518H 18HP Onan

[Jess 29]

Pulled flywheel , took out 2nd insulator from module , Put tractor back together , started right up and ran like a champ ? Mowed for 1 & 1/2 hrs .  Never missed a beat the only thing is when I slowed I to idle it would surge a bit ?  I shut it off added fuel and it restarted !!!. This time it started to break up a bit on idle , but would smooth out  when I revved the engine .  The only thing I did different was I did not reinstall the flywheel perforated guard on the flywheel . Maybe allowed for better airflow ? While I had it apart this time I took a close look at the Black Rotor I ran a piece of metal over the outside of it where the magnets are and one magnet seemed real strong and the other was much weaker ?  Could this be adding to my mess ? or is this what I would expect to see ?  I cant believe how well it runs when it runs and to give me all these problems  !   I will order a new rotor and take it apart again when it arrives .

                Thank you for your time

    

[graywolf1939 24]

I have a new rotor on order also, the coil was bad on mine, secondary was open. I have a new IM installed also, and a new capacitor. The engine would crank over very fast, had plenty of gas getting to carb. and plugs are good, so that only left the rotor and weak magnets. If the rotor magnets are weak, there is no way the IM circuit will energize and allow current to pass through the Primary of the coil to ground .

[graywolf1939 24]

Jess, another point to consider regarding the screen guard over the flywheel. The danger of leaving this off is from grass and debris being sucked into the air intake and tube up to the air filter. When I cut my big lawn area up back (more like a field that needs a goat), I constantly have to lean over and brush away all the grass & hay that clogs the screen. I will bet that most of us have the same issue. This screen, when clogged sufficiently, and add in  a hot day out in full sunlight, and over an hour of constant mowing, the temperature rise on the Ignition Module must be quite high.

 

Save Old Iron, I have a new coil, ONAN part, 3.4 ohms on primary , new ignition module, original ignition rotor. When I used my test meter (clip to positive terminal on coil and probe tip to Negative terminal on coil, and crank over the engine, the light stays ON but it seems also to dim slightly (flicker) as it cranks. Could this be a weak magnet in the Rotor seeing this part was never replaced ?

 

ALL, I have built several computers and was thinking that maybe a closed loop liquid cooling system like the ones used in power computer that Gamers use, might be worth a try on my 518. The coolant line could be run against the IM if there is sufficient room, and this would certainly keep the IM cool under all load conditions.

 

[WVHillbilly520H 10,374]

Jess another often overlooked part of the air intake flow is the rubber gasket that fits over the oil filter to seal it against the engine tins, 1st pic my latest 520 WITHOUT gasket 2cd the Onan replacement,Jeff.

[Jess 29]

My rubber gasket over the oil filter is in place and I only left the fan guard off the test the machine .  When the new rotor comes in I will put it all back together , if it works right . Just that I have pulled the shroud and flywheel off like 10 times this week already . have to see how it goes as the rotor wont be in till next week some time .  I mow around 6 acers !

      thank yous

 

    Jesse

Edited June 10, 2016 by Jess
added wording

[Save Old Iron 1,566]

On 6/7/2016 at 5:05 AM, Save Old Iron said:

Trigger Ring Magnets

Magnets tend not to lose and then regain their magnetism in 20 minutes. Think hard, when have your magnetized screwdrivers ever lost then regained their power. Weak or marginal magnets installed in black trigger rings  during manufacturing - fine - that is believable. Losing and gaining magnetism - not sure anyone has seen that happen.

 

 

I need to add to this statement.

 

Although magnets do not lose and regain strength it is more accurate to say magnets can vary in strength when ambient temperature changes drastically (~10% lose in strength going from 32F to +200F). Less expensive ferrite magnets can vary much more than current day Neodyne composition counterparts. But once again, I do not know how hot the temps get around the trigger ring and module. If the magnets are barely adequate when cold and loose strength as the engine blocks heats up, and the ignition module looses sensitivity when it heats up, those two factors could be responsible for killing the spark. Marginal parts that fade in performance when heated - classic electronic ignition issue.

 

You say one magnet on the trigger ring appears to be much stronger than the other. A simple test would be to lay a paper clip and the trigger ring on a piece of paper. With one magnet in the trigger ring facing the paper clip, move the trigger ring closer to the paper clip until the paper clips jumps into the ring. Measure the distance it takes to get the clip to jump on one trigger magnet versus the other. I imagine they should be about the same. If you see a big difference, the trigger ring would definitely be suspect.

