H4 Magneto

[john connell]

I bought a '41 Model M that was kinda running but not hardly. After checking many things I came to the conclusion the problem must lie within the Magneto. I found some very good information on Youtube and began to feel confident with a tear down and see if i could find what isnt working right. Low and behold, I did find that one of the springs from the centrifugal weights had come off so the weight would not contact the post properly and I thought, therefore there would only be two chances for spark to go to the cylinders. Put it all back together using grease rather than relying on oil as originally intended. That meant that I needed to open, clean and replace the rotor gear drive. When opening it I wish I'd have taken extra attention at the setting of the mesh, whether R or L. Im now assuming that the gas powered tractors were all right hand turning because I think I heard that the Diesel tractors and stationary engines were all left hand but cant remember who said that. I know that sitting in the seat, the crankshaft direction is CCW or Left and the Magneto drive is CW or right turning but then the rotor gearbox changes that to CCW through the gears. So, I'm confused and am hoping that someone can fill me in on what is what. I pulled the cover off the points at TDC and found that the points fiber block was exactly midway between the high lobes of the shaft making me think that resetting the rotor gears would advance the rotor so that the points would be open as I should be getting spark on #1 cylinder right now and am not. Make sense to anybody. If so, please reply. Greatly appreciated. John

 

[teddy52food]

Line it up with the R.

 

[rustred]

the rotor must be turning clockwise when viewed from the back as with all engines. dont use grease on the weights. oil them. watch when the
mag trips and have a straw in the cyl. and verify its actully tripping at tdc on compression.

 

[F-Dean]

Remove spark plugs, the valve cover and the pan (You'll be surprised what you find!) to determine TDC and set points accordingly.

 

[john connell]

(quoted from post at 23:31:48 12/07/20) Remove spark plugs, the valve cover and the pan (You'll be surprised what you find!) to determine TDC and set points accordingly.

I really appreciate your reply, F but don't know what I can learn from looking at the crankshaft. I'm guessing that the #1 connecting rod in the center of the crank is what you're referring to. Is there more. I'm thinking that the mark on the front pulley will be in line with the indicator and that both valves will be closed, but what else. I expect removing the spark plugs will make it far easier to be exactly at TDC but is there more that I don't know. I'm delighted to have your help as I believe there is always so much more that I can and need to learn. Again, thanks for your help.

 

[john connell]

Hey Red, I got your reply and I'm lost. I don't understand the function of the magneto well enough to know how to identify when it trips other than by ear. When its open, of course, I can see it happen but how can I know when it's closed up. I'm not getting spark at all right now and maybe that means more than being just out of time.
I'm fascinated by the device but still can't understand how spark is created. Apparently current is being built up until one of the weights contacts the post and at that time, the current is released and travels to the rotor. One of the springs was not attached when I took it apart. I'm thinking that this would only allow two plugs to fire but I was getting spark at all four when running (running like crap). But I'm thinking that spark was jumping around inside the cap to different plug wires and resulting in only two actually getting spark when all four were supposed to be hitting. Am I making any sense. Have you ever encountered this situation where one weight was just floating around? Any other ideas?

 

[john connell]

Thanks Teddy. Thats where I'm at and appreciate your reply. I went to an auction last week and saw another M like mine but the magneto was sitting at about the 10:00 position where mine is about 1:00. It made me wonder how he even got that much adjustment out of the slots and what would be the reason for being so far out of the original location. The magneto drive seems to be something that isn't subject to any alteration at least without engine disassembly so being this far out of what I expect would be correct really makes me nuts. Can you think of anything that I'm not taking into consideration? Maybe I'm off by one tooth on the gear. Would that make enough difference to make it so far out of time that you'd never see spark? Thanks for your help.

 

[teddy52food]

You need to be getting spark before you put it on the engine. There are different
drive cups & that may be why his is different.

 

[teddy52food]

Once it is running, those flyweights are not doing anything.

 

[john connell]

(quoted from post at 03:49:48 12/08/20) You need to be getting spark before you put it on the engine. There are different
drive cups & that may be why his is different.

Can you describe to me how I can duplicate the engine drive while on the bench.

 

[Janicholson]

