Technical DODGE 318 POLY 18MM SPARK PLUGS

I have a 1964 DODGE W300 POWER WAGON it has the 318 poly engine. It has the 18mm spark plug thread. When i bought spark plugs for it they gave me 14mm long reach, the plugs i pulled out were 18mm Just trying to figure out if this is stock or what. There is 2 bolts on each valve cover toward the ends holding them on. Does anyone know anything about these 18mm plugs.

 

Someone sold you spark plugs for the more modern LA or Magnum 318. DO NOT use them. They may fit and work without the piston hitting them, but after a some use the longer threads on the plugs that hang into the combustion chambers will get coated by the combustion process, and you won't be able to get them out of the heads without damage to something.

1966 was the last year a Poly 318 was installed into a Chrysler produced in the USA. All of the other Mopar small blocks used the long reach plugs, the early Poly motors were the only small block Mopar motors that used the short reach plugs.

I just checked with Champion sparkplugs on line plug listings.
Your 63 Dodge Power Wagon (looked up as a W200) Poly 318 (5.2) motor plugs are Champion part #14.
The part number for a 1970 Dodge Cornet with a 383 (6.3) is champion plug part #14.

The Dodge big block uses the same plug as your poly 318. Someone sold you the wrong plugs (probably what they had in stock), for the newer 318(5.2).

 

Gene, pretty sure he can’t use them if he tried. I believe he’s speaking of thread diameter?

 

look up 1964 W300 on rockauto, they list both sizes of plugs, depending if you have the 318-1 or 318-3 engine. The engine type is cast on the block, but generally the "industrial" engine used the larger plugs, and has the heads with the extra cooling p***age in front.

https://www.rockauto.com/en/catalog...2l+318cid+v8,1330120,ignition,spark+plug,7212

so lesson learned, you need to know more about what you're buying than the guy at the parts store...so you can direct him to what you really need.

 

Alot of people would have taken an old plug with them to the part's store to match or cross reference to another brand. Not alot of room for error, there.

 

Autolite and NGK make 18mm copper plugs. I used them in my Ford Y-block.

 

the long tail 331-2V hemi used short reach plugs.

 

Yep! Had to get new plugs when I switched to 1954 Chrysler Hemi heads and intake on my '52 331 engine.

Dave