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  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 " 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
M265                                                                   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
P302, P351, UF-9Y
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 " 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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