#6 plug boot shorts to header

[spdbrake]

Yes it should blow it out. If you have an inspection mirror you may see a carbon spot on the lower side of the header flange at the leak point. Covering the mirror face with soapy water, 409, etc.. and placing it near the suspected leak area will blow the mirror clean when in the hot exhaust path.

[Ozzie Goat]

I believe I can declare victory
I just did a hard and hot 20 miles with no ill effect to the boot

It's the shorty Accel plug. There's a beautiful huge gap to the header now.

NOW, what cruise night is on Tuesday ?

[Ozzie Goat]

Oh, and no spinning the dizzy cap; it was indexed

[Ozzie Goat]

Shorty plug did not work.
Like all the others, it shorted to the header.

Today, I'm again declaring victory.
This time with Summit ceramic plug boots.
Let's see how long this one lasts...

[spdbrake]

(amazingly I was able to log in today...)

Ozzie,

I looked up the NGK-UR45GP you're using. Which is a Conical seat & .460" reach Chevy application plug.
https://www.ngk.com/product.aspx?zpid=10176

What heads are on your 302?

If they're Ford, AFR, Edelbrock you should install a SET of Autolite 3924 (they come pre-gapped at .044") Gasketed base and 3/4" reach.
https://www.summitracing.com/tx/part...SABEgKNv_D_BwE

Just to be safe on the plug reach (depth). A quick check take a 90deg scribe or a piece of wire and bend a short 90 bend at one end. Slide in the spark plug hole in the head until it reaches the inside and can be hooked.
Place your thumb at the opening of the spark plug hole on the scribe. Remove the scribe or wire and measure the distance from the tip of your thumb to 90 deg scribe or wire bend.
If its approx 3/4" the 3924 plugs are safe to use.

I really think you have a pi$$ poor ground at the plug base causing the connection at the plug top and plug wire to overheat at that connection point. Once it melts a hole in the boot it can jump to the nearest grounded metal object.

[Ozzie Goat]

I really appreciate you checking in to assist.
This has been very challenging, and my car - I now think - has always run on seven cylinders.

The heads are described as Ford Racing X #M-6049-X306
I took a look and don't see the plug reach documented. I'll keep looking.

Question: what if I didn't use a boot at all, using just a 90* connector?
What is not there, can not melt and redirect the current.

As of this morning the ceramic boot has not shorted, but since it touches the header I'm adding a heat sleeve to ensure a gap.

Roy

[Ozzie Goat]

I found a reference to these heads using Motorcraft AGSF32C
That plug has .700 reach - so your suggested plugs should be fine.

I'm going to order a set.
Should the engine have it's own ground strap ? or does it ground via motor mount etc ?

[spdbrake]

A good ground from the block or one head to the frame is advisable.

[Gaz64]

Originally Posted by Ozzie Goat

I found a reference to these heads using Motorcraft AGSF32C
That plug has .700 reach - so your suggested plugs should be fine.

I'm going to order a set.
Should the engine have it's own ground strap ? or does it ground via motor mount etc ?

Every engine should have a large lead from the block near the starter to the battery negative terminal, other wise how would the engine crank?

This ground is sufficient for engine ground while the engine is running.

Some engines benefit from grounded cylinder heads, especially with MSD CDI ignition systems.

Gary

[Ozzie Goat]

Thanks Gary.

I checked again, and the only method of ground is that the negative terminal on the battery is bolted to the roll bar in the trunk.
No ground straps at all. No grounding of block or heads.
The MSD grounds to the battery terminal.

I believe SpdBrake is right that my engine ground is dodgy and that could lead to arcing sparks !
Waiting on those new plugs.

[Gaz64]

Originally Posted by Ozzie Goat

Thanks Gary.

I checked again, and the only method of ground is that the negative terminal on the battery is bolted to the roll bar in the trunk.
No ground straps at all. No grounding of block or heads.
The MSD grounds to the battery terminal.

I believe SpdBrake is right that my engine ground is dodgy and that could lead to arcing sparks !
Waiting on those new plugs.

Is this engine solid mounted?

Even if it is, the engine should have at least 00 gauge ground lead directly to the battery negative.

Gary

[Ozzie Goat]

Thanks for all the help.

Gary - the ground strap was under the motor mount.

The new plugs seem much smoother.

I also found #7 was also arching from the boot.
New ceramic boots all around.

Will wait and see.