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graywolf1939

518 still will not start !!! Grrr

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My 518 bought new in 1988 started having electrical problems when hot (typical coil/ignition module issues) so I replaced both. The coil was bad, secondary was open, but while I had the flywheel off I cleaned the engine, replaced the ignition module, but not the ignition ring as it looked fine. After the parts arrived, I installed the ignition module and made sure the ring (which had moved while removing the flywheel) had the key-way lined up with the new key on the crankshaft, and installed the new coil. Engine cranks over fine, carb is getting fuel, no spark to plugs. The test light lights when on the neg. terminal of the coil and dims when cranking (stays dim while cranking, I cannot see pulsing action. The test light on the positive side of the coil is lit and stays lit while cranking dimming slightly.

  I pulled one plug and checked for spark while cranking...nothing, no spark on a good plug.

The new insulator "IS" on the back of the ignition module.

Can the ignition ring be bad? If so, how, it looked fine, no cracks, no damage noticeable.

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Could very well be was it the BLACK ring by chance? These are prone to weak magnets vs the GRAY but when my module went south I was advised to replace All components at the same time, "Jess" has a post going right now with his 518 also, try PMing BOOMER the Onan parts guy here,Jeff.

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Hi Jeff, yes, I seem to remember the ring WAS BLACK because it had slipped around on the crank shaft about 90 degrees when I removed the flywheel, so I had to slip it back to align it to the key-way slot. Damn......now I have to take the whole doggone shroud etc etc off again, pull the flywheel, etc to check out and more than likely replace the ring.

   It would make some logical sense that the magnets may be weak because as I check the negative side of the coil with my light tester, the light dims but has what seems to be a very weak flicker. If the magnetic pulse is too weak, the circuit in the module will not produce a solid ground for the primary of the coil. Without a strong current in the primary of the coil, the secondary of the coil will not produce a high enough voltage to cause a spark jump in the plug electrodes. I guess I know what I will be doing tomorrow morning !!!

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Sorry to be the bearer of bad news ,reckon I was lucky to have spent more $ first go around than tear into it 2-3 times, but lessons learned help out the next time or fella in need,Jeff.   This is my original 1 i don't know of any way to test it but my Tech guy said if the module goes bad this isn't far behind save yourself some troubles and put it all in together so we did.

IMAG2139.jpg

IMAG2138.jpg

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How did you pull this ring out Jeff, it seems as though it sits in a groove on the crank shaft. As for testing this little devil, I am going to see if I can use the old module and the old ring to build a test set up. If you look at the schematic of the ignition system, when the spinning ring with it's magnet comes in line with the pickup head on the ignition module, the circuitry inside the module produces a ground for the primary winding of the coil completing the electrical circuit. This allows the current flowing in the primary of the coil to produce a stepped up high voltage in the secondary of the coil and ultimately the spark at the plugs. Curious minds want to know...LOL

Cheers,

 

Dick

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Graywolf I got frustrated when I had the infamous run for 20 minutes and shutoff ect throwing parts(coil carb kit/cleaning) that I threw in the towel 7-8 yrs ago loaded the tractor up took it to the shop and said have at it (I was working 6/10 hr shifts and didn't have time for it then) but from every one else's post I believe once the flywheel is off the ring just slides off the crankshaft with the biggest "notch" as the keyway and this keeps it spinning with the crankshaft behind the flywheel, I'm pretty mechanically inclined but just didn't have time for it back then,Jeff.

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Good evening Jeff, when I had the flywheel off a few days ago, the ignition ring was really stuck because I had to try to turn it back about 90 degrees to get the key lined up on the shaft before I could place the flywheel back on. It was really stuck on there after 28 years. I finally got it turning, and it does sit in a small groove cut into the drive shaft, that is why I asked if anyone had taken one off. I don't know if you have to pry it up out of the groove, or some other technique. I think Boomer will know, he must have changed out many. I didn't get a chance to take things apart today, the grass was too long after yesterdays rain so I had to use the walk behind and you can imagine how long it takes to cut over 1 acre.

Cheers,

 

Dick

Thanks for the info RubyCon1, that is a neat way to check the IM, and the trigger ring magnets also. According to another post, I forgot who, but they said a flat blade screwdriver held between finger and brought close to the ring should be able to support the screw driver if the magnets are still strong, otherwise replace the ring.

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I would suggest checking the other 518 Onan post by Jess ,going on right now "Save Old Iron" has some really good trouble shooting tips and explanations for/about the IM coil and trigger ring,Jeff.

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SUCCESS !!!! Replaced the black ignition ring with a new one (Gray) strong magnets, and the beast roared to life !!! Just to sum up the problems, the coil secondary was bad also, open winding. The ignition module may be still OK, I will check this out later on the bench to see if the circuit will operate with a makeshift tester. Now the H518 has a new capacitor, a new coil, a new ignition module (and heat shield spacer), and a new ignition ring. The former parts lasted 29 years, so if these new parts last that long I will be 102 years old and probably won't even be able to mount the horse any longer !!! LOL

As a side note, after removing all the parts to get at the ignition module and ignition ring, as well as the coil, I can now do this blindfolded, sort of like field stripping my old M14 from Army days.

Thank you to all who contributed some really GREAT information regarding this problem, may you all win the lottery !!

Dick

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Great! You got it going, Mine is still running like a champ ! Cant believe that little plastic ring was such a headache !  I got my new Volt gauge today and installed and also changed oil & Filter while I was still on it .  That was it my original SW gauge was defective . So at least now I can keep an eye on my charging system again .
     Have a great summer !
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I cut my first lawn yesterday since repairing the ignition issues, it sure felt good to have this great tractor running well again. I also have to change the filter and oil soon. The weather has been great here in MA, all the bad storms have been going south into the Middle Atlantic states, and other fronts have gone into the northern New England states, however we are very dry, lawns are turning brown and we need to water the garden every day, luckily we have an artesian well.

Hope you have a great summer also and safe from Tornadoes

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No storms here in Mid MO but we sure do need some rain! This is or 15th day that we have been above 90% and heat index of above 100 ! Have to water the garden every day ! Have a deeeep well ! The farmers are having a hard time with their crops and lack of water ! Last year a lot of them lost their crops do to flooding . One extreme to the next ! But the mowing has slowed down (HA)   Glad your machine is running well !
   Stay cool
   Jess

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