through heat and oxidation and vibration, and the resistance would shoot way up from the normal range of 1000 to 5000 ohms up to 50K or way more. The plug got hard to fire under compression. We have sparkplug pressure testers for finding that, but the ordinary Joe can use an ohmmeter to measure the resistance between the firing end of the center electrode and that little plug inside the bore.

Auburn used to make the best plugs in the industry. They had the molded-in resistor, and they would fire until the electrodes got too thin, which would take 800 hours of really hard use. Their warranty was 400 hours. Champions never get that far with the old resistor; I've had them fail at 50 hours and one brand-new right out of the box. The crazy thing is that Champion bought Auburn maybe ten or 12 years ago and shut them down but didn't incorporate their design until just recently. Tempest and Unison/AC use the molded-in resistor as well.

The resistor isn't for RF suppression. It's there to cut off the spark sooner and limit electrode erosion. If its resistance gets too high it cuts the spark off altogether, which makes for hard starting and rough running and big mag drops and can cause arcing inside the magneto. Doesn't do the mag any good at all.

#### N8053H

##### Well-Known Member
Dan Thomas thanks for the info. I would take it there is no other plug on the market to fill the gap or take the place of the REL 37B or others would be using said plug and not the Champion. I never did like Champion plugs. Their non aviation plugs have a weaker spark then the competition. When in school we had a cylinder head that was clear that fit on a small engine. We would use different plug brands and see in the real world what these plugs would do under pressure. Champion always came out at the bottom of the chart when we were done. NGK I believe was at the top and equal to a few others. The Champions would fire a nice spark when not under pressure. But under pressure they would have a weaker spark then any of the others. They were the worst of them all.

Then I get into aviation and I have to use Champion Plugs. I was hoping their aviation plugs were better but was not holding my breath on that. Then in doing my research I came across some of what you said. They talked about the resistors in these plugs. Then they spoke about how this was fixed. I wondered about that. Like I said, never was a fan of Champion plugs.

I also did notice the new REL 37B plugs did not have this screw when looking down into them. It looked more like a rivet or something. I thought oh great this looks cheesy. But now you say no this is better then the screw in deal. Good to know they have corrected this, I hope. For what they cost anyway. Again I am glad I only needed 4. I paid 52.50 each not counting shipping. That hurt for spark plugs.

Tony

#### N8053H

##### Well-Known Member
Well I was wrong. Those new plugs do have the same screw in thing down the middle to hold the resistor in place. I just check. Not sure why I thought I saw different. It may have been another set of plugs I was looking at from a friends airplane and confused the two. But I was indeed wrong.

Tony

#### Dan Thomas

##### Well-Known Member
Well I was wrong. Those new plugs do have the same screw in thing down the middle to hold the resistor in place. I just check. Not sure why I thought I saw different. It may have been another set of plugs I was looking at from a friends airplane and confused the two. But I was indeed wrong.

Tony
Old stock can take some time to clear out, and I don't suppose Champion really wants to throw the old ones away and replace them with the new design.

DON'T remove that little screw plug. Taking it and the resistor out, then putting it back together, somehow disturbs things in there and it might not fire properly after that. A guy might get away with it on a new plug, but an old one could have arcing damage and debris that ends up between the contact points in there. I've tried it.

#### N8053H

##### Well-Known Member
Dan Thomas again thanks for the info. I am one of those that believe if you do not know what you are doing leave it alone. Because of this, I never gave it a thought of removing this screw. On an old unusable plug I may do this to look inside, but not one that would go back into service. Just how I do things.

Tony

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