1940 Allis B starting problem
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=196085
Printed Date: 12 Nov 2025 at 2:00pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: 1940 Allis B starting problem
Posted By: JudgeguyBob
Subject: 1940 Allis B starting problem
Date Posted: 10 Jul 2023 at 6:47am
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Hi, I am in process of rehabilitating a 1940 Allis Chalmers B. Engine has been rebuilt and back on the tractor, but I'm having trouble getting it to run. When there is no compression on the engine, spark plugs are out, the engine spins fast and free as it should normally. When spark plugs are in, and compression builds up and the starter switch is engaged the motor spins very slowly with intermittent hesitations. Battery is new and fully charged, grounding has been checked and rechecked several times, cables and wiring are new and of correct size and connections checked and rechecked. One electrical shop replaced the starter switch, which didn't correct the problem. Another shop replaced the solenoid, again without correcting the problem. Magneto was serviced and tested, and timed with good spark. Is there something I'm missing, perhaps a mechanical issue? And advice would be appreciated. Bob
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Replies:
Posted By: Fred in Pa
Date Posted: 10 Jul 2023 at 7:18am
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DO YOU HAVE A VOLT METER HOOKED ON BATTERY TO CHECK VOLTAGE DROP. ------------- He who dies with the most toys is, nonetheless ,still dead. If all else fails ,Read all that is PRINTED. |
Posted By: steve(ill)
Date Posted: 10 Jul 2023 at 8:44am
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slow cranking is common if you have a 6 volt battery..... but it should start if your getting gas and spark.. Picture hand cranking the engine. Dont have to spin fast.. That being said, you need to verify you have SPARK and TIMED correctly... that is the biggest problem when people install a mag... verify that when you roll the engine by HAND CRANK, that you hear the MAG SNAP when the crank is at TDC ( top dead center) by the timing mark on the left side bell housing inside the 1 inch hole... NOT THE FIRE MARK.... Then verify that when the engine comes up with #1 piston to TDC, that it is actually #1 plug that is getting the FIRE... you can put that plug in the spark plug wire and roll slowly over and see that it sparks...... if you have gas in the carb, it should start. I have 12 v batteries on my B MAG tractors.. They will start when the motor rolls over 1 revolution when cranking. ------------- Like them all, but love the "B"s. |
Posted By: steve(ill)
Date Posted: 10 Jul 2023 at 8:46am
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the FIRE order is 1-2-4-3 ... with 1 at the radiator (front) of the motor. ------------- Like them all, but love the "B"s. |
Posted By: JimD
Date Posted: 10 Jul 2023 at 10:38am
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I know you said correct size on the cables, but give us a bit more info. 6V or 12? What gauge cables? ------------- Owner of http://www.OKtractor.com" rel="nofollow - OKtractor.com PM for an instant response on parts. Open M-F 9-6 Central. We have new and used parts. 877-378-6543 |
Posted By: HoughMade
Date Posted: 10 Jul 2023 at 10:55am
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Starter switch? Solenoid? Too fancy for a B. My 6v mag B starts in 1 or 2 revolutions when I pull the starter rod (as God intended).  Anyhoo, if you have a good voltage supply, I would take apart the starter and clean the commutator and make sure the brushes and bearings are good. I would also clean and dry-lube the bendix. If everything checks out (it has to be functional, not perfect) put it all back together and see how it spins. I'd say something checking and tuning up the plunger...but you've got that high-falutin switch and solenoid. But in the end, if the carb is right and the mac is strong and timed right, it should start if it makes just a few revolutions. Can the spark jump 1/4 inch? It should.
------------- 1951 B |