Farm Equipment - 1939 Allis WC Head Issue

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1939 Allis WC Head Issue

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=196017
Printed Date: 07 Oct 2025 at 12:32pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

Topic: 1939 Allis WC Head Issue

Posted By: Buffaloglenn
Subject: 1939 Allis WC Head Issue
Date Posted: 05 Jul 2023 at 3:10pm

I've been rebuilding my Allis WC and just got the head back from the machine shop and installed on the block. All valves appear to be opening and closing by looking at the rocker movement from top down. Strange thing is that it is only pulling vacuum on the intake port that feeds cylinders 1 and 2. The port that feeds cylinders 3 and 4 is not pulling any vacuum.

Any thoughts would be appreciated. I'm not ready to take the head back off, although it seems like I will have to.

Thanks.

Replies:

Posted By: DrAllis
Date Posted: 05 Jul 2023 at 3:37pm

All valve lash settings should be at .015" COLD. Actually use a compression tester and see what each cylinder has.

Posted By: Buffaloglenn
Date Posted: 05 Jul 2023 at 3:59pm

DrAllis wrote:

All valve lash settings should be at .015" COLD. Actually use a compression tester and see what each cylinder has.

Thanks for the advice. Compression is between 90 and 100 for the four, assuming my cheap gauge is reasonably accurate. Will check the valve lash settings.

Posted By: DrAllis
Date Posted: 05 Jul 2023 at 5:22pm

If it has equal compression on all cylinders, I think your vacuum thing ain't an issue.

Posted By: AaronSEIA
Date Posted: 06 Jul 2023 at 5:45am

No way it can build compression if it's not pulling a vacuum. What symptom are you trying to fix?

AaronSEIA

Posted By: Buffaloglenn
Date Posted: 06 Jul 2023 at 11:08am

AaronSEIA wrote:

No way it can build compression if it's not pulling a vacuum. What symptom are you trying to fix?

AaronSEIA

Thanks - I figured it out this morning, as I still had one spark plug in cylinder #1, so it built compression and pulled vacuum from the front port, but not the back where I had no spark plugs. Oops.

The issue is the tractor won't fire. I've got a freshly rebuilt magneto with spark, a clean carburetor and have it timed but it won't do anything. Engine was yard art for 20+ years, so I tore it down and had the head redone at a shop. All seems well with new valves and a freshly machined head. Liners and bearings were okay so I cleaned up the pistons and put on new rings.

Posted By: WF owner
Date Posted: 06 Jul 2023 at 12:24pm

Are you sure you have it timed to spark at the top of the compression stroke? Don't forget that the magneto turns half the RPM of the crankshaft. It's very easy to have the mag 180 degrees off.