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Minneapolis Moline Tractors Discussion Forum
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JTU magneto question

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Kelvin

08-21-2005 12:33:29




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I am trying to fix a Minneapolis-Moline JTU to run, It has a Waukesha engine.

The magnet on the Original Fairbanks RV4B magneto is dead. I have tried to start it on a Fairbanks FMJ (I'm not sure what it came off of) but all I get is a pop every now and then. The magneto has a good spark.

My manual only shows only how to set the static timing (At top dead center), but not the run timing.

Can I install the RV4B impulse on the FMJ to be sure I am getting the correct spark advance?

If you don't know, can you suggest someone I could check with?

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Glen in TX

08-21-2005 13:06:42




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 Re: JTU magneto question in reply to Kelvin, 08-21-2005 12:33:29  
Kelvin, The FM-J mag you are trying to put on needs to be CW drive facing the drive end and have UA stamped on the impulse drive cup. The striker pin would also be on the lower RH side. The hub assembly with the pawls inside will have 35 degrees stamped on it. That is the type you want for your JTU. Most RV4s had a earlier style impulse but I think it should work ok if the pawls aren't too worn out. The FM J just has a different striker with it being made inside the cup that bolts on to the housing. The FM-K4A4 was the recommended replacement for the FM-RV4A4. A FM J or X with the same rotation and correct impulse will work fine though. Why did the RV4 magnet go dead anyway? Bad bearings? Early RV4s were cobalt magnets but can be recharged unless someone has welded on it or ruined it.

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Kelvin

08-21-2005 17:51:44




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 Re: JTU magneto question in reply to Glen in TX, 08-21-2005 13:06:42  
Thanks for the reply. The magnet in the RV4 is rusty between the laminations and I read in some book about repairing magnetos that is what pretty much finishes them off.



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Glen in TX

08-21-2005 19:14:02




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 Re: JTU magneto question in reply to Kelvin, 08-21-2005 17:51:44  
Sounds like your RV4 had the old cobalt style magnetic rotor with laminations. Later on they replaced those in the RV style mags with a stronger solid Alnico type magnet. If the rest of the mag is good yet don't throw it away as someone might want it for parts. Don't have any of those magnets for a RV4 right now. Also if you didn't have the 35 degree impulse hub I have some of those outright or exhange if your old one is good.

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