Rotating Plugs?

[RyanB]

Sorry in advance for the thread spam today!

I got the oil changed in the Archer this afternoon. Phillips XC + CamGuard and a clean filter, so I’m happy. One thing I actually do like about the shorter change intervals, is having more of a frequent eye on everything under the cowl. Usually during this time, the plugs get cleaned and rotated, but for the sake of time this afternoon, I haven’t yet.

Curious what interval y’all use in regards to rotating your plugs. Each oil change? Wait til annual? And what order do you cycle them? I’ve heard top to bottom, clockwise etc., each person with their own science for doing what they do.

What say you?

 

[Whitney]

Every 100 hours they get cleaned and inspected, and moved ahead 1 cylinder and swapped from top to bottom.
I replace them all annually.

 

[Jim K]

Every 100 hours and/or at annual, whichever comes first. Kind of a shame not to stick a borescope in there while they're out, too.

 

[Bell206]

Curious what interval y’all use in regards to rotating your plugs.

Anytime all the plugs are out or annual. However, some aircraft need it done every 100 hrs or so.

And what order do you cycle them?

For flat engines the easiest method is to follow the Champion or Tempest diagrams as it makes it almost Murphy proof. And keep in mind there is more than one reason to rotate plugs: polarity, lead length, and deposits.

 

[Dan Thomas]

The + and - are the polarity of the plug's firings. The positive electrode erodes faster than the negative. Switching them evens out the wear.

If you use a plug holder like this, you just rotate the holder and reinstall them in the positions they then appear. So the tops all go to the bottom, and #1 goes to #4, and so on. Easy.

 

[Clip4]

Change oil and filter every 35-40, clean gap and rotate every 70, replace plugs 280.

 

[Domenick]

At each 50 hour oil change I run a compression check and pull, IRAN, and rotate plugs.
Don't forget to use new copper gaskets (or annealed gaskets) and anti-seize paste. I prefer the silver paste.

 

[Dan Thomas]

Change oil and filter every 35-40, clean gap and rotate every 70, replace plugs 280.

Replacing at 280 gets expensive. Better to clean, gap, and test with a proper pressure tester, made for exactly that. There is also available a wear gauge to determine when the plug has eroded to limits.

The old Auburn plugs were guaranteed to last 800 hours. I don't think any plug maker has the nerve to do that now. The Auburns were awesome right up until Champion bought them and shut them down. Champs, the old design with the spring-loaded resistor, had a hard time getting to 400 hours.

 

[Magman]

When you have a fleet your perspective may be different. Putting a dab of varying colors of paint to designate hours in service worked well. It was rare that the plugs were reinstalled in the same engine.

Often it’s not the “ cost of maintenance “ but what “ maintenance costs”. By that I’m referring to down time. Swapping out plugs , wheel/tire , brakes and mags can have the aircraft making money sooner . Investing in spares is much more cost effective than buying another aircraft . You DO have to address records and servicing on a rainy day though.

Uh oh. Is Dan trying to relight the Champion vs AC ( Albert Champion ) debate?

 

[Clip4]

Replacing at 280 gets expensive. Better to clean, gap, and test with a proper pressure tester, made for exactly that. There is also available a wear gauge to determine when the plug has eroded to limits.

The old Auburn plugs were guaranteed to last 800 hours. I don't think any plug maker has the nerve to do that now. The Auburns were awesome right up until Champion bought them and shut them down. Champs, the old design with the spring-loaded resistor, had a hard time getting to 400 hours.

At $2-$3 an hour, plugs are not the driver of operating costs and the the headache of a bad plug plug away from home negates any savings by running plugs to their death.

 

[Dan Thomas]

At $2-$3 an hour, plugs are not the driver of operating costs and the the headache of a bad plug plug away from home negates any savings by running plugs to their death.

I never, ever had a plug fail away from home in any of the school's fleet. In tens of thousands of hours. We did the plugs at the 100-hour intervals, and tested them to 135 PSI every time. Plugs that were weakening would show up on the test long before they gave trouble in the airplane. And I would not buy Champions. Auburns up until they were shut down, then ACs and Tempests.

It's easy to say $2 or $3 an hour. That same idea applies to vacuum pumps, alternators, magnetos, filters, tires, brakes, and all the other stuff that is, or should be, periodically inspected or replaced, and soon you're into major costs per hour. If plugs can be tested and reused, you can save a bit of money at no risk. It's far more frequent that neglected magnetos, vacuum pumps and alternators fail and ground the airplane at some inconvenient spot. Even throttle, prop, mixture and carb heat cables have a habit of breaking because they were just run to failure.

