by Richard A. Day Jr.
All gaps unless otherwise noted are .030"
|Engine Model||Plug Type|
|NK, F, PB, PAL, LH, PH45, PH75, PH120,||7/8" 18 Thd W-18|
|PH135, PH150,||18MM with gasket ½" reach D-14|
|PHC 7/8" Heads||W-10|
|SK, GW, LLH, ZR, PNR, PH134, IH60, M60, YT, HH, BHT,||D-16|
|BHW, BH-25 A little hotter heat range than the D-14||D-16|
|134, 230, 320, 339, 404, 240, 264, 308, 461, V345, V549||D-14|
|M304, M345: Normal service||UJ-6|
|M304, M345: Light service||UJ-8|
|M196, M265, M392, M549, M345B, M392B||UJ-6|
|PW-27 18mm heads||D-21|
|PW-27 14mm heads||UJ-10Y|
|Y304, Y345, Y392||UJ-6|
|PB-V-215 V-8 Model (Gap .035)||L-7|
|MD188, MD301, MD301SM (Diesel)||AG-40|
The above information taken from a Champion Spark Plug data sheet published in 1970. One needs to keep in mind that the very early jump spark engines used ½" NPT plugs like the Ford, Model T "X" plug. Early engines such as the NL, NR, PNR and ZR series used 7/8" plugs such as the W-18. Later production used 18 MM plugs such as the D-14 or D-16 Things like heat range were never even a consideration in these engines. The YT series will be found with heads using either 7/8" or 18mm plugs. So use this data with attention to the actual dimension of the threaded hole in the engine.
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