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1939 Allis WC Head Issue
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Buffaloglenn View Drop Down
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Joined: 26 Mar 2023
Location: Buffalo TX
Points: 4 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Buffaloglenn Quote  Post ReplyReply Direct Link To This Post Topic: 1939 Allis WC Head Issue
    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.
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DrAllis View Drop Down
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Joined: 12 Sep 2009
Points: 22013 		Post Options Post Options   Thanks (1) Thanks(1)   Quote DrAllis Quote  Post ReplyReply Direct Link To This Post 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.
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Points: 4 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Buffaloglenn Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jul 2023 at 3:59pm
Originally posted by DrAllis 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.  
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Points: 22013 		Post Options Post Options   Thanks (1) Thanks(1)   Quote DrAllis Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jul 2023 at 5:22pm
If it has equal compression on all cylinders, I think your vacuum thing ain't an issue.
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Joined: 11 Sep 2009
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Points: 2573 		Post Options Post Options   Thanks (1) Thanks(1)   Quote AaronSEIA Quote  Post ReplyReply Direct Link To This Post 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
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Joined: 26 Mar 2023
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Points: 4 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Buffaloglenn Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jul 2023 at 11:08am
Originally posted by AaronSEIA 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.  
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WF owner View Drop Down
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Points: 5035 		Post Options Post Options   Thanks (0) Thanks(0)   Quote WF owner Quote  Post ReplyReply Direct Link To This Post 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.
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