H4 Magneto still won't fire

ccaissie

Member
Going through an H4 which just plain quit in the field. When checking it, no spark, and no impulse coupling sound.
Impulse coupling wouldn't be a problem while running, tho'. It was balky to start.
Also, checked the coil which had an open secondary winding.
Points were good, condenser checked out ok, ohm meter showed changing readings.

I think I've read every blog post here and elsewhere, and studied the Blue Ribbon manual, etc.

Disassembled it, and replaced the pawl springs which were pretty sad. One broke.
New coil, good readings on the primary and secondary. THE CURE!
New points at .013"
New condenser with good ohm meter readings.
Checked the Coil cover, perfect continuity from contact strip to coil wire.
Internal wiring looks good, no shorting indications.

So, setup in a vice, no cap or rotor, and a ground wire from the body of the mag to a new spark plug and wire. Perfect continuity. The plug wire is in the coil cover.

Don't you think by turning the coupling and getting the 'snap' I would get a spark? Can you find any flaws in this setup? I know I'm omitting the cap and rotor, but the coil should put out a jolt without that.

So, what next? I think I should have gotten a rebuilt, considering the cost and time so far.

Thanks, guys, I know it's something I'm overlooking.....

Colin
 

New points sometimes have a film of oil on them. Drag a clean piece of paper between the points to clean them. New condensors are sometimes no good right out of the box. Swap in the old condensor and see what happens.
 
Talked to a Mag rebuilder here in Maine. Said to sand the points a bit. Also he said .013" was a bit tight, so I opened them up to .015".

So, no change. No spark.

Checked the Bakelite washers for the condenser..look good. I have both wires, one from the points, and one from the coil attached to the condenser. That's what I remember in disassembly. Every drawing and photo I have is too murky to show any details on this. Where else would these wires go?

It just seems I have a short somewhere that's killing the spark. Damn.

C
 
Take the cover off the coil and try it with the spark plug wire right on the output terminal on top of the coil. Make sure you have the coil positioned at the correct degree so contact is made with the terminal in the cover when installed. If you do not get spark with cover off, I would unhook the coil and condenser wire so you can check with the ohmmeter to make sure points have good contact with points closed and that they are not grounded when points are open. Also, on the impulse, you can knock the dowel pin out and turn it around where the ends of the weights contact it as they wear a flat spot. Also, just touching up the tips of those weights to square them off makes them contact that down much firmer so they don't slip past before the spring winds up and coupler trips them.
 
Cleaned points, swapped old condenser in. NADA.

Condensers match in resistance readings...as they accumulate charge, readings change to infinite resistance.

Thanks,
C
 
(quoted from post at 12:31:30 08/07/15) Talked to a Mag rebuilder here in Maine. Said to sand the points a bit. . . .
Could you supply the name of that rebuilder so we don't use him?
 
No spark when eliminating coil cover. Points reliably work, contact closes circuit, opening them shows no continuity...no shorting.

C
 
OOPS! What is SO WRONG about his advice? The sandpaper? An ignition file (remember those?) is more appropriate, I suppose..... I will reduce a point gap if the
distributor shaft is loose, but this is not a loose distributor shaft.

I don't wish to disclose more info until I'm also convinced he's BAD>

C
 
Make sure the cam that opens the points is tight. If you turn the mag upside down so the impulse don't catch, the points should break close to where the magnet has more resistance as you turn it over slow.
 
so, check the wire that goes from the condenser to the points. As in take it out, and make sure there are no breaks in it. I have been stumped a few times by a shorted condenser to points wire.....................that applies to F4 and H4 mags............

PS: also a broken wire can cause the same issue, as in broken inside the insulation.............
 
With the test you did with points , that should have eliminated a short. The reason I said to disconnect coil and condenser is the primary of coil has such very low resistance it is hard to tell if points are making and breaking properly if you test with them hooked up. I have seen many a H4 magneto where someone put the wires in wrong at the points end and they ground to frame and that should show up with wire disconnected at the condenser end. Make sure condenser isn't shorted internally with your ohm meter also and that the grounding screw with the little gadget is making good contact to condenser outer shell.
 
Appreciate all the ideas. I got spark yesterday on the bench with almost everything removed. What I now see is the wire terminal to the points block has a damaged, funky clip on it, protruding high enough to contact the inside of the rotor gear cover. Testing with the cover off showed everything was ok, and made me crazy.

So, coil was bad, and gremlins intruded during reassembly. I have bent the clip back into shape, and I have spark. I also cracked the bakelite block slightly, so I used some (non-metallic) plastic cement to reinforce it. Now that the glue has cured overnight, it's time to reassemble, and I expect the shorting problem is gone. Spark is not huge, though, probably because of the slow turnover speed on the bench, so I'll report in later on the running of the tractor.

This whole thread, and all the other magneto threads and inquiries, has been extremely helpful, a collection of do's and dont's. At first I was embarrassed because the resolution has to be simple, but anyone searching for H4 magneto problems will find this thread, and all the valuable hints you've submitted.

C
 
(quoted from post at 07:06:59 08/08/15) Spark is not huge, though, probably because of the slow turnover speed on the bench, . . .
If your impulse coupling is working properly, you should see a good spark while bench testing. If it doesn't throw a good spark at slow speed, it will not start well
 
Yep, that was it. The wire end clip that hooks to the points was deformed, and when I installed the rotor gear cover, the clip just kissed the cover and shorted it. Got spark with the cover off, not when it was installed. There it was.

I replaced the bakelite block with a fabricated teflon piece, made it a bit higher than the reshaped wire end clip. It'll NEVER short out again.

Installed it, timed it, and I swear it didn't turn once before it started and ran beautifully. Startled me, actually.

So, it was coil and impulse coupling that were bad, and all the rest was assembly issues.

Thanks, all, for the chance to discuss all this, and find the solution.

C
 
[b:22eea7426e][size=18:22eea7426e][/size:22eea7426e][color=red:22eea7426e][/color:22eea7426e][color=darkred:22eea7426e][/color:22eea7426e][/b:22eea7426e][size=18:22eea7426e][/size:22eea7426e]I'd like to thank you.I have a 42' H with almost identical circumstances. This has been a great help. I believe each one of these repairs is a journey unto itself. I do not want to hijack your thread, so I'm going to start a new one. I am what would be best described as a practical man. You said something about wondering if the expense was worth it. That is me too. We have started from the same point. So please join me on the new thread. I'll post the link here when it's up.

http://forums.yesterdaystractors.com/viewtopic.php?p=7702250#7702250

mike in IL
 

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