 

 

12 hours ago, Jess said:

Pulled flywheel , took out 2nd insulator from module , Put tractor back together , started right up and ran like a champ ? Mowed for 1 & 1/2 hrs .  Never missed a beat

    

 

Jesse, are you now running with just one thickness of gasket on the ignition module?

 

or none?

 

 

Edited June 10, 2016 by Save Old Iron

[Save Old Iron 1,566]

9 hours ago, graywolf1939 said:

Save Old Iron, ......   When I used my test meter (clip to positive terminal on coil and probe tip to Negative terminal on coil, and crank over the engine, the light stays ON but it seems also to dim slightly (flicker) as it cranks. Could this be a weak magnet in the Rotor seeing this part was never replaced ?

 

 

GW,

 

In a properly functioning module , the magnetic sensor operates in either a full on or full off mode. Think of it as a light switch in your home. Either you are able to move the toggle on the light switch enough to make it flip on or off. If you don't apply enough force to "flip the switch" it just doesn't do anything and stays in it's last position. There would be no half on condition due to a weak magnet. Remember, there are 2 magnets in the trigger ring, on turns the module on and the other turns the module off. If the OFF magnet gets weak, the module will never turn off. If the ON magnet gets weak, the module will never turn on.

 

The investigation I did for the bench test of the ignition module showed me the module seems to power up in the ON mode. So yes, the test light would come on when the ignition key is turned on. As the engine cranks. the trigger ring would turn the module on and off - thus flashing (flickering)  your test light.

If the tractor stopped running and you performed that same test while the tractor would not start, if the light did not flash as the engine cranked, the module is not turning on and off and therefore becomes the prime suspect of why there is no further spark.

 

 

This movie is worth watching. The small black transistor on the white perf board is what is located in the "nose" of the ignition module.

Pay particular attention when he describes the LATCHED version of this sensor. The magnet must be one polarity to turn on the LED  and the opposite polarity to turn OFF the LED.

 

Consider the blue LED that lights up to be the ignition coil. The magnets in his hand are the trigger ring and the black transistor looking sensor is the ignition module.

 

 

 

 

Edited June 10, 2016 by Save Old Iron

[Jess 29]

I I tried the 2 -1/16th insulation  first then the one and the only time it started was when I took both out . It will not start with an insulation spacer between the module and block . I even checked that I had good ground to the module tab and both screws and star washers each time .

  I have the machine back together and will take it apart when the new rotor ring gets here .

           Thank you

[cleat 6,397]

Just a thought but, if having any spacing whatsoever affects the spark then maybe, as the engine heats up, the metal expands slightly moving the module out then it loses sight of the magnets resulting in no spark ?

 

Is it possible that the rotor is just pushed onto the crankshaft just slightly too far ?

[Jess 29]

 The rotor is in a set position ? Just push it in till it stops against the shaft seal? I could make a spacer and put it in first before the rotor as to bring it out 1/16” th  Don't know know this would effect the overall running of the rest of it ?

[boomers_influence 106]

jess

you DO NOT want the ignition rotor pushed against the SEAL.

 

you want to just lightly install the rotor, and let the flywheel

push it into the proper location.

when this is done it rotates with the flywheel.

the SEAL DOES NOT rotate, so you do not want the rotor

next to the seal.

this makes sense because you are saying that it is better

without the insulator.

thank you. boomer

[Jess 29]

That’s where it was when I took it out or as far in as it could be ?  What stops it from moving where it wants to go when the shaft is turning ?  It seem as though it just sits there on the shaft . Nothing to lock it in place ? Maybe its worn that is why its like that ?

    Thank you

[WVHillbilly520H 10,374]

This is why pictures are worth a thousand words they usually show more than we can ever describe, Graywolf mentioned a "small ring" cut into the crankshaft where the trigger ring/rotor sets and had to "pry" out to get aligned before reinstalling his flywheel, I cannot verify as I myself have not had the flywheel off an Onan as of yet (mine went bad in a very high O/T situation at work so it went to a trusted shop), maybe Cleat or Boomers Influence or anyone else which Onan tear down rebuild experience can educate us on that and differences between production years and if in fact there's groove in the crankshaft for the rotor to not move in and out?...Jeff.

Edited June 10, 2016 by WVHillbilly520H

[Jess 29]

When I remove the flywheel all that is there is a tapered keyed shaft that the flywheel mounts on then the stator which has 3 bolts .  Once I remove the stator the ignition module is mounted with 2 bolts and the rotor or magnetic ring has a keyway so it slips on the keyed shaft and that’s it . I see the key holds it in place when spinning but what stops it from any in and out motion ?