Spend the money on the stuff that tends to fail, not on the stuff that doesn't.

 

[Magman]

Many “ bad” plugs are just inflicted with a chunk of lead.

Lots of room to carry a spare.

 

[Jdm]

Lots of room to carry a spare.

I like the way you think. Works fine for those of us who fly around with a tool bag. Unfortunately most pilots aren’t equipped, or capable of troubleshooting and correcting a plug failure. And most shops can easily dig up a serviceable plug if needed.
I received a bunch of shop equipment that came with a recent airplane purchase. One of the items was a brand new ATS spark plug bomb tester box. Nice, but I really need more than just a tester to service plugs. I think I have a pretty good system in place now though. Have the vibrating lead removal tool, various soft blasting media etc. I’ve also started checking resistance on all plugs, a step commonly skipped. I keep a chart of findings to compare with the next round. Champion had some bad years with resistance issues.

 

[Whitney]

Changing plugs annually on my planes has worked well for me, and I'll continue to do so, cheap and easy maintenance item.
I already have new plugs to do me for the next 2 years, spare mags, spare starter, spare alternator, belt, baffle kit, exhaust, tires, wheel bearings, and more. I also change the cables mentioned earlier every 5 years, and keep the ones pulled out as a backup if needed. It really isn't hard to have some spare parts around.
Plan to get the stc soon to pponk it next rebuild, and then start gathering the parts, pistons, rings, jugs, cam, crank, seals, gaskets, con rods, bearings, prop, etc so I have it when the time comes, especially with how hard parts are to get. I'll be ordering extra parts to, and storing them in boxes downstairs with silica packs to keep humidity low.

In my tool kit stored in the back of my plane are 2 new plugs, and 3 plug wires in 3 different lengths.

 

[Wagondriver]

Every 100 hours they get cleaned and inspected, and moved ahead 1 cylinder and swapped from top to bottom.
I replace them all annually.

replace every year? How many hours do you fly per year?

 

[Whitney]

replace every year? How many hours do you fly per year?

Typically 250 ish to 400 ish, but could be more or less.
It doesn't take long, I'll do 11 or 12 hours this week alone, and the same next week. Burger runs, trips to Mexico, sight seeing, visiting friends, and such, so I just feel better replacing them yearly.

 

[jesse]

Typically 250 ish to 400 ish, but could be more or less.
It doesn't take long, I'll do 11 or 12 hours this week alone, and the same next week. Burger runs, trips to Mexico, sight seeing, visiting friends, and such, so I just feel better replacing them yearly.

Happy to take your old ones each year!

 

[MooneyDriver78]

Typically 250 ish to 400 ish, but could be more or less.
It doesn't take long, I'll do 11 or 12 hours this week alone, and the same next week. Burger runs, trips to Mexico, sight seeing, visiting friends, and such, so I just feel better replacing them yearly.

They should last about 1000 hours…I’d save yourself some $ and replace on condition or every other year at most.

 

[Domenick]

I do not doubt it is true, I simply do not understand the mechanism.

How does air pressure affect plug performance?
Does denser air have increased spark resistance?

 

[Dan Thomas]

I do not doubt it is true, I simply do not understand the mechanism.

How does air pressure affect plug performance?
Does denser air have increased spark resistance.

In the plug tester, you start the spark at ambient pressure. You can see a small spark. Start raising the pressure and the spark gets more intense and brighter, as there are now more air molecules to ionize and carry the electron flow. Keep raising the pressure and eventually it will get intermittent or stop altogether, because air is a dielectric (insulator) and there is no longer sufficient voltage to force the electron flow through it.



https://www.championaerospace.com/wp-content/uploads/2015/06/AV6-R-Aug20141.pdf

On checking the internal resistor:

https://tempestplus.com/wp-content/uploads/2019/01/AT5K-Instruction-Sheet.pdf

The "competitive" plug they mention is the old Champion design.

 

[Dan Thomas]

Happy to take your old ones each year!

I used worn-out (eroded) Auburns in my A-65. That little engine doesn't have high compression and didn't get plugs hot enough to cause preignition, and the old Auburns ran better than new plugs of any brand.

Like I said earlier, Auburn guaranteed their plugs for 800 hours. We regularly got over 1000 hours out of them, and it was always erosion that forced their replacement, not a failure to spark.