Spark Plugs

[170C]

Annual times a coming! I am going to do an owner assisted annual this year. First one in 5+ yrs so I am trying to remember all the things I've heard, done before or read here. When removing the spark plugs from our engines is it important after cleaning and regapping them to put each one back in the same location (same cylinder & same top or bottom) from which they came? If so what is the theory behind it?

[Bruce Fenstermacher]

No it's not important if you get one in a different hole.

In fact best practice for maximum plug life is to rotate them. Has to do with the direction of electrical spark. Half the plugs are fired with the electrons jumping from the center electrode to the outside the other half in the other direction. I can't remember which direction it is but one direction wears the center electrode faster.

I don't have the specific sequence to rotate the plugs or where you can find it but I'm sure someone will.

[AR Dave]

Bottom (B) & Top (T)
B1 to T6 / B2 to T5 - - T6 to B1 / T5 to B2
B3 to T4 / B4 to T3 - - T4 to B3 / T3 to B4
B5 to T2 / B6 to T1 - - T2 to B5 / T1 to B6

[mrpibb]

When pulling plugs, it is important where they came from, especially if you find some problems later on during the inspection (story to follow later) for example metal in the screen/ filter, low compression etc. as far as putting them back after cleaning and gapping, it doesn't really matter.

[N2865C]

From Sacramento Sky Ranch:

The spark plug's firing polarity causes uneven electrode wear. The magneto sends a positive voltage down one lead and a negative voltage down the next lead and so on . Each ignition lead always fires the same voltage (on horizontal-opposed engines.

You can see the whole article here: http://www.sacskyranch.com/faqsparkplug.htm

Their FAQ's page has lots of good info on other things as well: http://www.sacskyranch.com/faq.htm

[GAHorn]

It may help to know that as a magneto fires each plug in sequence/firing order,.... that firing polarity reverses each time the next plug is fired by THAT magneto. Therefore it's a good idea for maximum plug life to rotate the plugs to the next (alternately reversed polarity) position. Some folks go a step further and also rotate them top to bottom, etc. In the latter case, any given plug would be rotated to the next firing positon of the other magneto. (I said it this way because some folks have not kept the original convention of the left mag firing the lower plugs and the right mag firing the upper plugs. If the original configuration is applicable, then it's a simple matter to just move each plug to the next firing position, but swapping upper for lower, lower for upper, etc.)

[AR Dave]

I called my mechanic to verify my rotation guess and get an explanation on why to rotate the plugs top / bottom. He walked over to the Champion Rotation Chart, hanging on the wall above the spark plug conditioning bench, and verified as I read my post. It is the correct rotation!

Bottom (B) & Top (T)
B1 to T6 / B2 to T5 - - T6 to B1 / T5 to B2
B3 to T4 / B4 to T3 - - T4 to B3 / T3 to B4
B5 to T2 / B6 to T1 - - T2 to B5 / T1 to B6

The spark plug electrodes are constantly wearing from the center to outer or from the outer to the center. This means the centers are wearing on some and the outers are wearing on others. So obviously rotating them to even out the wear will extend the life.

Lead, carbon, & other combustion deposits, cause spark plug fouling, particularly with the lower plugs. When these accumulated deposits are suddenly raised above their melting point, molten metal forms. By rotating lower plugs to the top, it gives these plugs a chance to clean up, burning off mettle deposits and etc.

I might be off a little but that’s pretty close. It sure made sense the way he explained it to me anyway. Seems to tie-in with our reasoning for leaning discussions.

[GAHorn]

Yes, it's the switching polarity that causes either the center electrode or base electrode to wear more than the other. (Negatively charged electrons sitting on an electrode are attracted to and flow to the positively charged electrode. When they make the leap, they take a little bit of metal with them in the form of erosion.)

Switching between top/bottom theoretically shouldn't make any difference since we supposedly clean the plugs while they're removed, but it's a common practice with the idea to spread the "difficult-duty" of the bottom plugs around. (Some folks install fine-wire plugs in the bottom positions because they are less susceptible to oil-fouling than massive electrode types. It's a common "quick fix" for an oil burner also, and the fine-wires usually last much longer than massive electrode plugs do.)

While on this subject, I got home last night to find my new Unison plugs sitting in a FEDEX box on the kitchen island. When I'd ordered them, they wanted a credit card, and a shipping address. I wanted to pay cash instead, and wanted to save shipping, so they agreed to email me when they came in and I could come by and pay for them when I picked them up. I'd deliberately not wanted them shipped because I drive right by the place to/from work each week.
I'd rec'd an email this week from Air Power that they were now instock and I could pick them up, so I emailed a reply I'd stop by this week. But here they are sitting on the kitchen island having been shipped to me FEDEX.
Then, at breakfast Jamie mentions they'd arrived yesterday, C.O.D. !
(The neighbor down the road works for FEDEX and saw them at work ready to be sent out on the truck, so she picked them up and brought them to Jamie, who (having no idea I'd even ordered them) wrote a check for them.)
Shipping them to me COD added $30 shipping! I only bought them to have on hand for the future. Kinda hurts the reason for buying them on SALE. (Can't very well refuse the shipment now since the payment is already made by the wife, who thought she was taking care of matters for me. Guess I'd better start letting her in on my activities a little more.)

[Bruce Fenstermacher]

Y....... Guess I'd better start letting her in on my activities a little more.)

George you may want to reconsider this statement and just take your lumps with the extra shipping this time

[170C]

George, I probably won't be the first to say this, but I know what a certain blonde would tell me under the same circumstances--------"IT'S CALLED COMMUNICATION"

[cessna170bdriver]

George, I probably won't be the first to say this, but I know what a certain blonde would tell me under the same circumstances--------"IT'S CALLED COMMUNICATION"

The problem with us guys though, is that it's not always obvious to us (until it is too late) just what it is that needs to be communicated.

Miles

[Bruce Fenstermacher]

I myself have been working on an telepathy technic for the last 27 years. I think it's working fine. My wife on the other hand does not.

[170C]

Understood! Bet most of us guys could write a book on that subject.