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Farmall & IHC Tractors Discussion Forum
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H Magneto Impulse.

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richard

12-27-2003 08:23:37




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I am a bit puzzled with the impulse on my 1944 H mag.When the contacts begin to open,the mag has to turn another 10 or 15 deg before the impulse holds the rotor before giving it a flick,so when the impulse works, the heel on the contacts is already on 't.d.c.' of the cam,surely this means that the spark has already occured before the impulse does it's job. Thanks,Richard.




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Diesel Don

12-27-2003 12:16:39




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 Re: H Magneto Impulse. in reply to richard, 12-27-2003 08:23:37  
There is a possiblity that the impulse pawls and/or the pins they catch on are worn and throwing the impulse timing off. The point cam rides directly on the rotor shaft so it can't change. To inspect the impulse coupling, you will need to pull off the nut that holds the cover on, and carefully pull the impulse coupling off of the shaft. Check the corners of the pawls for wear and check the pin. If the pin has a divit worn in it, you can drive it out with a punch and turn it around to an unworn area and drive it back in. Feel free to e-mail me directly with your questions. I recently rebuilt an H4 mag and got to know them fairly well.

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richard

12-27-2003 13:01:34




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 Re: Re: H Magneto Impulse. in reply to Diesel Don, 12-27-2003 12:16:39  
Thanks for your reply but your e-mail is not shown,there are a few questions I would like to ask as this mag has no life about it at all-the impulse coupling it's self is working fine,but the cam was not on the shaft in the corrct place,I have put it where I think it should be(see my reply to Bob below) but it still wont spark, may be you could e-mail me direct so I can get back to you,many thanks Richard.

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Bob

12-27-2003 10:39:43




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 Re: H Magneto Impulse. in reply to richard, 12-27-2003 08:23:37  
If the point gap is correct, the mainshaft with point cam will rotate 'til the cam is just ready to lift the points, and then the impulse will catch and hold the shaft for close to 30 degrees of engine crankshaft rotation. The impulse will "trip", and the points open instantly, so the spark will occur at about TDC. The mag mainshaft will then stop just prior to the points opening on the other of the two cam lobes. The rotor is driven by a 2 - 1 gearset, with timing marks one the teeth for proper assembly.

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richard

12-27-2003 12:51:16




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 Re: Re: H Magneto Impulse. in reply to Bob, 12-27-2003 10:39:43  
Thanks for the info Bob, the cam was out of time with the impulse,I found that it is possible to carefully turn the cam with a 7/16 spanner,I have now set it so when the impulse pawl hits and stops rotation of the rotor,the contacts are just about to break,- stll no spark though! I timed the gear set with the 'R' on the rotor arm gear (right hand rotation of the main rotor shaft looking at the drive dog end?)with the tooth on the small pinion that has the bevel on it,is this correct?

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Bob

12-27-2003 13:10:37




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 Re: Re: Re: H Magneto Impulse. in reply to richard, 12-27-2003 12:51:16  
If I recall correctly, the mainshaft and cam are one piece, and the impulse coupling hub is keyed to the mainshaft. If you are able to turn the mainshaft/cam in relation to the impulse hub, you must have a sheared or missing woodruff key.



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richard

12-27-2003 13:26:56




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 Re: Re: Re: Re: H Magneto Impulse. in reply to Bob, 12-27-2003 13:10:37  
Thanks again Bob,the cam is seperate to the main rotor and can be turned (very tight)the mag was supposed to have been 'done up' before my wife brought it for me for Christmas-she was told the contacts just want cleaning(heard it before!)I can only think it was put together wrong,but it beats me why they would need to remove it, any way its a straight tractor and came with the original log book listing all the owners since it was first registerd for use on January 17th 1945,it also has loads of 'Ministry of fuel and power-petroleum depatment' stamps all over the book from war time rationing,it makes interesting reading.

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