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Discussion Starter #1
OK. I’ll admit it. I am techno-lame.:oops: I have searched for the answer to this conundrum but can not find it so I will humbly accept a link or a brief terse answer. What does the 4th spark plug do?
 

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Dunno !
Ly around in the trunk as a spare ? :lol:

Give us an answer. :wink:
 

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As I understand it, the engine is only 3 cylinders with four different spark plugs that can be used. The spark plugs are marked A, B, C and D and are matched with the corresponding identification mark for each cylinder, as stamped on the cylinder head.

So, any of four different spark plugs can be used for each of the three cylinders.
 

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I have seen this mentioned in other threads, in varying versions including that there are 4 plugs for 3 cylinders (?) and/or different plugs for each cylinder due to some sort of highly refined engineering process that would require different plugs in each cylinder for high efficiency. No, it doesn't make much sense.

Although I have not inspected the plugs, I do not believe this is the case. In fact, the service manual explains the situation. Apparently there are plugs that are matched to the cylinder HEAD not each cylinder. And that the head could be labeled A-D, with the same letter at each plug.
 

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Discussion Starter #6
Thanks folks-

I think I got it now: The car has 3 cyl. The car has three cyl. heads. Each head is designated to accept one of 4 different plugs. Each car has only three plugs…Right?
 

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spark plugs

Hi Dan,

yep, each car has only three plugs.
 

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http://www.insightcentral.net/encyclope ... plugs.html


Yep, just 3 plugs per car, but there are 64 different possible plug configurations. Each car is unique with this. This is the first time any production car has had this done, though the technology has been used in racing for years. Essentially it along with everything else contributes to the most efficient possible combustion and thus maximum fuel mileage.

If you look through the rest of the Insight encyclopedia about the engine you'll see all the other little things they did. Shot peened pistons to reduce friction, light weight everything. Integrated head and exhaust. It's just amazing what went in to the little engine. There's a reason why it has won engine of the year in the 1L class for several years. Of course they've also won engine of the year awards for he S2000 2.0L 9,000 rpm 240HP engine as well, it's just freakin cool.

Now if you want to get really dazed and confused, the Civic IMA has 2 spark plugs per cylinder, so a 4 cylinder engine uses 8 spark plugs. Each one fires within miliseconds of the other creating a perfect sequential combustion which more fully burns the available fuel in the cylinder. Kinda wish we had that, makes you wounder just how much more potential is there given money is not a factory.

Ok I'll stop ranting now.
 

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The Insight's plugs are _indexed_, it takes a specific plug in each hole. The ground tang's shadow must be in the generally correct location. This is unusual for a non racing application. And is a reflection of how much engineering tweaking that went into the Insights design goal of high MPG. Racing applications usually benefit from indexing to within a couple of minutes in relation to a clock's face. The Insight doesn't require this precision.

As Holicow stated they are matched to the cylinder head depending on where the spark plug threads index. Think of it like the hands of an analog clock. The ground tang's shadow must be in the generally correct location when fully tightened.

More than is needed to know about spark plugs:

http://www.centuryperformance.com/spark.asp

There are 4 differently indexed spark plugs. The index mark is a letter A thru D and is found at the top metal "bullet" where the cylinders coil connector makes electrical contact. The corresponding index mark is stamped on the cylinder head and will be visible with the coils removed.

For each cylinder simply match the stamped mark on the head with the spark plugs mark. Incorrectly indexing plugs or installation of a different style of plug will more than likely effect the lean burn mode. Limiting maximum MPG.

Will someone eventually find some other setup that works? More than likely.

Will it exceed the stock setups performance? (MPG) Not likely.

:)
 

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Rick said:
Now if you want to get really dazed and confused, the Civic IMA has 2 spark plugs per cylinder, so a 4 cylinder engine uses 8 spark plugs....Ok I'll stop ranting now.
The piston engines used in airplanes also have two plugs per cylinder, for the same reason. The ignition system uses two very powerful magnetos, one hooked up to the top plugs and the other to the bottom plugs in each cylinder. Same for a top fuel motor putting out 8000 hp at 9000 rpm, or 1000 hp per cylinder. :shock: Sometimes the old technology is still the best.

