Plugs for a 318 Poly

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Professor Fate

Professor Fate

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Does anybody have a quick and easy way to tell if a '66 318 poly uses 3/8" or 3/4" reach plugs? Both are used. Don't say "take the old ones out and look at them"- after this many years, who knows if the right ones are in it now. Short of pulling a plug and trying to get in there and measure the depth of the threads in the head, is there a quick identifier as to which plugs a particular head takes?
Thanks guys.
 
Factory Service manual and owners manual tells you plug numbers. They never tell you the reach, you can look that up under the number.
 
413 said:
Factory Service manual and owners manual tells you plug numbers. They never tell you the reach, you can look that up under the number.
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That's the problem- don't have a '66 truck manual, '66 pass car manual says J14Y. Online parts lookup says J14Y or N14Y- the difference being if the engine was U.S. or Canada built (which were used in some but not all U.S. built vehicles). Thus my question.
I was hoping for an easy telltale, but I guess I'll just pull a plug when I get there and try to measure the reach in the head. I'll just throw some Autolite 86s (3/8) in the box and hope I get lucky when I go over there later- nobody around here stocks the 66s (3/4) and I would have to wait a day or two for them anyway.
 
They are the 3/8" short reach. NGK BP5S. Leave the Champions in the trash can.....
 
All the poly 318's I've seen used the short reach plugs....same ones as most of the big blocks.
 
They turned out to be the 3/8 reach, as most have said. It just had me worried as I was researching plug numbers that there could be two variations. My luck is usually having the wrong ones- but it's all good this time.
 
Looks like you figured it out. Fwiw, I had a 66 D100 with a poly and auto. Used the J series Champion short reach big block plugs.
 
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