The 1947 - Present Chevrolet & GMC Truck Message Board Network

The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)

- Engine & Drivetrain (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=24)

- - Spark plug (https://67-72chevytrucks.com/vboard/showthread.php?t=733563)

Having spark plug issues. Need some help. 66 truck with 250. Original plug is AC 46N. Suggested replacement is AC R44XLS. Which has a 13/16 head. The threads and reach seem fine but when I get the plug into the head there is no room left for a socket to tighten it up. I am wondering if the head has been changed somewhere along the way or am I missing something. What plugs are you running in your 250? The plugs that were in the truck when I bought it are an NGK iridium plug UR5GP that is so short it really doesn't seem to be the correct plug.

Figured out the head was replaced at some point to a newer style with tapered seat spark plug. Ended up using a R44LTS6. Truck is running the best now since I've owned it.