Please, never stop "ranting".
 

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Dan.................Only one head, not three.

The Insight plugs are also about 1/4 inch longer than the civic plug (don't know about the HCH) on the threaded part.

And last but not least....................(Torque them to the proper torque)
 

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I stand partially corrected, but I would like confirmation that there are 3 different plugs in each cylinder. What I mean is: can someone confirm that the letters for each cylinder are different? I have not looked, myself.

Could 2 of 3, or even 3 of 3 be the same? Why would the plugs be different in each cylinder?
 

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Discussion Starter #13
Thanks again everyone-

One last but not least question: “Torqueing them to the proper torque” and “aligning the tangs” sounds slightly incompatible. I would assume this would necessitate replacing the little copper o-ring whenever the plug is removed?
 

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For Holicow, yes it could be any combinations. See the top of the plug to know which letter it is. The plug is identified (from the Service Manual)

For Dan, that is a very good question and I do not know. I would not expect a big difference in turn count when a plug is set a second time. Maybe a 1/8 turn? No?
 

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My head is stamped "b" for each one, so all three of mine are the same. I just wonder if the person who measured the head was in a hurry :roll: and just stamped them to speed up.
 

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Sorry for being silly before. I just didn't get the point.....
"insightful trekker" brings it all to the point on the previous page !

Holicow said:
Why would the plugs be different in each cylinder?
Because when you cut threads into any material the chances for it to "begin" at the same place are very slim.

So I say, while all my plugs are also marked "B" :roll:
 

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Discussion Starter #17
Hi everyone-

So maybe the difference in the plugs (A,B,C,D) is a 90 degree change in the angle of the direction of the gap in relation to the threads?
No 166- I regret any unintentional implication concerning your intelligence. Maybe you overestimated my sense of humor. The joke is on me because I underestimated yours (I thought you were serious). I keep rediscovering how easy it is to be misinterpreted here. I guess using those smiley faces helps. I’m trying to pay more attention to them. They just seem a little to much like a cross between a bad acid flashback and a “Tellitubies” episode. I’ll get over it. :wink:
 

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dan said:
Hi everyone-

So maybe the difference in the plugs (A,B,C,D) is a 90 degree change in the angle of the direction of the gap in relation to the threads?
......... :wink:
You're absolutely right. THAT is the difference between the 4 spark-plugs.
:)
 

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"The piston engines used in airplanes also have two plugs per cylinder, for the same reason."

That's only half the reason, though you do notice a distinct RPM drop when only one set is operating. The main reason, though, is redundancy: there are actually two completely separate ignition systems, either of which is sufficient to keep the engine running. If one fails, you can still keep going...
 

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james said:
That's only half the reason, though you do notice a distinct RPM drop when only one set is operating. The main reason, though, is redundancy
I used to think that too, until I started doing accident investigations. To be accurate: the reason for the twin magnetos is redundancy, sort of. Some "dual" magnetos are actually in one unit, and many of them are on a common drive that is much more likely to fail than an individual mag. So, not so redundant, but better than just one. Mags rarely fail.

As for the plugs, the FAA test question answer is for more efficient fuel burn. Remember, those are BIG cylinders with relatively low compression. Not to mention the massive electrode REM 40 E's that most Lyc's and Continentals use. As for the RPM drop, be really careful if your renting airplanes that do this. The maximum drop in most applications is 50 rpm. That's the WORST case. If the mechanic has timed the mags properly, there should be only a slight drop, less than 25. If you get a differential of more than 75, don't fly it. There is a timing issue that will bite you some day. The Barons I fly regularly have an rpm drop of about 10( a needle width). That's because they know how to time the mags properly and use the proper equipment, rather than just "by ear", which I see all the time.

If you fly, please be careful, compulsive and constantly aware. I am getting tired of scooping bodies out of crashed GA airplanes, and it's getting worse.

OOOps, I'm sorry. This is the INSIGHT forum. My apologies.
 
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