A Tale of Two Plugs

[Roadrunner777]

A newer member had some confusion about the appearance of the spark plugs, particularly how some are full threaded and some are not. They are functionally the same, as I hope my drawing will show. It is an unusual design, and it took me a while to see how it worked. Hopefully this will clarify things for others.

 

[natenkiki2004]

I had seen this before and came across some information where someone had said that Ford changed things to the full-thread plugs because one of their engines (maybe the SOHC?) was blowing plugs out of the holes.

The real question would be; are the holes on the OHV Explorers fully threaded or partially to match the plugs?

 

[TMW]

if you go to an auto parts store and get plugs for a 91- 92 x they list 765's short thread...for a 93-94 x they are 605's long thread. but they both fit in a 1994 x mine had 765's but calls for 605's and the heat range is different d15 for 765 and d16 for 605....mine has 605's now like it should have.

 

[natenkiki2004]

TMW, I see mixed information about the heat range for 605 vs 765. Some sites say that the last number of Autolite's part numbers is the heat range. Summit Racing shows the two plugs have the same heat range number; 5. However looking at other websites, I do see D15 and D16 mentioned. I still haven't found any official word from Autolite directly though.

 

[Roadrunner777]

I had seen this before and came across some information where someone had said that Ford changed things to the full-thread plugs because one of their engines (maybe the SOHC?) was blowing plugs out of the holes.

The real question would be; are the holes on the OHV Explorers fully threaded or partially to match the plugs?

They are partially threaded... I use the plugs with the partial threads. To test this, just unscrew a plug. If it is fully threaded, it will take roughly 10 full turns. Partial will be 5 or 6 turns.

 

[TMW]

TMW, I see mixed information about the heat range for 605 vs 765. Some sites say that the last number of Autolite's part numbers is the heat range. Summit Racing shows the two plugs have the same heat range number; 5. However looking at other websites, I do see D15 and D16 mentioned. I still haven't found any official word from Autolite directly though.

i got it off autolites site

 

[steelynirvana]

if you go to an auto parts store and get plugs for a 91- 92 x they list 765's short thread...for a 93-94 x they are 605's long thread. but they both fit in a 1994 x mine had 765's but calls for 605's and the heat range is different d15 for 765 and d16 for 605....mine has 605's now like it should have.

Good thing I ran across this. I've got a 93 but found out the other day that its a 91 or 92 motor in it

 

[swshawaii]

SOHC spark plug is also 1/4" longer.

http://www.therangerstation.com/tech_library/4_0_Page.shtml