Indexing Spark Plugs

[qapd]

Why did my mechanic put an index mark on the spark plugs? What purpose does this serve. The mark lines up where the wire attaches to the plug base. What gives here, I have never heard of anything like this before.<br /><br /><br />QAPD <br />Pasadena, Tx

 

[R.Johnson]

Re: Indexing Spark Plugs

This was the correcr procedure on the OMC Ficht engines. I don't know if this needs to be done on the newer engines. It had to do with how the plug indexed with the injector nozzle.

 

[qapd]

Re: Indexing Spark Plugs

Engine is 1998 Johnson 150hp Ocean Pro. It has carbs, no fuel injection.<br /><br />I noticed this weekend while fogging the engine.

 

[Dhadley]

Re: Indexing Spark Plugs

What plugs did he use?

 

[Silvertip]

Re: Indexing Spark Plugs

Spark plug indexing is a process of orienting the plug electrode in a specific way to promote optimal combustion and flame travel. Its been used in performance tuning on cars for years.

 

[walleyehed]

Re: Indexing Spark Plugs

^

 

[qapd]

Re: Indexing Spark Plugs

Dhadley,<br /><br />The plugs are QL78YC. Are these correct?

 

[walleyehed]

Re: Indexing Spark Plugs

I'm not DH of course, but those are the correct plugs.(to the best of my knowledge according to the book)

 

[Dhadley]

Re: Indexing Spark Plugs

Yep, thats fine. I use the alternate QL77JC4 in mine just because they are a tad cooler but youre fine. Just make sure to stick with 87 octane. And dont lug it. 5800-6000 with an average load.

 

[Cricket Too]

Re: Indexing Spark Plugs

I've always done this on my Ficht, but is it worth it to do it on a carbed motor, and if so what is a good way to index on a carbed motor?

 

[walleyehed]

Re: Indexing Spark Plugs

mm, you have an injector shooting fuel straight in the direction of the plug, but in a carbed version, the fuel/air mixture is in a swirling pattern when spark occures and I don't "think" plug position has any advantages, especially on the fixed-gap plugs....

 

[DJ]

Re: Indexing Spark Plugs

Think about it. A surface gap plug would show NO advantage by being indexed, as walleyhed suggests.

 

[DHPMARINE]

Re: Indexing Spark Plugs

DJ correct about surface gaps .Depending on the fuel octane,temp,rpm,etc.,there are advantages as to where 'gappable' plugs point.Problem is ' we' will never do enough testing to know if it helps.That's why we listen to them.Sometimes.<br />Injection is a whole other story.Strange that FICHT engines needed a new plug we never heard of.<br /><br />DHP

 

[seahorse5]

Re: Indexing Spark Plugs

DHP,<br /><br />I'm not sure of what you mean about FICHT having to use a new plug that we never heard of.<br /><br />Can you say the same thing about the Optimax, HPDI, and 4-strokes that all use "new" or special plugs that we haven't heard of before?