Spark Plug Query

[Jmclendon]

Originally Posted by kchampagne

Could you take some pics of the heads? Might help diagnose the issue.
Thanks!

#2

Is there an issue? Or do I just live with 2 different styles of plugs?

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[Jmclendon]

Originally Posted by AZKen

You have to analyze this problem before we can rest. Before we will answer. I know you want to hear to just use them. Go ahead if you do not want to know what is wrong.

Let's not worry about what I want to hear LOL I'm happy to keep digging

Originally Posted by AZKen

If the two different plugs have the same 14mm and one fits and the other does not and the one that does not is short, it has to thread in. It makes absolutely no sense.

I completely agree.... it was weird enough that at first I was just assuming that I was having a moment.

Originally Posted by AZKen

Is the reason it won't "fit" is that the threads won't start? or the hex on the plug hits the casting? or your wrench hits or what????? Are you saying it's too short to reach the first thread in the head????

Most of this is by feel, because I can't see anything. But, the best way that I can think of to describe it is that the plug just free spins. Considering that longer plugs I had in were also 14mm, and they went in fine, logic is telling me it's got to be that the shorter ones are just to short.

Originally Posted by AZKen

do the threads in the head look odd? like a helicoil or some repair plug???

The photo that I took is the best look I've actually been able to have.... But, nothing looks glaringly wrong. When I look at the threads on the plugs that I've pulled (the long ones that fit) they don't look damaged or anything like that.

Originally Posted by AZKen

Can you understand that from here it seems impossible if all plugs have the same pitch/size thread? 14mm.

Completely understand. I spent a couple of hours last night going over it again and again, because it just doesn't make sense.

Originally Posted by AZKen

This seems to indicate a different plug, tapered seat?. I got the feeling it is different mechanically not just spark. Guess what? the Delco 10 has 14mm threads also and is a tad longer than 3/8. If by taper they mean "different" thread shape than 305 plugs, then you could have some heads from the larger motors (if they even fit). If you are using a "normal" plug in a head that is built for taper (whatever that means)

Some digging on the NGK site has provided some clarity.....

https://www.ngk.com/product.aspx?zpid=9371

It looks like the tapered seat (which apparently is all about how it makes a seal) can come in the same pitch and thread size as the gasket style plugs. They're not interchangeable.

[AZKen]

I thought you were asleep and was re writing my post when you posted, that's why it's gone. But you have it quoted. I see it's 5:30PM there, sorry.

It is possible that you have a tapered head with non tapered plugs that "seems" to fit. That is what we are both thinking. That's what Turbobill said way back. If that is possible, you don't want that. Others will chime in tomorrow. BigBlockV6 has a post talking about tapered for larger motors. D10 plug.

ALSO: Your spark plug hole picture does not look right at all for 305. Is that a weld fillet holding in an insert or greasy spot painted orange? What the **** is that? It's either what Big V6's look like or it's a fix. That's what FMAP said way back. Show a hole in the other head.

Thanks to K for asking for a picture.

[Jmclendon]

Originally Posted by AZKen

I thought you were asleep and was re writing my post when you posted, that's why it's gone. But you have it quoted. I see it's 5:30PM there, sorry.

It is possible that you have a tapered head with non tapered plugs that "seems" to fit. That is what we are both thinking. That's what Turbobill said way back. If that is possible, you don't want that. Others will chime in tomorrow. BigBlockV6 has a post talking about tapered for larger motors. D10 plug.

ALSO: Your spark plug hole picture does not look right at all for 305. Is that a weld fillet holding in an insert or greasy spot painted orange? What the **** is that? It's either what Big V6's look like or it's a fix. That's what FMAP said way back. Show a hole in the other head.

Thanks to K for asking for a picture.

enlarged picture of the #2 (one of the ones that won't take the short plug [all 3 look the same]


Enlarged picture of #1 (one of the 3 that will take the short plug [all 3 look the same]

I can see now that the difference is that the even cylinders are inset. So the short er plug won't ever work because the threads won't reach.


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[James]

It look like sometime in the truck past a head was change out.You might want to make sure the threads in the heads is the same length as the spark plug reach. If the long reach plug is place in a hole design for a head with a short reach the expose threads could cause a couple of problems. It could have a build up of carbon making it difficult to remove the next time and/or could create a hot spot in the combustion chamber and pre-ignite the fuel charge (cause spark knock and loss of power).

My truck heads required the long reach but only the tip half of the plug is threaded into the head. They use to make plugs this way but decided to do away with them to cut their inventory (see picture). I also have two spare set of heads. One is made like the one in my truck the other is machine for a short reach plug.

[Jmclendon]

I can't tell for certain from the picture. But, it looks like the older style plug doesn't have a metal gasket on it, is that correct?

The reason why I'm asking is I'm trying to work out whether or not the plug I need has a tapered or a gasket seat. Is there some way that I can tell by looking at the plug hole?

[James]

Your pictures show the head seat area very dirty, however it look like both of them is taper. Can you clean it up a little better and see if they match one of the pictures?

Looking at my pictures (of my spare heads) the long reach has a squared off seat. The short reach has a taper seat.

[James]

Originally Posted by Jmclendon

I can't tell for certain from the picture. But, it looks like the older style plug doesn't have a metal gasket on it, is that correct?

The reason why I'm asking is I'm trying to work out whether or not the plug I need has a tapered or a gasket seat. Is there some way that I can tell by looking at the plug hole?

Yes that plug picture is a taper seat plug. The pencil is pointing at the taper.

[Jmclendon]

It is a bit atrocious how dirty they are. I hit them with some air while the old spark plugs were in. But, it clearly didn't do the trick.

What have you used to get yours so clean? I'm super paranoid about letting anything fall through into the chamber.

[James]

Originally Posted by Jmclendon

It is a bit atrocious how dirty they are. I hit them with some air while the old spark plugs were in. But, it clearly didn't do the trick.

What have you used to get yours so clean? I'm super paranoid about letting anything fall through into the chamber.

I use an awl, the one you normally would see with a 90° bend on one tip and the other end is straight with the plug install about half way in, and scrap around the plug. Then I use a air nozzle with a long small snout to blow out all loose debris. Then I removed the spark plug and insert a rag large enough to plug the hole and finish cleaning and blowing it off.