bn magneto change out to battery ingnition

Farmall B & BN Tractors, 1939-1947

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Dave F.
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bn magneto change out to battery ingnition

Postby Dave F. » Sun Feb 10, 2019 11:59 pm

The magneto on my bn has a bad inpulse spring. (won't snap / trip) I had an extra battery ignition distributor from a 50 cub . I timed the dist. to the engine & it starts right up & seems to run well, Do I need to change the advance weights & springs ? I have a slight miss I think a better or new set off points, condenser, & a better cap & rotor would take care of the miss. Thanks Dave F.

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Re: bn magneto change out to battery ingnition

Postby Jim Becker » Mon Feb 11, 2019 12:26 am

The Cub distributor has less than half the centrifugal advance of the one for a BN. The weights are the same but the springs are different. Also, the max advance is determined by the shaft. So converting it from the Cub to a BN requires a shaft and two springs.

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Re: bn magneto change out to battery ingnition

Postby Rick Spivey » Mon Feb 11, 2019 6:40 am

You'd be better off, imo, to find a decent H4 magneto from a seller or internet. It wouldn't need any corrections. The J4 was Cub specific (C60 engine specific).
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Re: bn magneto change out to battery ingnition

Postby Dave F. » Mon Feb 11, 2019 9:26 am

Jim, would you have the part numbers for the dist. shaft & springs I wonder if they are still available. Thanks Dave F.

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Re: bn magneto change out to battery ingnition

Postby Jim Becker » Mon Feb 11, 2019 11:48 am

The original version for the A/B/H/M was the "A" code distributor, 40 degrees at 1400 rpm. A pair of springs is 358106R91 with shaft 353928R91.
Some later tractors used the "J" code distributor., 30 degrees at 1400 rpm. A pair of springs is 358108R91 with shaft 354901R91.
If your compression ratio has been raised a bunch, you might want to use the later numbers. Messick's shows them all available (although sometimes that isn't completely accurate), springs about $30 a pair, shafts about $130 each.

Rick's suggestion looks pretty good.

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Rick Spivey
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Re: bn magneto change out to battery ingnition

Postby Rick Spivey » Mon Feb 11, 2019 5:54 pm

Rick Spivey wrote:You'd be better off, imo, to find a decent H4 magneto from a seller or internet. It wouldn't need any corrections. The J4 was Cub specific (C60 engine specific).


I misread, and thought you had changed out to a Cub (J4) magneto, not a Cub distributor. Sorry, but to be truthful, the H4 magneto is still a good choice for your BN.
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Re: bn magneto change out to battery ingnition

Postby Dave F. » Mon Feb 11, 2019 7:51 pm

I checked couple of magneto parts suppliers, said the in pulse spring. For the H4 magneto is no longer available. Dave F'

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Re: bn magneto change out to battery ingnition

Postby Eugene » Mon Feb 11, 2019 10:00 pm

You will have to do the research. Some Fairbanks/Morse magnetos interchange with the IH magneto. There was only a slight difference in the lag angle.

I had, sold, an IH magneto from a WC Allis Chalmers that I purchased for parts.
I have an excuse. CRS.

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Re: bn magneto change out to battery ingnition

Postby Jim Becker » Mon Feb 11, 2019 11:11 pm


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Re: bn magneto change out to battery ingnition

Postby Dave F. » Thu Feb 14, 2019 8:30 am

Putz a round with the old mag. The impulse spring was o.k., but the inpulse paws/arms what ever you call them won't engage to trip? must have some wear . Any one know where I could buy this part? Thanks Dave F.

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Re: bn magneto change out to battery ingnition

Postby Rick Spivey » Sun Feb 17, 2019 1:01 am

Dave, the pawls engage 2 pins that are driven into the bottom flange of the magneto. Often, they wear a flat spot on the pins. If so, drive them out, then rotate them slightly, and drive them back in. The pawls will then hit a fresh spot on the pin, and likely the impulse will work again.
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'48 Cub with FH ("Gunny Cub") 38xxx
'57 Lambretta (a slow work in progress)
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Re: bn magneto change out to battery ingnition

Postby Dave F. » Wed Feb 20, 2019 10:38 pm

Rick, Sorry about the late reply. I only found one pin I drove it out and turned in & reseated the pin It didn't make any difference the in pulse still doesn't work. Thanks Dave F.

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Re: bn magneto change out to battery ingnition

Postby Dave F. » Thu Mar 14, 2019 10:45 am

Jim Becker (incase their is more than one Jim.) A while back you said An J code distributor would work on my BN. I found an distributor which has these numbers JE6-914881 IH part #353898R1 would this work thanks Dave F.

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Re: bn magneto change out to battery ingnition

Postby Jim Becker » Thu Mar 14, 2019 4:47 pm

Yes. That is a "J" code distributor. If your engine has had overbore/high compression pistons installed, it is probably the preferred version. If standard pistons, it is still OK. The part number 353898R1 is just the distributor housing and is the same for most IH distributors.

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Re: bn magneto change out to battery ingnition

Postby Dave F. » Thu Mar 14, 2019 9:54 pm

Thanks Jim. Dave F.


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