Very Long Post About Magneto's

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Mag Man
10+ Years
10+ Years
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Joined: Mon Jun 28, 2004 3:34 pm
Location: Central NY

Very Long Post About Magneto's

Postby Mag Man » Tue Mar 03, 2009 12:54 pm

Hi Guys and Gals,

I can not say I have been around much lately, I had another Forum that I was a Mod On and as a lot of you know it can take a lot of time to read every post and Move, And Or, Edit, and such. But between that and being really Ill for over 8 months now I have not been around Like I should, I hope to solve that by putting this forum on my home page so it opens every time I do, LOL

I do not know a lot of you, and I do know and trust a lot of the older guys here, Like BD, John the cub owner,Cecil, Donny,Rudi, and a lot of others, And as far as they can attest I have never wronged anyone!!!!! Actually I have bent over backwards for some for warranty work that was well over the expired time I allotted.
I have recently been dealing with John with a magneto that I refurbished for him, That did not turn out SAD TO SAY Like he wanted it too. I really wasn't up to the challenge when he sent it but I took it on because he was one of my regulars.
This was one of these mags like stated in another post that just would not start his cub good that he has that turns over with a lot of RPM's . And I have told John anything I can do for him please let me know and it will be done. But he wants to try and figure it out on his own. I can understand that with shipping 11.00 each way.

OK so here I go with what I have been taught over the years by some really knowledgeable people.

# 1 A magneto Coil Can be tested with a cheap ohm meter, But a magneto coil is wound with solid copper wire starting at the core I have never counted but probably a thousand times, Then On top of that and in between there is a light like wax paper, After the inital winding there are thousands of tiny copper wires smaller than a hair on your head. wound up and hooked to the nub that would hit on the coil cover. These wires seperate over time and even on new ones because they are so small and brittle they can break the current can jump between the breaks and start and run pretty well untill they get warm then loose connection all together. Causing a warm or hot no start. also causing starting problems and running problems some time. Now I can test a coil with an ohm meter and it can read good but have this condition and cause problems Or a coil can test Dead.

# 2 Most people over oil there magneto's causing oil to get all over the internal magnet rotor under the coil core and thus causing spark and or no run conditions. It basically fills the air gaps with oil. A fresh rebuilt magneto or usally even an old mag does not need a lot of oil they run on brass bushing I use a coating of molly grease on them and it should last a very long time even if you do not see much lube there because of the molly property's.

# 3 as Donny stated in a post and Donny is very knowledgeable about mags probably more than I the faster they turn the more they generate. I have been burnt so bad by a few of my rebuilt on my test machine that I was unable to use the arm I got zapped with for days. and this is just at idle RPM's. I would like to see an external 6 volt coil do that.
So this goes on how the trip actually works. The trip on the magneto is there so when you are cranking the tractor it holds back the mag and spark so It can fire after TDC thus making it so it can not kick back and hurt the cranker , Thats it it is at the right pos so when it does trip and everything is working like it should that it spins over the lobe on the internal cam at the points giving it a good spark just as the pistons and rods start to make the downward turn. If it sparked just a hair BTDC that's when the cranker will get the kick back and some time broken bones or even hit in the temple and killed.
I am sure there are people here that will disagree with this theory but this is how I was taught it worked.

# 4 There are a bunch of little things that can be done to tweak a mag and 90% of the mags I have seen are not put together rite either the trip pawl springs are in wrong, Or lack of or in the wrong place brass washers, and other hardware that was made to go exactly in one position wrong. Points installed wrong with to much or too little spring pressure, and all sorts of funny things. Everything has its correct place for a mag to work correctly and efficiently,

# 5 this is the correct way to adjust a rotor. when you put the mag together there should be sufficient grease all around the rotor and pinion gear, If the pinion gear is worn so the teeth are sharp get a new one before it breaks the rotor teeth or skips. You put it back together with the markings in line with the rotor and pinion gear and a new cap or a very clean cap and run it long enough so you can see the black or grey or dark spots on the cap brass or aluminum where the rotor fires on it. then if it way off to the side you can move the rotor one tooth toward the center of that little tower trying to get it to fire in the center. and that's usually the only time you need to do anything with the rotor timing.

#6 Yes The internal rotor magnets can get a tad weak, They are not supposed to because of the way they are made, And as far as I know NO ONE can recharge them correctly!!! I have been told it would take a recharger the size of a house to recharge them . They were made to never loose there charge like a horseshoe on other mags. And IH or a company contractor made a special sleeve that I have to go around the magnet of the rotor when ever it is taken out of the mag body,IH says this is a must for the J4 and H4 magneto's I am sure that mags that were sitting for very long periods of time in one pos or allowed to sit in water and rust can loose there charge a tad. But a mag that gets used regularly should not loose magnatisim. and as donny stated the faster they turn the hotter they get.

#7 and lastly I guess when I see comments on do not ever buy a magneto off ebay it irks me a little. I sold magneto's on ebay and in my opinion they were darn good ones or what I said they would be. Now I can say that if I was to buy one I would want to know everything that was done or replaced and a gurantee in writing on that so I could send it back if it was not. Because there are alot of people that use fgood used parts,refiled points. half worn rotors and pinions and some that have never been taken apart and have had the bearings checked for tolerances and lubed and such specially when they say its been blasted, OUCH there is so much cleaning to be done on a blasted mag thats its unbelevable where the media can get too, LOL I do it on some but they get cleaned about 5 times untill I am sure there is nothing left that can harm anything. alot of times its easy for me to use at least $10.00 worth of carb cleaner, Clear, Rags ,dremel tools, not counting all the electricity, Wood, and other things it takes to run a shop and yep I still only get $50.00 to do a complete rebuild on a mag with parts of course, But I like to replace as many parts as I can possible afford or need replacing to make sure I can warranty my mags, NO I would need probly $250.00 to do a complete rebuild with all new parts at todays prices but 75% of the guys out there can not afford that, So I reman them to good working specs with all new tune up and or coil but you will know what has been done or not done. I would never say I put a new coil in and not. Or use used Parts unless they were trip springs and were good. and if a rotor is not good enough for me or you you will get a rebuilt or new depending on what you want to spend, Like I said earlier I want to replace the points, Condenser , Cap , so if it comes back I know where I am at and not chasing parts that were used trying to figure out what went wrong and then that way they hardly ever come back also. :wink:

So I guess thats my little rant here, Thanks for listening and I hope you may have rec something that you did not know out of this. BTW I did my first magneto as a teenager when my Father died, I had no choice but to either learn the trade or have tractors sit here getting seized up by weather cause they did not run then I took advanced auto mechanics with my main task there being all mostly electrical. From turning coms on starters to completly rewiring a pickup that had burnt. But then again I did miss out on how to rebuild a ford transmission by doing electrical, :( But I guess it has paid off. LOL

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