D-17 spark plugs

The 295 is the crossover match from the Champion J8 which Allis used for heavy duty use. Allis used the Champion J11 for medium/light duty which crosses to the Autolite 306.

Edited by Jeff Z. NY - 30 Mar 2010 at 9:02am

I believe that the heads that used the 3/8" reach plugs only had 3/8 of an inch of threads in the head and the ones that used the 3/4" reach had 3/4 of an inch of threads in the head. Just pull a plug and measure the threads in the head and that will tell you what reach plug to use.  Rick

I would not rely on the plugs one takes out of your  D-17 s or 45s because I have seen on several occations that they have the wrong length plug put in . When I got my D-17 it had the short plugs in it with deep threads holes. Had to ream out the inner threads, I also got a 45 that had the long thread plugs in it but had it's factory 45head on it. They were very hard to get out of head.

Dave,
To try to answer your question, and try to be accurate, when it came to the D17 in particular, I think AC went by the serial number of the Tractor to determine what it had for the correct application for spark plugs. Autolite lists 5 different numbers of plugs in the Autolite book for the D17 in particular for its different fuel & combustion chamber applications. As the guys mentioned with reach, spark plug number 64 is used when a 3/4" reach cylinder head is used. The 295's are used with a 3/8" reach cylinder head. A D17 using low grade fuel is supposed to use a 306 which is also a 3/8" reach plug. If the D17 runs on LPG, the 303 number plug is used which also is a 3/8" reach plug. There's also an optional plug for the D17, which also is for the D19, a 2540 plug number. Sooo, that tractor took a lot of different spark plugs to say the least! As far as the reach is concerned, the 64 Autolite which is a 3/4" reach plug has 14mm threads as does the 3/8" reach 295, so the reach is not determined by the size of the spark plug hole. The reach is determined by the length of the threaded shank and how shallow or deep the plug decends to the combustion chamber of the cylinder head its designed for. This obviously is super important to know being it determines the performance of how the engine will run. HTH  BTW, I carry ALL the different numbers in stock that pertain to AC engines and their applications.
Steve@B&B

Mitch,
Thanks for the history lesson on the D17 cylinder head. I've never seen one off an engine, just going outta memory of what my book references, and the needs of my customer's. I understand different piston dome configurations can make a big difference also. Just like in racing engines. I just pulled an Autolite book off the shelf cause' I was curious of how many plugs for the AC gas engines have a 3/8" reach. Most, according to the book it looks. There's only a small handful that are 3/4". I've been an Autolite dealer for over 30 years, and its been a while since I looked up plug profiles, & construction. I always try to be aware of the heat ranges and the applications they can effect mostly.....
Steve@B&B

I have a D17 Series 4 gas, serial number 83495.   What plug should I have in it?  When I went to NAPA and they looked it up, they gave me an Autolite 404.   Is this the wrong plug?  Since I changed plugs it has been running like crap, but I haven't isolated exactly what is causing it.  Might be points and condensor as I haven't replaced them, or could be junk in the carb, as I have been having problems with that also.  I put an inline fuel filter in the fuel line to help eliminate that, but I am probably going to drain and flush the tank also to try and get most of it out. 

Well, the plugs I took out were 3/4 reach plugs so I figured these were right, so will they work?  

Thank you very much Gentlemen, this has been an education for me.  Now if I could only retain. Dave.