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Mag timing for a Allis Chalmers C

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John99

10-12-2005 16:32:43




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Need help in timing a magneto for an Allis Chalmers C. The motor was rebuilt by a commercial rebuilder. The valve timing appears to be correct but I am having problems timing the mag to 30 degrees BTDC. The best I can get is 10 degrees BTDC. The tractor will not start with the starter motor but will run if pulled to a start. I have attempted to trick the system by trying to set the mag greater than the 30 degrees. This did not work. I believe the valve timing is correct because I can look into number one cylinder and watch the valves close as the piston comes up to TDC. I have followed the book on the mag timing by meshing the gear tooth with the C of the distributor gear, aligned the distributor rotor with the timing boss, rotated the crank to the fire mark on the flywheel 30 degrees BTDC on the compression stroke, and couple the mag to the engine. This is where I have the problem. Using this procedure, the mag does not trip until about 30 degrees after TDC??? By tricking it and coupling the mag at about 60 degrees BTDC, I can get it the timing to10 degrees BTDC. The question isdo I have a problem with the mag or could the mag/governor gear by mis-aligned? Before I pulled the front of the engine apart, I wanted to ask for any other thoughts or advise. Also, if the cam and crank gears are aligned correctly, is it possible to just pull the mag/governor gear and reposition it without removing the cam and valve train? ps. the tractor was greatgrandpa"s and parked for over 20 years before my grandson and myself started our rebuilding project.
Any help is greatly appreciated!

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steve(ill)

10-12-2005 19:36:13




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 Re: Mag timing for a Allis Chalmers C in reply to John99, 10-12-2005 16:32:43  
fire at TDC. the advance will run at 30 BTDC when motor is above 600 RPM.



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CHALMERSBOB

10-12-2005 18:56:55




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 Re: Mag timing for a Allis Chalmers C in reply to John99, 10-12-2005 16:32:43  
IF THE TRACTOR RUNS WHEN PULLED AND SOUNDS GOOD THEN THE TIMING IS REASONABLEY CORRECT. HOWEVER THE IMPLUSE COUPLING ONLY COMES INTO PLAY WHEN CRANKED EITHER BY HAND OR ELECTRIC STARTER. TURN BY HAND AND LISTEN FOR THE SNAP. IF IT DOESN'T SNAP, REMOVE AND TAKE A LOOK AT IT. BOB



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Dick L

10-12-2005 18:04:14




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 Here Are A Few Pictures in reply to John99, 10-12-2005 16:32:43  
The first is just a drawing.

third party image


Next is the actual engine at TDC. Same as the drawing.

third party image

This picture shows the TDC looking straight at you on the flywheel and the number one piston at TDC.

third party image

The last picture shows the magneto drive position which is straight across or horizontal.

third party image

More to follow later. I need to get back to work.
If your gears are timed correctly the drive will be in this position.

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John99

10-13-2005 04:47:18




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 Re: Here Are A Few Pictures in reply to Dick L, 10-12-2005 18:04:14  
Your pictures and descriptions were great. The magneto drive was not in the horizonal position when the crank was a TDC. Can the mag/governor gear be repositioned without removing the cam?
Before I remove the front of the engine, I will try adjusting the mag following your suggestion in your second note. The earliest I can get back out to the farm will be sometime next week. I will keep you posted. Thank you!

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Dick L

10-12-2005 18:27:55




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 The Way I Check From There in reply to Dick L, 10-12-2005 18:04:14  
If the timing gears are all at the correct place. I take all the plugs out, put a plug on number one plug wire, ground the plug base to the block, hand crank very slowly( inching the crank) until I hear the snap and see the spark on number one. Walk around to the other side and make sure that TDC is in the center of the inspection hole.
It should be! If it is not it should be you task to get it there. The advance is mechanical and if started in the described position it will show the FIRE line to a timing light.

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jeffalex2

10-12-2005 17:56:06




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 Re: Mag timing for a Allis Chalmers C in reply to John99, 10-12-2005 16:32:43  
You need to time to the 'center' mark, not the fire mark. The fire mark shows up 30 deg before the center mark, and when mag is timed, you should hear the impulse coupling 'click' right at TDC. Once set up like this, when you time with a timing light, the 'fire' mark is the one you use and center in the site hole. I've found the manuals to be misleading on this point.



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