Farm Equipment - D17 Series 4 spark plug confusion

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D17 Series 4 spark plug confusion

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=208253
Printed Date: 21 Sep 2025 at 12:51am
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: D17 Series 4 spark plug confusion

Posted By: Rusty Allis
Subject: D17 Series 4 spark plug confusion
Date Posted: 20 Sep 2025 at 9:54pm

Well...

Long story short is I had to pull a plug and noticed that it had Champions (yuck) in it but the plug was a short reach RJ12C plug.

I did find this thread:

https://www.allischalmers.com/forum/d17-spark-plugs_topic52040.html" rel="nofollow - D17 Spark Plugs - AllisChalmers Forum

But...it seemed to kind of trail off without any definitive answer.

The threads are LOT longer, so after some digging it looks like I need the long reach plugs.

1) am I correct thinking it really should have the long reach plugs in it and

2) will NGK BP5ES be ok?

and..."while I'm there" can anyone suggest a good set of wires? Delco? Bosch?

Thanks!

Replies:

Posted By: KJCHRIS
Date Posted: 20 Sep 2025 at 11:04pm

we find both short and long reach plugs in them. In theory early D17 will be short 3/8" thread (Autolite 295) and later will be long reach 3/4" thread (Autolite 405). The split is tractor at s/n 75000 / 75001. BUT as D17's are 60+ yrs old you can find some have been pieced back together.

Always check the heads thread depth to verify which length plug it should have.

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AC 200, CAH, AC185D bareback, AC 180D bareback, D17 III, WF. D17 Blackbar grill, NF. D15 SFW. Case 1175 CAH, Bobcat 543B,