View Full Version : spark plugs
jts359
10-10-2021, 10:08 AM
Hi With the advice of several posters I purchased a set of 3924 autolite plugs , Now I have Ford cast iron heads which i believe to be 1993 vintage , The plugs I took out were motorcraft platinum asf 42 p which have a reach of 3/8 approx and the 3924 have a 5/8 reach ? I got out my bore scope and there are only 8 threads in the head which means the 3924 plug is protruding into the combustion chamber by 5 threads almost 5/16 of an inch ! I'm concerned about hot spots etc. There appears to be no interference with valves or pistons , Bear with me here as this car has been a interesting but fun learning experience , Any thoughts , TIA Ed
Remove those plugs and install the proper reach -- sooner than later.
jts359
10-10-2021, 12:08 PM
I didnt start the car with them installed , Ed
J R Jones
10-10-2021, 05:01 PM
NAZ is right. The plug obstructing the combustion chamber flow is disadvantageous to efficiency and the exposed threads can become caked with carbon. That complicates plug removal and may damage the head threads.
jim
jts359
10-10-2021, 06:55 PM
I realize the issue with the reach of these spark plugs and one reason I made the original posting is there may be people who don't and should made aware of problems that may be caused by them, Ed
J R Jones
10-10-2021, 07:56 PM
Ed,
The Autolite cross reference is 3263, or AP25, or AR25, but I would go with NGK or Denso.
jim