Farm Equipment - WD spark plug type

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WD spark plug type

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=159484
Printed Date: 10 Sep 2025 at 7:03pm
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Topic: WD spark plug type

Posted By: Fog1950
Subject: WD spark plug type
Date Posted: 30 Mar 2019 at 5:05pm

Hi guys, just did a valve job on my '51 WD. It has Autolite 295's in it now. Curious about the spark plug length into the cylinder. Looks like the recommended plug is shorter than it should be. Has anybody in the group used a long shank plug in their WD? How has it worked?

Replies:

Posted By: acd17toy
Date Posted: 30 Mar 2019 at 7:08pm

The short spark plug is the correct one for your tractor.

Posted By: DrAllis
Date Posted: 30 Mar 2019 at 7:41pm

Late WD's had the taller WD-45/D17 style cylinder head on them from the factory and they would use 3/8" spark plugs. BUT, if the tractor ever had a NEW cylinder head installed on it after about 1960, it just might require the longer 3/4" long spark plugs. You've gotta know what your looking at.

Posted By: DougS
Date Posted: 30 Mar 2019 at 7:45pm

The edge of the spark plug thread should be flush with the inside top of the chamber in the cylinder head.

Posted By: Fog1950
Date Posted: 30 Mar 2019 at 8:26pm

Thanks for all the comments. I appreciate your knowledge.