Fitting the wrong index spark plugs

[Bugone]

Today, I've ordered a set of the wrong index spark plugs, to fit in my Insight.

Why? Well for a start, they were going cheap - but my decision was based on more than just that.

I understand the logic of indexing. I'm assuming that plugs A,B,C,D are all identical bar the electrode being 90 degrees different to the last, orientated to the thread. From reading here, it appears that virtually all insights are mostly B, or failing that, an A.

To me, that indicates that Hondas manufacturing was pretty precise, but the exact back of the engine for most engines is somewhere between plug A and B, nearer to B. The exact back could be up to 22 degrees off of where the plug electrode actually ends up before a different index plug would of been used.

Now in my logic, the idea of indexing is less about having then electrode at the back, and more about not having the electrode at the front where it would get in the way of the fuel air reaching the spark. So as long as the electrode is within the 180 degree back area of the chamber, the engine is going to run virtually identically.

My engine has Bs marked on it, and I've ordered a set of As. I should add, if the correct index plugs were easily available, I would have ordered them. These were much cheaper though. They are genuine honda ones.

Hopefully they will arrive tomorrow, and I can fit them at the weekend and report back. Fingers crossed my logic holds up.

[Cobb]

You could always mark the electrode location on the insulator top with a sharpie, then use washers to space the plug so it seats where it needs to be.

Yeah, Ive been tempted to try diff plugs in the newer insight, but its 2 per a cylinder.

[Bugone]

Originally Posted by Cobb

You could always mark the electrode location on the insulator top with a sharpie, then use washers to space the plug so it seats where it needs to be.

Yep, I plan on doing this, as opposed to using a torque wrench. I was going to mark my spark plug tool, line the plug up in it, and not remove it from the plug as I do it up (it's not a ratchet).

[Eli]

Indexing the plugs in the Insight has nothing to do with the front and back of the engine.

You want the open end of the electrode to face the non-VTEC intake valve; the one that opens all the time.

This is one of those things where you aren't going to be able to tell a difference without sophisticated equipment. If the "A" plugs cause a 1HP loss in power, you're going to be hard pressed to find it with all of the other variables present out on the road.

So in my opinion, it's best to leave well enough alone in this case.

[theaveng]

Originally Posted by Bugone

the exact back of the engine for most engines is somewhere between plug A and B, nearer to B. The exact back could be up to 22 degrees off of where the plug electrode actually ends up

I've no clue what you mean by "back". Back of what?

I suspect as the plugs are removed and replaced, the thread gradually lengthens and the plug is not precisely aligned. Or you might have a mechanic who doesn't care & just twists them on without regards how "deep" they go into the hole.

[Bugone]

Originally Posted by theaveng

I've no clue what you mean by "back". Back of what?

The engine?

This head schematic shows what I mean. The plug electrode is facing the back of the engine in this diagram.



In reality, even if you have the correctly indexed plug, it could be nearly 45 degrees out. (Not 22 - got my angles muddled).

[Eli]

That diagram does not show and is not meant to show the plugs as they are in the cylinder head when properly indexed. It's just an exploded view.

This is what properly indexed plugs look like from the combustion chamber side:



Again, the open end of the electrode needs to face the non-VTEC intake valve.

[samwichse]

That's a nasty looking head... one of yours?

[Eli]

Nah, it's a picture I found online a long time ago. Indeed, it looks like the center cylinder was burning a lot of oil.

[Bugone]

Thanks Eli, that's really useful. So the plug gap faces west, north west in the car? Rear facing north.