cracked magneto cap

Charlie M

Well-known Member
I was rebuilding the H4 mag on my BN and cracked the cap covering the coil. The crack is on the back side of the cap. Does a crack in this area affect the way the tractor runs? I just got this tractor running
this spring and its still running rough. It had sat a few years with the previous owner. I haven't checked all possibilities yet as I needed too overhaul the mag before the tractor would start at all. The mag
was bought "as is" off ebay and needed a few things to make work.
 
The cap can leak water into the coil, I would sand the area around the crack with 60 grit paper, then apply a layer of JB weld to seal it. If not visible, 1/8" tick should do. Paint it black. Jim
 
(quoted from post at 12:52:05 04/28/20) I was rebuilding the H4 mag on my BN and cracked the cap covering the coil. The crack is on the back side of the cap. Does a crack in this area affect the way the tractor runs? I just got this tractor running
this spring and its still running rough. It had sat a few years with the previous owner. I haven't checked all possibilities yet as I needed too overhaul the mag before the tractor would start at all. The mag
was bought "as is" off ebay and needed a few things to make work.

One thing I would not use the JB Weld that has steel or iron in it on a coil cover, it could cause a high voltage short to ground.

New covers are available from the people who run this forum:

https://www.yesterdaystractors.com/Farmall-B_Magneto-Coil-Cover_47449DAY.html

I did check with NAPA online and it does not look like they carry those covers despite having all the other parts including the coil for the H-4 magneto on my BN.

The IH number for that cover is 47449DAY. I do have a spare but do not wish to part with it at this time. They are also available if you search that number on Ebay.
 
I was thinking eventually getting a new one - just trying to rule out for now the way the tractor is running. I think my used mag has been out in the sun a long time by the way everything is bleached out. I
have two tractors I have been working on this spring to get running and usable so I have been buying parts about every week. Wife's not too happy these days so I have trying to cut back a bit.
 
Mags do not have centrifugal advance. As a result they operate at full advance all the time after starting. The engines run ruff unless at full power. So smooth is not going to happen. Adjustment of the carb to smoothest is about all. To get smooth, you need to use a distributor. Jim
 
I have an A with a mag and it sounds a lot better than my BN does. My BN runs like it needs to be timed or the carb needs to be adjusted and changing them does have an effect but not enough. Tractor has a bit of black smoke like its running too rich but I haven't found anything to make it run rich. I haven't had the chance to check valve clearance and compression yet.
 
If the float level is too high it can lead to excess fuel. A check of the air cleaner for restriction (insect homes in the pipe, or dirty mesh above the oilcup, or hose coming apart might be good. Does it run better with the hose off the air cleaner to carb? Jim
 
the float maybe heavy or not set right. as for mags running rough I don't see that. I will park 2 w'6 one behind the other running then see if you can tell the diff. between mag or dist.
 
The float is set according to I&T manual. I think I remember 1 5/32 height. Its a Zenith carb. If you eyeball it looks level to the carb base. I haven't checked inside the air breather yet.
 

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