Just pulled the spark plugs in my new to me 440 and they are not the same size as the ones I got to replace them. What are the chances?

[tonyp25]

I noticed that the plugs were not the same on both sides so I decided to change them. I believe my 440 is out of a 1975 motorhome.

On one side were autolite 3926 and on the other side NGK BKR6E11. They are 5/8 and I cannot find either of them listed for 440/383 engines.

I bought plugs off of Rockauto Champion 14 and NGK 3332. They are 13/16.

Am I losing my mind? Can I put my 13/16 size plugs in? Did the people before me just put whatever plugs they could find into the car?


First picture is of the two different plugs I took out and the second is of the new plugs I have. I have 8 of each I just wasn’t sure if I wanted to go with champion or NGK. Last picture is them side by side.

 

[pnora]

Pull the valve covers and get the casting numbers to identify what heads you have.

 

[tonyp25]

Pull the valve covers and get the casting numbers to identify what heads you have.

Would pictures of the engine block help? I take it there Are there a lot of heads that fit a 440 block.

 

[RemCharger]

Looks like it's the tapered seat motor home heads

 

[pnora]

Would pictures of the engine block help? I take it there Are there a lot of heads that fit a 440 block.

View attachment 1897524

View attachment 1897525

View attachment 1897526

No. Numbers would be proof positive. You could try to get a picture of the heads plug holes.

 

[tonyp25]

Looks like it's the tapered seat motor home heads

Ahhh if that’s the case I bet they take different plugs than a non motorhome 440. I also guess the only way I’m going to feel good driving this is taking the valve covers off. The frustrating thing is the only thing the guy did before I bought it was put new valve covers and seals on it. I was just excited to have a 440 that wasn’t leaking from the seals.

 

[tonyp25]

No. Numbers would be proof positive. You could try to get a picture of the heads plug holes.

No. Numbers would be proof positive. You could try to get a picture of the heads plug holes.

Got it. Sounds like that’ll be my weekend project. I still don’t understand why the NGK and Autolite plugs I took out do not cross reference each other.

 

[tonyp25]

Also for what it worth here’s what the plugs looked like. One plug looks completely gunked up (cylinder 6). Not sure what that means.

 

[khryslerkid]

Motor home taypered seat plugs don't always have a seal (washer) on them. The motor home heads have a notch right next to the plug hole so you can't use the larger plug.

Plugs with a ring or crush gasket. See the recess...

Taypered plug. Note the bump.

 

[khryslerkid]

You might have two different heads

 

[tonyp25]

Motor home taypered seat plugs don't always have a seal (washer) on them. The motor home heads have a notch right next to the plug hole so you can't use the larger plug.

Plugs with a ring or crush gasket. See the recess...
View attachment 1897551


Taypered plug. Note the bump.
View attachment 1897552

My eye sight is not what it used to be and trying to get my fingers in there is a bit hard. Having hard time from the two clear photos I could get as to whether it’s tapered or not.

If it is a motorhome head how do I find the right spark plugs. It doesn’t look like Rockauto really has the option for any of the motor homes built in the 70s or any of the other sites I buy from.

 

[tonyp25]

You might have two different heads

Haha is that even possible? Why would someone do that and wouldn’t the engine run rough?

 

[khryslerkid]

Haha is that even possible? Why would someone do that and wouldn’t the engine run rough?

Are your pictures of both heads?

They're taypered plug heads in your pics.

See the little bulge below the hole.

 

[tonyp25]

Are your pictures of both heads?

They're taypered plug heads in your pics.

See the little bulge below the hole.
View attachment 1897597

Got it thanks. They are of both sides. I guess I’m going to have pull the valve covers because I just can’t figure it out. I have a bore scope but can fit it in the breather holes to get the numbers. From looking the autolites up they didn’t fit a single mopar engine. The NGKs fit a few later model 1990 dodges.

The less dirty side is the driver side (more silver) and the side I coated in penetrating oil is the passenger side (more brown).

 

[dodgeboy440]

Haha is that even possible? Why would someone do that and wouldn’t the engine run rough?

Without Actually Verifying The Heads Have
Matching Numbers and Are The Same ….
YES you could have different heads on your motor !! The engine would run . Albeit not
Correctly due to the mismatch in head Volume which would vary the compression!!
YES it would run But It Is A Dishonest Repair In My Opinion . Someone In The Engines 50+ Year History Certainly Could Have Effected A Half Assed Repair Because “ They”
We’re Too Cheap To Source A Matching Replacement……

SO what Are The Numbers On Each Head ?

There Awaits You’re Answer My Friend !!

Mopar2ya!

 

[tonyp25]

So with some persistent I was able to get my borescope through the breather opening. Just not sure where to look for the numbers…any pointers where to look?

Without Actually Verifying The Heads Have
Matching Numbers and Are The Same ….
YES you could have different heads on your motor !! The engine would run . Albeit not
Correctly due to the mismatch in head Volume which would vary the compression!!
YES it would run But It Is A Dishonest Repair In My Opinion . Someone In The Engines 50+ Year History Certainly Could Have Effected A Half Assed Repair Because “ They”
We’re Too Cheap To Source A Matching Replacement……

SO what Are The Numbers On Each Head ?

