520 with no spark

[truckin88 104]

Guys my dads 520 is in my garage...since it died and wont start...carb ia getting gas...I put new ngk plugs in...but it seems like a no spark issue...I used a volt meter with the positive on the wire and neg grounded, on crank I get 0.83v. The batt shows 12.99v...all fuses replaced..what can I teat and how....

Per the previous owner thw volt meter and fuel gauge dis not work. The others worked...my dad had about 4 successful hours before no spark.

Also it seems like it is not a safety switch...they qork as they should when their circuits are open the motor wont even crank.

[Foozerush 40]

Hang tight trucking, I'm sure an expert will chime in to help guide you.... I like to read up on onan issues to help me keep mine in top shape... Good luck

[Save Old Iron 1,571]

Will,

try this. I know you know electronics. The ignition module is nothing more than an FET triggered by a latched Hall effect switch. There are two magnets embedded in the trigger ring, one North polarity, one South. When the first magnet passes the latched Hall switch, the FET sinks the (-) terminal of the ignition coil to ground. When the second magnet passes the Hall, the FET is shut off and the (-) coil returns to 12 volts. THE COIL (+) TERMINAL SHOULD ALWAYS REMAIN AT +12 VOLTS - if not, you have a safety switch issue.

Never connect the black lead from the ignition module to a 12 volt source - doing so will destroy the ignition module.

click on image to enlarge

This whole process can be tested by engine off, key in RUN position. Test light should be bright on (+) and (-) coil terminals.

Move the test light to the coil (-). The ignition modules I have tested so far have powered up with the FET turned on. Soooo... you should see a few millivolts at the (-) coil terminal (manual says less than 1.5 volts - I have seen around 60 -70 millivots). While monitoring the (-) coil terminal with the light (or voltmeter) rotate the flywheel and within 110 to 120 degrees of crankshaft rotation, the second magnet on the trigger ring should turn off the Hall latch and turn off the FET. The (-) coil terminal should return to +12 volts (bright test light).

Of course if the engine cranks, you can perform the above test while cranking to see the +12 volt to ground to +12 volt transistions (test light should flash). If no flash, either the coil primary is open or the ignition module /wiring is defective.

Let me know. I'll be home late in the afternoon on Saturday if you need more help.

[truckin88 104]

SOI ty... I see 12 @ positive side and when cranking the ned side goes 0.89 to about 14v and back down...I am guessing the coil is ok?

[truckin88 104]

SOI ty... I see 12 @ positive side and when cranking the ned side goes 0.89 to about 14v and back down...I am guessing the coil is ok?

[truckin88 104]

Also what else could it be?

[Save Old Iron 1,571]

Will, try a temporary jumper wire between the battery positive terminal and the coil positive terminal - this will eliminate any funny business in the power to the coil circuit, Crank again and see if the engine fires. If not

Measure the coil primary resistance with an ohmmeter - should be between 3 - 4 ohms. Measure between the (+) and (-) coil terminals.

Measure between the two spark plug towers - this will be the secondary coil resistance - should be between 14k to 20k ohms.

Make sure condenser is present and hooked to the (+) ignition coil terminal - only the ign module black wire is hooked to the coil (-) terminal. Make sure condenser is grounded. A test with a replacement condenser can be conducted - Kolher points condenser will work as a temporary substitute.

[truckin88 104]

Soi ty...i will do it tomorrow am....should the key be in the on position when measuring reaistance. How am I sure the condensor is grounded?

[truckin88 104]

Soi with the ohm meter I am within those given specs on the coil and spark plug towers....i confirmed the condensor is hooked up properly...norhinf beyond that....where do we go from here? Still have to run a jumper wire.

[Save Old Iron 1,571]

Will,

make the connection with the jumper wire - this will eliminate all the possible issues with the safety switches.

The condenser is still suspect. A Kohler points system condenser can be used as a temporary substitute.

Just a recap

make certain the coil is wired correctly - condenser is on the POSITIVE TERMINAL

the 12 volts at the (+) coil terminal STAYS at 12 while cranking

the 12 volts at the (-) coil terminal toggles between approx 1 volt to 12 volts while cranking

coil primary measures 3 - 4 ohms

coil secondary measures 15k ohms to 20k ohms

a properly grounded spark tester / good spark plug shows no spark on either spark wire

[truckin88 104]

The wire from the condensor is going to the negative terminal thw one that toggles voltage when cranking...is that right?

[Save Old Iron 1,571]

Not correct - condenser to the positive terminal

sounds odd but it is true for the Onan's - condenser is on the positive terminal

[Save Old Iron 1,571]

Will,

I got your instant messages.

The condenser is now confirmed to be on the + terminal and the engine did fire up for 30 seconds and then stalled.

