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Tractor Talk Discussion Forum

In Need of Information on Magneto....

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Keith-OR

04-08-2004 22:17:19




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Is there an arc when the points open as there is when the point open with a system using coil? While cranking engine over cover off mag system have no arc when points open. What I know about a mag system you could put in a thimble and it would run out...So could use all the help I can get. thanks




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Keith

04-09-2004 21:16:03




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 Re: In Need of Information on Magneto.... in reply to Keith-OR, 04-08-2004 22:17:19  
I checked to see if I had spark with condenser removed (disconnected), I have spark. Bought a new one, hooked it up,no spark, If I leave the condenser out of the circuit, have good spark for the first 4 or 5 revolutions then spark becomes weak. Just curiuos am using 12 volt battery to run starter, could I be running the mag to fast to produce hot spark.I do not hear the mag making the clicking sound as it turns over at highspeed. Or maybe I need to check the mag and find out why it is out clicking during the highspeed start mode. Am going to get 6 volt battery tomorrow and see if that makes a difference
Thanks for all the good info. I am learning alot so far. Seems to still be some hope for this old mechanic

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RAB

04-10-2004 00:44:25




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 Re: Re: In Need of Information on Magneto.... in reply to Keith, 04-09-2004 21:16:03  
Keith,
If you operate without a condenser, the points will spark and the high temperature will oxidise or burn your contacts - keeping them apart by that film or tiny deposit. Reduced current will quickly/immediately lead to no spark at the output. That is precisely why that component is fitted to the system. I have not had a condenser failure on one of my mags yet.
Instructions with all(?) hand-start tractors impressed the owner NOT to 'swing' the engine over to try to start it, but just to let the impulse coupling do its job as a better spark is obtained that way. If your engine has one, make sure it is working properly.
You do not tell us what mag or engine. There are better makes/models of mag, different types (moving coil or moving magnet). Some are inclined to losing magnetism more than others (and giving less current could be your problem).
BUT, generally, the problem is keeping the breaker points clean and gapped exactly as the instructions. You also need to remember not to use resistor type components in you system (carbon fibre leads, resistor type plug caps)and to keep the plug gaps at, but not much more than, the specification, not to fire into an open circuit, even if you have checked the internal safety gap is operating OK. If the breaker cam is worn, it could possibly be opening the points at a time when the generated current is not at the maximum. Other problems can be encountered by not knowing how to put them back together timed correctly if they are adjustable for both rotations.
I use American Bosch revolving magnet mags mainly and have very few problems with them.
Regards, RAB

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Keith

04-10-2004 08:57:21




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 Re: Re: Re: In Need of Information on Magneto.... in reply to RAB, 04-10-2004 00:44:25  
RAB thanks for the info. The mag is a Fairbanks Morris type J and It is on an Allis Chalmers 126 CI gas Model C 1948. I am doing most of what you suggested, copper wires, original rotor,new plugs "non resistor type" Have cleaned the points,checked to see if they were burnt or pitted, neither one. Got my old points file out of the tool box, has cob webs on it for the lack of use on today modern engines, run it between to points to make sure no pits and good and clean. Been doing mechanic work most of my life, but never really got into the magneto part untill now, never to late to learn though. I am going to pull the magneto today and clean it up and check for the obvious things that could be wrong. AND probably be back in here on the forum picking everyone brains on what can possibly be wrong...lol Thanks again for the education and great info
Keith

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RAB

04-09-2004 12:30:55




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 Re: In Need of Information on Magneto.... in reply to Keith-OR, 04-08-2004 22:17:19  
Will perhaps need cranking quite fast to see any sparking at the points. Theoretically there should be none - the condenser should absorb the energy until the points are too wide to spark.
A lot of magnetos sytems have an impulse coupling to improve the spark energy at hand cranking speeds - ie dead slow. The mag stops turning, while a spring system winds up, then flicks over fast at the appropriate time. Usual problem with a mag is high resistance across the points. No current equals no spark energy. Clean and set the points carefully as per specs - the points opening is timed to be at maximum current production from the mag generating system.
Regards, RAB

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Coloken

04-09-2004 06:48:51




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 Re: In Need of Information on Magneto.... in reply to Keith-OR, 04-08-2004 22:17:19  
Yep, fires when points open. Just like a battery/coil, only generates its own current from the armature, then sends it to the "coil". Some times points get "glazed". Coil can be checked with ohlm meter.



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Nor. Al

04-09-2004 05:23:15




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 Re: In Need of Information on Magneto.... in reply to Keith-OR, 04-08-2004 22:17:19  
Kieth You have either a dead coil or condensor most likely , I hope its the condensor as they are not too expensive and the coil is.The coil is the box on top of mag. where the wire comes out and goes to the center of the cap. Usually the condenser comes out from the side, from behind where the "kill switch wire " or "ground out " fastenens to it. I hope I may have been of help & hope you get it to firing.

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sibby(Aus)

04-09-2004 01:28:27




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 Re: In Need of Information on Magneto.... in reply to Keith-OR, 04-08-2004 22:17:19  
Keith, does it have a condensor fitted in conjunction with points, if so try disconnecting condensor and then turn over and see if any sparks? i am not real sure either. good luck!!!



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