The impulse coupling is a starting aid only. This (and many) magnetos generate internal electricity by spinning a moving magnet (rotor) inside windings of copper
wire, called the "primary windings". The fact is that when starting, the magnets move so slowly that the spark is weak. The impulse coupling works by holding the
rotation of the magnet allowing a spring to wind up. As the rotation of the input shaft continues, it reaches a trigger point that Snaps the rotor forward making it
spin mush faster for a few milliseconds. This speed increase boosts the electricity generation in the windings I mentioned. This electricity is low voltage!
somewhere between 6 and 14 volts. This internally generated voltage is grounded on one end to the Mag, and the circuit through the windings is completed through the
points to ground again. This voltage driven current saturates a second set of windings(with far more turns of fine wire) in the upper part of the Mag with magnetism.
So at this critical moment, there is high current (maybe 4 amps) flowing in those primary wires making magnetism in both primary and secondary coils of wire.
The moment the Spark is to be delivered to the engines plugs, TDC in this case, the points open breaking the circuit in the primary winding. The condenser (it is also
in there, a round silver looking tube with a wire going to the points) absorbs some electrons keeping the points from arcing and burning out, and providing a bouncing
action with the electricity in the primary coil. This whole crisp event collapses the magnetic field. This collapse is radical, and as it collapses, the lines of
magnetic field (remember the magnet under tha paper with iron filings) produce high voltage in the secondary windings that voltage builds up until the gap at the
sparkplug (closest point to ground) is jumped. This might be 12,000 volts! The primary may have as much as 200 volts generated in it as well. These voltages bounce
back and forth until the energy is lost to resistance and the heat of the spark in the cylinder. Spark jumping may last 3 to 8 milliseconds at the plug, igniting the
fuel in that cylinder. After the engine starts (probably gets to 350 rpm) the impulse coupling governor weights move outward and prevent the catching of the rotor.
But now the speed of the rotor on its own can generate enough magnetism to make the spark. So it no longer operates.
One last thing ---- the timing (in this mag) is set to trip the impulse coupling at TDC, but when running the mag operates at full spark advance, making power and
efficiency. (with some limits) the TDC tripping of the impulse coupling prevents a hand cranked engine from firing adhed of TDC which will spin the engine backward
and injur the person cranking, The limit I mentioned is that gasoline engines like different timing at idle than full power. This mag has no way to do that, a point
and coil distributor system does do that and makes for a smoother running engine at all speeds. Jim

 

[Janicholson]

Yes. The drive is a disc with a projecting drive dog sticking out across the diameter. A drive to make it turn can be made from a short piece of 3/4" pipe welded onto a
bolt, at the head of the bolt (straight). Cut a slot in the pipe opposite the bolt to fit the mag drive. Use a variable speed drill, or an old 1/2 inch drill, and use
it to drive the mag. Put the mag in a vice (with wood buffers) to hold it while turning it. Spark plugs should be attached, and the body of each plug should be set on a
piece of metal that is grounded to the mag (body, not the kill screw) with a wire. They make enough energy to pee your pants!! Firing order front to back is 1342.
Point setting at the high point of the breaker cam is .013" Clean the points with a folded dollar bill before putting it together. You have the R/L thing under control.
The mag should not be turned backwards! It turns CCW looking at the drive plate. Jim

 

[john connell]

Jim, this is a wonderful explanation of the operation of a magneto and I'm forever in your debt. I begin to understand why the distributor came along to replace such a wonderful invention now that I'm understanding it's limitation of a centrifugal advance system. So when I shut the engine down and I hear the weights contact the pole it is happening simply because of the engine speed has decreased that much and they aren't "active" while the engine is operational. Makes me think that I've probably done damage to a working magneto. Well, I'll again disassemble it and see if I can find any reason for it not producing a spark and then see if I can verify that the timing indicators on the front pulley are indeed correct and try all over again. Thanks for all the work you put into your explanation. I can much better understand the evolution of the engine timing in relationship with the electrical timing. Truly fascinating how those guys put it all together so many years ago without all the gadgetry we have today.

 

[john connell]

Incredible! Thanks very much. I'll work on putting this all together in the morning and can't wait to try it. I've always been so impressed with how these old tractors can seemingly start on the first revolution of the crankshaft and how it's attributed to the voltage of the magneto. This will be fun. I feel like the magician just whispered his secret to me and now I know how to do the trick too.

 

[Janicholson]

You are welcome. I am a University Professor, and put effort in being understandable. Part of the Job. I find the forum here to be rewarding. Jim

 

[Janicholson]

Keep the rotation under 1000 rpm. Mags and distributors run at 1/2 crank shaft speed! Jim

 

[john connell]

If you're teaching a class in tractor mechanics, where do I sign up?

 

[gene bender]

The rotor turns right you need to set the gears so the rotor is lined up with the tower on the cap Make a mark on the body of the mag where #1tower is so you can turn the mag over and rotor stops at that position before the impuls fires. Now make sure the engine is on #1 compression. Install the mag with rotor point at the mark you are either on compression or 180 deg out Before installing mag have it on a vice with cap and wire and plug turning mag over does the plug fire if so you are ready to install and the engine will fire and start. I put the mag inthe vice an cap with all four plugs hooked up then using batt drill i can turn mag at different speeds checking fire at all plugs

 

[teddy52food]

It turns CW , not CCW!

 

[teddy52food]

Good explanation, Jim. Lots of free energy involved too.

 

[john connell]

Gene, and all the rest of you guys, THANKS SO VERY MUCH. I cant believe all the expertise you are willing to share. Makes me so happy that I share a common interest with such incredible minds. Im sure this comes from your experiences from many years and I thank you immensely for allowing me to share in your knowledge.

 

[Janicholson]

CW from the drive end, and that is where he will be looking. Jim