magneto timing
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=8739
Printed Date: 19 Jan 2025 at 2:51pm
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Topic: magneto timing
Posted By: Dan (MN)
Subject: magneto timing
Date Posted: 27 Feb 2010 at 7:35pm
| I am reassenbling a 39 WC engine, I know that the timing marks on the crank and cam shafts are lined up, I put the governor on so the drive lugs for the mag are horizontal, I put the mag on so the rotor pointed to the timing mark on the big mag cover. I tried to start the tractor and I get nothing. The carb is off a running WC so I know i am getting fuel. Where on the mag do I look to find my issue, if I impulse the mag by hand I can see a spark at the points, but I get no spark at the plugs. Any help would be great. Dan |
Replies:
Posted By: Ken in Texas
Date Posted: 27 Feb 2010 at 8:34pm
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There should be timing marks on the governor gear too. They must be lined up with the cam to time the mag. The drive lugs will then be where they are supposed to be. Not necessary to be horizontal.
If you snap the grounded mag by hand with a plug wire and grounded spark plug it should fire the plug on 1 of the 4 snaps
On the tractor bring the #1 piston up on compression. Note where the rotor is ready to snap and fire next. Thats Plug # 1. It goes 1-2-4-3. Varoom
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Posted By: Ken in Texas
Date Posted: 27 Feb 2010 at 8:45pm
| I should have mentioned the governor/mag timing mark lines up with the cam gear mark that is 180 degrees from the cam to crank mark. |
Posted By: TomMN
Date Posted: 27 Feb 2010 at 11:26pm
When cylinder number one is at TDC on compression stroke is when the impulse spark needs to happen on startup. All magnetos that came on the WC fired on the horizontal like all standard Fairbanks-Morse mags. You can easily test your mag if it is off the tractor, turn the impulse coupler by hand and look where it is when it is ready to snap - if it is a regular mag it will be horizontal. The easiest way I have found to know you have the number one cylinder at TDC is by looking at the crankshaft pulley, the set-screw on the pulley points straight down on the WC (it points up on the RC). So with the spark plugs out you can feel with a thumb in the spark plug hole of number one when air is being pushed out as the hand crank is slowly turned, this is the compression stroke. Then just slowly continue turning with the hand crank until the crankshaft pulley set screw points straight down and you are at TDC. This is when the spark from impulse needs to occur so the mag coupling has to be horizontal with the crankshaft in this position.  |
Posted By: TomMN
Date Posted: 27 Feb 2010 at 11:35pm
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Upon reading your post again I see you are asking maybe more about how to verify if your mag is working. Here is a link to how to time the gears of an FMJ magneto, I know it was helpful to me when I was doing my WC. Tom http://dueyschutter.freeservers.com/photo6.html - http://dueyschutter.freeservers.com/photo6.html |