There Awaits You’re Answer My Friend !!

Mopar2ya!

So with some persistent I was able to get my borescope through the breather opening. Just not sure where to look for the numbers…any pointers where to look?

 

[khryslerkid]

So with some persistent I was able to get my borescope through the breather opening. Just not sure where to look for the numbers…any pointers where to look?

 

[Vaanth]

I noticed that the plugs were not the same on both sides so I decided to change them. I believe my 440 is out of a 1975 motorhome.

On one side were autolite 3926 and on the other side NGK BKR6E11. They are 5/8 and I cannot find either of them listed for 440/383 engines.

I bought plugs off of Rockauto Champion 14 and NGK 3332. They are 13/16.

Am I losing my mind? Can I put my 13/16 size plugs in? Did the people before me just put whatever plugs they could find into the car?


First picture is of the two different plugs I took out and the second is of the new plugs I have. I have 8 of each I just wasn’t sure if I wanted to go with champion or NGK. Last picture is them side by side.

View attachment 1897498

View attachment 1897499

View attachment 1897500

Got it thanks. They are of both sides. I guess I’m going to have pull the valve covers because I just can’t figure it out. I have a bore scope but can fit it in the breather holes to get the numbers. From looking the autolites up they didn’t fit a single mopar engine. The NGKs fit a few later model 1990 dodges.

The less dirty side is the driver side (more silver) and the side I coated in penetrating oil is the passenger side (more brown).

View attachment 1897610

View attachment 1897611

Judging from your pictures of the spark plug holes, you have motor home heads. due to the tapered hole for tapered seat spark plugs, and the presence of the small hump which prevents the installation of the standard 3/8"reach gasketed plug. The 3/4" reach plugs that were in there was someone's misdirected attempt to get a plug to install past the little hump.

Regular passenger car big block wedge engines (350, 361, 383, 400, 413, 426 wedge, and 440) all used 14mm, 3/8" reach, retracted (gasketed), 13/16" hex spark plugs.

Mid 1970s and late 1970s 440-3 industrial/truck engines used a 14mm, .460" reach, tapered seat 5/8" hex spark plugs, originally equipped with OBL9Y (Chrysler # 4091938), or substitute RBL9Y, or RV9YC. These were used for additional cooling. The 1973 heads, which covered later years for a time are casting 3751213. Later heads are a modified 4006452 casting. The heads were the similar raw 4006452 casting as other 440 and 400 heads, but were machined differently for the smaller plugs.

361 and 413 heavy truck and industrial, and some marine, engines used a 14mm, 3/4" reach, retracted (gasketed), 13/16" hex spark plug without a projected tip (example, Champion N6). The plugs have a slight angle mount. These heads have the water inlets on the front for the large high mounted water pump and completely different exhaust ports than conventional big block wedge engines. Casting number is 2899943.

For your heads in this application look for the following plugs:

- Champion BL8Y or BL9Y or RBL9Y, which are no longer available new, and replaced by Champion RV9YC.
- Autolite: 23, or for racing: AR23, AR12
- NGK: 2623, or for racing: 5034, 4449

RV12YC is the same heat range as the RJ12YC used with regular big block heads, and is likely the best for your street car application.

 

[R/T Boy 67]

No need for casting numbers, your heads have tapered seats, so just order one of the plugs listed above.

 

[tonyp25]

Judging from your pictures of the spark plug holes, you have motor home heads. due to the tapered hole for tapered seat spark plugs, and the presence of the small hump which prevents the installation of the standard 3/8"reach gasketed plug. The 3/4" reach plugs that were in there was someone's misdirected attempt to get a plug to install past the little hump.

Regular passenger car big block wedge engines (350, 361, 383, 400, 413, 426 wedge, and 440) all used 14mm, 3/8" reach, retracted (gasketed), 13/16" hex spark plugs.

Mid 1970s and late 1970s 440-3 industrial/truck engines used a 14mm, .460" reach, tapered seat 5/8" hex spark plugs, originally equipped with OBL9Y (Chrysler # 4091938), or substitute RBL9Y, or RV9YC. These were used for additional cooling. The 1973 heads, which covered later years for a time are casting 3751213. Later heads are a modified 4006452 casting. The heads were the similar raw 4006452 casting as other 440 and 400 heads, but were machined differently for the smaller plugs.

361 and 413 heavy truck and industrial, and some marine, engines used a 14mm, 3/4" reach, retracted (gasketed), 13/16" hex spark plug without a projected tip (example, Champion N6). The plugs have a slight angle mount. These heads have the water inlets on the front for the large high mounted water pump and completely different exhaust ports than conventional big block wedge engines. Casting number is 2899943.

For your heads in this application look for the following plugs:

- Champion BL8Y or BL9Y or RBL9Y, which are no longer available new, and replaced by Champion RV9YC.
- Autolite: 23, or for racing: AR23, AR12
- NGK: 2623, or for racing: 5034, 4449

RV12YC is the same heat range as the RJ12YC (used with regular big block heads) in heat range, and is likely the best for your street car application.

Thanks so much for help and explanation! If I do go with the RV12YC do you recommend gapping them at .035?

Looks like they come pre-gapped at .04:
CHAMPION 406 Spark Plug | Shop Now at RockAuto