Decided to do a tune up on the Cambridge. Since I have no idea how old the original plugs were I replaced them. Autolite 306 plugs were chosen.

The old plugs were AC Delco, on the left. Compared to the new plug on the right. It's a good idea to compare the old to the new both ways. Make sure the new is physically the same, if it is different find out why. Then compare the old to the new to see if there are any issues to note, such as damage, carbon fouling, etc.

Here are the tools I used to remove the old plugs, prep and install the new plugs. You see the plug socket, there are two common sizes in this case we are using the larger of the two, 13/16". Next you see two types of plug gapping tools, I prefer the wire type. The needle nose pliers were to center the ground electrode over the center electrode, several of the new plugs had them shifted to one side. Probably turd polishing but it doesn't hurt. The ratchet, extension and socket are obvious. Up top we see anti seize and a toothbrush to put it on the plug threads.

Everything has a specification. The service manual calls for a gap of .035" for resistor plugs, .028" for non-resistor plugs. Plug maker calls for 1/4 to 1/2 turn past finger tight when installing the plugs. Old plugs were not that tight, they ranged from finger tight to slightly more than finger tight. The old plug gaps were at .030", new plugs were at .032" out of the box. Slightly smaller is better than too large but lets shoot for the specified gaps. All of the new plugs had the ground electrode centering checked and adjusted, gaps set to .035" then the threads were coated with anti seize and installed, I got about 3/8 of a turn past finger tight.

Last thing we do is look at all the old plugs. I labeled them as I took them out. You want all your plugs to look very similar. If one, or more deviate from the rest there is likely an issue. Look at a plug reading chart and see what the issue might be and investigate. All of mine look good other than maybe being a touch rich based on the carbon on the outer shell. Next step is fuel system adjustments, to be continued...