I am new to A 1918 model T and finding A lot I do not understand. The engine runs, starts hard cold, easy when warm it seems to me that it should have mower power in high gear. with that said I purchased A new set of plugs & wires. upon taking out the old plugs I found that they were only in 2 turns which seems to me that they should go in farther than that. Shouldn't they all but bottom out on the threads? if so I will need to run a tap in to clean out the remaining threads in the head or should I just use a wire brush.
Here's a 2012 thread about Model T spark plugs, perhaps this will be of some help:
The plugs are 1/2" pipe thread unless you have an aftermarket head. The threads are tapered. They get bigger the further they screw in until they are tight. They do not bottom out.