01-07-2021, 03:24 PM
Sparking plugs are available with different lengths of thread. Without being able to measure the holes in your head I suggest that you may need 3/4 in instead of 1/2 inch. I hope this is your problem. Excuse my quoting inches but that is how they are normally defined from the early days. Metric conversion gives approximately 19 mm and 13 mm to the nearest mm.