You also mentioned this progress happened after fussing with the spark plug wires. I would say visually inspect the wires for corrosion at the metal clips at the wire ends. Also check for corrosion inside the coil towers. Check the spark wire resistance while flexing them. The resistance should not vary while flexing.

The wiring connections to the coil need to be inspected closely. Possibly some corroded or broken wires inside the insulation of the wires to the coil.

[truckin88 104]

Soi...i order sp wires will update when they are in. The resistance of the sp wires seems to be all over the place...this 520 had problems after my dad replaced the plugs which i switched with new ngks...i have a hunch the wires could be the culprit...if they arent it is not a bad idea to change them.

[truckin88 104]

SOI SOI SOI!!!! Got the new plug wires put them on this morning, battery was dead so she needed a jump, but she started no problem twice (once with jump and once without) and ran great for a good 10 minutes or so. While running I noticed sparks from the underside of the silver rectangle metal box with 3 wires coming from it on top of the engine, I took a picture....not a ton of spark (almost like an arching spark), but one or 2 when changing the throttle position...and one or two ever minute while running (gas and spark is a scary combo outside of an engine)....as I seafoamed the gas at the same time, so I was running the throttle....What is this piece (voltage regulators?), what do the sparks mean, should anything be changed?

Also she won't restart not, even jumped, just cranks and cranks, is it possible that the battery is crap? When running on its own the battery was seeing 13.91V

thank you for all the help!!!

[Save Old Iron 1,571]

SOI SOI SOI!!!! Got the new plug wires put them on this morning, battery was dead so she needed a jump, but she started no problem twice (once with jump and once without) and ran great for a good 10 minutes or so.

You're Welcome - this is the biggest step forward so far. All those jumpy resistance readings from the old wires indicated the wires or connections were keeping the spark from reaching the plugs.

While running I noticed sparks from the underside of the silver rectangle metal box ....What is this piece (voltage regulators?)

Yes sir, that is the voltage regulator. This one belongs in the " there's a first time for everything" category - I have never seen sparks near a voltage regulator. However, the stator is producing nearly 40 volts AC on the two outer terminal connectors, so the grounded engine skins near a 40 VAC source can easily be a source of sparking.

what do the sparks mean, should anything be changed?

With enough voltage difference between the chassis tins (grounded) and the stator voltage on the white connector(s) on the voltage regulator (40 volts), current is flowing to the chassis tins instead of thru the regulator unit. This starves the battery of charge current and the sparking may be causing electrical "noise" on the 12 volt supply line to the ignition module. The result may be a "confused" ignition trigger and improper triggering of the ignition coil.

We have to make sure there are no conductive paths from the white stator wires on the RR to ground. I would cut off the two white terminal connectors and crimp on new push on terminals. I don't believe those connectors are original and that area may have been a problem for the previous owner too.

Make sure the regulator terminals are clean and free of any debris that could become a conductive path to ground. Also, remove the regulator from the engine and clean the area where the regulator attaches to the chassis tins / engine block. This is your ground connection to the regulator.

is it possible that the battery is crap? When running on its own the battery was seeing 13.91V

13.91 volts is not bad for a discharged battery under proper charge from the RR. I would top off the battery with a slow charge from an external battery charger and when the RR wiring is cleaned up, try to start the engine again.

Hang in there. I think we are getting close to finalizing this one.

[truckin88 104]

Should I replace the regulator?

[Save Old Iron 1,571]

Will,

I'm not yet convinced the RR is defective. 13.9 is OK for output into a discharged battery. The regulator voltage should rise as the battery takes on a charge.

New terminal connectors are the next step. There should not be any electrical pathway for the voltage from the stator wires to arc to the chassis tins.

Make certain there is an air gap between the terminals and the RR body / engine tins.

It is possible one of the terminals is broken and loose on the RR body. The terminal could be sagging near the RR body or chassis tins.

I'll be getting back from my visit down south later this afternoon if you need further help.

[truckin88 104]

Soi... looks like the white wire uninsulated female spade terminal under the black wire on the right was touching the tin and shorting causing sparks.... cleaned the terminals and put on elextrical tape so no more spark.... she runs good...output is about 13.9 while running. I do think she could use a new battery as she only works ofg jump and a tricke did not help...once jumped this tractor is a beast mowed with her today.

[Save Old Iron 1,571]

That's some great news Will.

I have to wonder if that sparking at the RR was sending confusing electrical "messages" to the ignition control module and firiing it at the wrong time. I would have loved to get an o'scope trace of the power into the module to check out that theory - too late now !!

Thanks for hanging in there and getting back with the final fix. This time it was fairly inexpensive - just spark plug wires and some electrical tape. I would get a new battery in there asap.