  No snap ring or retaining clip or nothing to hold it in place on the shaft,  other then its keyed . That’s why I just assumed it finds its own place once its put in there ?  I don't know ?   Maybe someone has a picture of what its suppose to look like ?

  Thank You

[graywolf1939 24]

I can tell you guys from personal experience, the engine crank shaft has a very small slot cut into the shaft in which the ignition rotor outer edge positions itself. I discovered this when I was reassembling the flywheel the first time. I noticed that the large keyway slot on the ring was NOT lined up with the keyway on the crank shaft. I tried to move the ring (rotate it back) by my fingers and it would not budge. At this point I called my WH dealer who told me DO NOT grab with a screwdriver because it would break the plastic ring. So, I decided to carefully use a needle nose pliers to try and get it to rotate. I was finally able to rotate the ring to the aligned position. The the key fit into the large slot in the ring and the raised part of the key sat nicely into the slot in the crank shaft, and the key had a small rear amount of key length that would align with the flywheel slot.

As Jess stated, the stator ring mounts with three screws so there is no adjustments here. The Ignition module mounts with two screws, and there is absolutely no adjustment to be made here either. The only possible adjustment that can be made is with the insulator thickness. Obviously you can have minimum spacing with no spacer in which the IM is right up against the engine housing, and by adding more spacers, 1, 2, etc, you will increase the spacing that the pickup head has from the body of the engine, and therefore the Ignition ring magnet alignment. Perfect alignment would occur when the center of the Ignition module pickup head is dead center with the magnet/s on the edge of the ring.

 

GW, great info, love it. As for my test light that I bought at an automotive part (DAP) store, I hope it is Ok for this purpose (WH testing) I will do a current draw test this weekend to see if I am drawing in the range of 3 to 4 amps (12V/3.1 Ohms primary winding) which should indicate that the lamp being used in my light probe is not introducing an error (no ON/OFF that is clearly indicated when cranking over the engine).

 

[Jess 29]

 I did notice that when I took the black plastic rotor out the very first time , that on the inside outer edge there was like a worn little bead or roughed up plastic that I thought was just some wear on the ring from being in there  for 30 years . When I changed the ignition module last year I did not know anything about changing the ring as well . So I will be able to compare them when the new one comes in next week.  This could and hopefully be the fix I need ?  Like I always say when it runs it’s strong and still like a new motor . I have always babied this tractor and been garaged its whole life (HA)

    Thank you

       Jesse

[Jess 29]

Got my new plastic Rotor today and compared it with the old original , the only difference I found was that one of the magnets in the old black one was much weaker then the 2 in the new one . I did the paper clip test . There was no grove in/on  the shaft  and no grove in the outside for the new rotor to snap into or alien with . The only thing is the keyway and the fit on the tapered shaft . So I’m guessing the inside  I.D. of the old rotor must have been worn not allowing the magnets to line up right with the ignition module .  I ran it for over an hour and shut it off and restarted it 3 or 4 times and runs like a new machine .  I hope this is the final solution after a 2 year project !  A little plastic ring !  I took a couple of pictures to show you the shaft and where the rotor sits . Cant get the pictures to post ? It keeps telling me I only have 788.8KB

   Thank you all for your help time and information ! 

 

           Jesse

 

Edited June 16, 2016 by Jess

[Jess 29]

[graywolf1939 24]

I just received mine also Jess, I have been so darn busy here that I haven't had time to pull the flywheel off and change out the rotor. I did check the magnets in the new rotor and they are strong enough to hold an envelope opener knife !!! I will check out the old one hopefully on Thursday.

[Jess 29]

I hope it works out for you !  I wised I would have known enough to change out the rotor last year when I put the new ignition module in ! Would have saved a me a lot of time and aggravation ! But I guess it’s a learning experience  and it didn’t hurt to change all of these other parts after the 30 years of use I’ve gotten out of it. A lot of the  machines they build today are nothing like the old Wheel Horses !

[Jess 29]

My 518H is all back together !!   That was it the Rotor / Trigger Ring .  Now just weighting for my new Volt gauge and it will be whole again.  Mowed for 2 hrs. in 95 degree heat and stopped and restarted like a new tractor .   Thank you all for your input .

   Jesse

[Kurt-NEPA 755]

Yeah!  Congratulation Jess.  Perseverance paid off.

[Jess 29]

Thank you , 

 I lost tract of how many times I have pulled this thing apart ! But worth it when you see it finally run right !

[Kurt-NEPA 755]

Feels good, doesn't it.  BTDT!

[Jess 29]

  Yes ! Almost like I was back at work (HA)

Edited June 16, 2016 by Jess