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Todd44 
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Location: MN
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 Topic: D17 Spark Plugs
Posted: 13 Jun 2012 at 2:02pm |
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I am changing the spark plugs on a D17 series IV with a serial no. 76428. The plugs that I am taking out are champions with a 3/8" thread length. When I look in the shop manual that my grandpa has for his D17 series IV it calls for 3/4" thread length either: Champion N-8, Auto Lite AG-5, or AC 45XL. If anyone could help out and know what plugs work out that would be great!
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mlpankey
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Posted: 13 Jun 2012 at 2:27pm |
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Ngk bp5es
Edited by mlpankey - 13 Jun 2012 at 8:59pm
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Gerald J.
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Posted: 13 Jun 2012 at 2:36pm |
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Check the thread depth in the head. You don't want plugs longer than the threads.
Gerald J.
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mlpankey
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Posted: 13 Jun 2012 at 2:46pm |
 Gerald J. wrote:
Check the thread depth in the head. You don't want plugs longer than the threads.
Gerald J.
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why is that.
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Todd44
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Posted: 13 Jun 2012 at 2:47pm |
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The thread length in the head is 3/4", but the plugs that the original owner used were 3/8". Now the threads that were exposed are filled with carbon. So I don't know if I should run a spark plug thread chaser through it and put the longer plugs in or just replace the plugs with the same that I pulled.
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mlpankey
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Posted: 13 Jun 2012 at 2:54pm |
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s use the longest reach plug you can without mashing the electrode if looking for performance
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Burgie
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Posted: 13 Jun 2012 at 5:35pm |
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AC 45 XL
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"Burgie"
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Bill Long
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Posted: 13 Jun 2012 at 8:29pm |
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When we sold them we were very pleased with AC plugs. The AC45, AC47, and AC48. However, that was some 50 years ago. I hear that the Auto Lights are now the plug. Contact Steve NJ. He has the correct numbers.
Good Luck!
Bill Long
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Steve in NJ
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Posted: 13 Jun 2012 at 8:43pm |
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If you're using a 3/8 reach spark plug, the 295 Autolite's are 3/8 reach. If you're supposed to be using the 3/4 reach plug, then the Autolite 64 is the number you want to use. Unless it's an LPG version where you would use Autolite 2594. HTH
Steve@B&B
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Gerald J.
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Posted: 13 Jun 2012 at 10:02pm |
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You don't want threads exposed in the cylinder for a couple reasons. First the threads can get to glowing and so make shutting down by turning off the ignition not work. Then the exposed threads can get covered in carbon and make it unreasonably hard to extract the plugs (like plugs breaking instead of coming out and penetrating oil won't help).
You can make any old 3/4" reach plug into a carbon cleaning tap by grinding a notch into the leading threads with the corner of a grinding wheel, or with a cutoff wheel. You'd like one face, the one that would cut while turning clockwise, to be nearly perpendicular to the thread so it cuts more than mashes. Or you can find taps for spark plug threads that are mostly metric and unique to spark plugs since the early 20th century.
Short reach plugs put the spark in the spark plug hole, not exposed to the whole mixture and should hurt performance and fuel economy.
Gerald J.
Edited by Gerald J. - 13 Jun 2012 at 10:03pm
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mlpankey
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Posted: 14 Jun 2012 at 7:22am |
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The plugs exposed threads will never get hotter than the ground strap if ignition timming is set properly. Carbon could be a problem if plugs dont get changed out in a couple of years .
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Butch(OH)
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Posted: 14 Jun 2012 at 8:41am |
mlpankey wrote:
Carbon could be a problem . |
No, carbon WILL be a problem with removal, there is no "if" about it.
Life is differant in the work field than on the playing track. Sometimes knowledge crosses over, sometimes it doesn't. Here it doesn't.
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mlpankey
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Posted: 14 Jun 2012 at 9:21am |
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I have never had a problem with removing plugs due to carbon. I change plugs once a year and remove them and read them often in the field throughout the year. At the track they get read every time its at a track which lately means the ones in the field get looked at more. pet pev i guess
Edited by mlpankey - 14 Jun 2012 at 9:21am
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Todd44
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Posted: 14 Jun 2012 at 11:23am |
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Most of my resoucres that I have contacted have recommended using an Autolite 405 or 64. Does anyone know, which one would be better than the other? Thank you for all the great advice!
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Butch(OH)
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Posted: 14 Jun 2012 at 2:32pm |
I use the 405s in ours and they work fine
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Ky.Allis
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Posted: 14 Jun 2012 at 6:14pm |
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I have used autolite 64's in my D-17 ser.3 for years with no problems at all. Personally,I think autolite is the best plug out there. I use them in every gas engine I own.
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