Carboned plug holes?
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Freshman User
Joined: Dec 2003
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From: BC Canada
Carboned plug holes?
I'm about to start a plug change on my 1998 F150 4.6 which has only 78,000 km and went to my local Ford dealer to get the latest Motorcraft sparkers. The originals only have about 5 threads on them and these are threaded all the way down. After removing a couple of plugs that came out no problem, the new ones will only screw in about 5 threads and then stop. I tried to go past this but don't want to strip or otherwise screwup the threads. Has anyone else encountered this? I'm thinking that the lower threads are carboned up and need cleaning. Would a tap do this okay without damage?
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Postmaster
Joined: Mar 2004
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From: Michigan
Sounds like you might have gotten the wrong plugs,I would match up the new ones to the originals,they should be same length and same thread length,I have never had to rethread one of these engines,is this happening on all the plug holes?
Logistics Pro
Joined: Jul 2003
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From: Lawton, Oklahoma
Two spark plugs of the same length, regardless whether they are threaded all the way up or only partially threaded will still only go in to the point of fully seated on the body of the plug to bore. Think about it, if the plugs would go in an extra half inch or farther, then the piston would strike the plug causing greivous damage. Those spark plugs could be designed to work on numerous engines with various bore depths but all seat at the same point on the plug.
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Freshman User
Joined: Dec 2003
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From: BC Canada
It was the same for two holes and I quit after that. I asked the dealer to recheck and explained the difference and he said the new ones were correct. Sorry, don't remember the number as I'm at work just now. When comparing the two plugs side by side, the old one has a long lower unthreaded portion from the tip up to the 5 threads then the sealing flange. The new one is same length tip to flange but threaded all the way down. Both are Motorcraft.
Postmaster
Joined: Mar 2004
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From: Michigan
I guess I should have been a little more specific,I did mean from electrode to shoulder length,but anyway,I dont think I would use a tap to rethread the holes,how would you get excess material out of the cylinders?In the 25 years that I have been a service tech I have never had a carbon build up stop a plug from going in,there have been times when it made them a little stiffer to put in,but never stopped one completely.I would like to know the plug numbers on both the old and new plugs before I comment on anything else.
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Freshman User
Joined: Dec 2003
Posts: 26
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From: BC Canada
Okay, I'm an idiot! You guys were correct. Old plugs are AWSF 32PG and new ones are AGSF 32FM. The new ones only go in 5 turns and do indeed seat on the shoulder. I new they were the same length but seeing all those threads made me want to use them. The salt on the wound would be that my "wife" wanted to know what my post was about. You know what's coming don't you? Yes, I showed her both plugs and explained my problem. She said I have no problem as they both shoulder at the same time. I QUIT. She does all the maintenance now!!
Thanks for the replies.
Thanks for the replies.
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