Spark Plug Issue

[Chief Master Sergeant]

Bought a set of Autolite spark plugs from Autozone and the computer said the 45s were the correct plug; however, when I went to install them they were too big for the plug holes. I had a single Autolite #63 in my tool box for some reason, so I tried it and it fit. Everything on-line tells me this plug won't work. I'm assuming someone put a different set of heads on this thing in the past. Anyone else have this issue? Recommendations?

1967 289 motor

 

[Explorer]

Heads at least have been changed. Ford went from 18mm to 14mm plugs in the 70's.

 

[Chief Master Sergeant]

So, I'm assuming I'll need the stamping on the heads to know what they came off of, in order to find the right plugs?

 

[rustbucket]

Not really. Any 14mm for a SB Ford should work. Gap is more of a function of ignition than anything. If you have some type of upgraded ignition, you can try gapping an extra .010 or more and see how it runs. If you have stock ignition, stick to close to standard. Compression can also be a factor, but I don't think it will matter much with a relatively mild engine.

 

[Explorer]

Looked it up and they changed in 1975, and probably be 302 heads. There is a date code stamped into heads under the valve cover if you wish to go that far to look. What did you take out? Match them up.

 

[Chief Master Sergeant]

This was in the 67 when I bought it. I have been working the wiring and hope to be able to try to start it soon. I wanted to pull the valve covers anyway. Just to ensure there's not a rats nest in there. Found dirt dauber nests everywhere, so better to be safe than sorry.

 

[jw0747]

What did you take out? Match them up.

best advice on here. look at tips of those you removed and if good burn pattern match exactly what you removed.

 

[broncnaz]

I'd just get plugs for a 76 bronco and go from there. check the color after you've run it to make sure they are not to hot or cold.