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Allis Chalmers Discussion Forum

AC B magneto impulse question?

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Robert in Mdt

09-11-2007 18:22:51

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About a month ago my B wouldn.t start, just fire but not run with starter or pulling. Pulled the mag and have a broken impulse spring. I, ve order a new spring from Standard Magneto but haven.t recieved it yet. My question is how do I install the new spring. How many turns on the spring. I tryed looking on the other post about the FMJ mag but it will not come up. Thanks , Robert in Md.

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Robert in Md

09-12-2007 19:34:58

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 Re: AC B magneto impulse question? in reply to Robert in Mdt, 09-11-2007 18:22:51  
Thanks guys for the responses. The broken spring must have been installed correctly because it has lasted 59 years before it broke.

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Steve in N.J.

09-11-2007 20:52:27

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 Re: AC B magneto impulse question? in reply to Robert in Mdt, 09-11-2007 18:22:51  
There is a correct way and a wrong way to install the impulse spring. Assuming it's a "J" model mag which was popular on the B/C model tractors, the eyelet of the spring faces to the right so it winds up correctly. Also, there are two slots in the impulse cam pawl. One deep slot, the other is shallow. The tail of the spring is installed in the deep slot. When winding up the spring, new springs only need about one turn past the pawl locks. Any tighter will bind the spring and break it. Probably what happened to your original. Be careful loading the spring into the impulse pawl. If it gets away from you, it'll smart! Another thing to watch. Make sure after the tail of the spring is in the deep slot, that the pawl tower comes up flush with the top of the outer cup. Any questions, give me a call, be happy to help you out....HTH (973) 632-5596

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09-11-2007 19:34:58

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 Re: AC B magneto impulse question? in reply to Robert in Mdt, 09-11-2007 18:22:51  
Send me an e-mail and I will send you a manual on that mag which may help you with your problem.

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stu (ON)

09-11-2007 19:32:12

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 Re: AC B magneto impulse question? in reply to Robert in Mdt, 09-11-2007 18:22:51  
Robert, I hope that someone can come up with a mechanic's answer for you. On one occasion that I had a spring out, I believe that I reassembled it by feel. You need enough tension that when the coupler releases, the rotor spins fast enough to generate a nice hot, blue spark. This amount of tension probably also give the necessary spark retardation to prevent kickback when hand cranking the tractor. Any more tension than this didn't make sense to me, and may even weaken the spring. Just my thoughts, stu.

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