Onan OTC33 12V Generator No Spark Diagnosis

jimybuddiesel

New member
The onan engine spark plugs do not get fire. The contact points are extra clean.

There is small wire that is connected to the points. I am assuming that it is a kill switch, but was not sure if it may serve as an "exciter".

I separated the generator from the engine, and now I can not get fire to the spark plug. ( I was interested in the engine for another project and did not have any interest in the generator).

The engine ran great before disassembly, and I was able to start it with hand pull, without hooking up a battery (the generator design offered the option to hook up a good battery to start it, or to hand pull start the unit).

I have included a photograph of the assembly beneath the flywheel.

when I performed a continuity test, both sides of the points were ground to the engine, and I was not sure why.
 

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jimybuddiesel

New member
Re: ONON OTC33 12V Generator No Spark Diagnosis

My main question is whether the the plugs should fire with only a pull of the recoil starter, or if I need to somehow connect 12V positive to some portion of the ignition system.
 

cobbadog

Active member
Re: ONON OTC33 12V Generator No Spark Diagnosis

You should not need a battery to get that system to spark. It is a simple system and very similar to those used on early Victa lawnmowers here in Oz.
Check all your wiring and make sure none are shorting out. Not sure if you have a multimeter to check the condition of the condensor and coil but if it was starting and running easily before you worked on it there is a simple solution to your problem. Check your HT lead is made from a wire lead and not a carbon one. Clean and re-clean the points and gap them to 0.012" - 0.015". Is the timing correct?
Go through these things and if no joy take some better pics or do a diagram of the electrical system there clearly showing the coil, condensor, points and how the wires run.
 

jimybuddiesel

New member
Re: ONAN OTC33 12V Generator No Spark Diagnosis

I damaged the coil when removing the flywheel (village idiot), and want to be sure that coil is bad before I go to the next phase (low budget).

Testing coil: When I set the meter to ohms and place one lead on one of the two spark plug wires and the other on the base of the entire ignition module, I do not get any activity on the meter.

When I perform the same function on the "kill switch wire" and the base I get activity on the meter.

I also have three single cylinder Briggs coils on the bench to familiarize how the meter should behave.

In no instances do I get a static readout , the ohms measurement is dynamic and eventually zeros out. This is true even from a Briggs coil, that was from a running engine.

below are some photographs:
 

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gnucklehead

Subscriber
Re: ONON OTC33 12V Generator No Spark Diagnosis

D'oh (headsmack).. That there's a tough one.. Wico X3040.... Not an easy coil to find.

Make sure you are making good connection on the two plugwire terminals of the coil, and measure across those (6-12,000 ohms). The condenser is probably making your readings "dynamic".. disconnect it and make sure the points are open while testing the coil.

Maybe research spark alternatives for Maytag twins :shrug: Among OTC engines, the single-coil is a bit rare.. More common is the 2-coil configuration.

Q-Ed
https://www.smokstak.com/forum/showthread.php?t=131013

single coil
 

jimybuddiesel

New member
Keep in mind I am amateur as relates to voltmeter, but when I measure accross the two plug terminals I do not get an ohms reading.

Also, when I tested the coil, I had completely disconnected it from the points and condenser.

Again, no reading from the big terminals to the ground.

Separately, I think I found a single coil configuration, maybe from an Onan single (see photograph) in my warehouse, and i will try it to see if I can get some sort of spark from it. If so, this should eliminate some of the components, such as the flywheel and condenser as the issue.

Please provide a brief explanation of why I can not use a single coil, and splice two plug wires to it as the onan is horizonatally opposed and both cyclinders should be at top dead center at the same time. I am assuming that providing energy to two plugs simultaneously takes a lot of voltage/amps, thus the large coil.

Also, I am assuming that if I desire to use a battery, I can set up a standard external dual coil (such as from a Kohler or Onan twin) and wire it to the points to get the engine to run. Please let me know if that is possible as well.

The reference you provided about the alternative ways to modify the configuration with Maytag parts was way beyond my competence level, but it was interestiing trying to follow the conversion.
 

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AngrySailor

Subscriber
You cannot use two wires on a single coil as you describe, reason being they would be wired in parallel and the the spark will take the path of least resistance. If you look at the drawing gnucklehead provided the plugs are in series, with the ground (engine block) completing the circuit between them. The spark passes through one plug, through the ground, then the other plug for a complete circuit. One spark will jump from the electrode to the ground strap, the other from the ground strap to the electrode. This arrangement forces both plugs to fire regardless of slight differences in resistance.
 

gnucklehead

Subscriber
As I understand it there are four versions of that coil, the earlier ones are Eisemann and are what appear to be two coils "reverse" double-stacked (just like the schematic, one is upside down).. Eisemann went out of business (or was bought?) sometime in the 1940's.. Probably because their coils sucked.. The single-cylinder 1C and 1B engines from the day also have Eisemann points/condenser with the later models having a much improved coil (160B155 coil same as the the AJ).

Early Maytags
https://oldcroak.com/eisemann-72d-for-maytag-twin/

They probably went with two separate pole shoes (the OTC engine in Ed Stoller's write-up) because they needed larger coils :shrug: That flywheel has two magnets 180 degrees apart. Some 2-coil types have the points up behind the carb. Another configuration is like the CK, magneto-coil-driven spark towers.

If you can find two thin coils that will physically fit on one pole shoe, might work (it's something I'd try :crazy:).. like two of these ebay specials :shrug: ask the seller what the dimensions are.. install one facing in and the other facing outward.. otherwise, you'll need to replace the coil or possibly use the points/condenser with a battery ignition coil (Yes, that is possible)
https://www.ebay.com/itm/262831814496

Let me ponder this.. I do have a crapton of stuff in the garage. I don't like to give up magneto parts (especially coils), but I think I have a two-pole-shoe rig and a flywheel that you could add two larger coils to. If you are traveling this way anytime soon, I might be inclined to trade you one good OTC engine for your 12VDC generator head
 

radiodoc

Member
Couldn't tell too much from the photo(s). If just the insulation on the outside of the coil was chipped off and the mishap didn't get to the windings the place probably could be repaired with some layers of varnish. A coil can be simply tested with a 9-volt transistor battery and some clip leads. Just clip one lead to the HT lead on the coil and the other end to the HT terminal on a spark plug. Connect a clip lead from the metal of the spark plug to the laminations of the assembly or the common lead of the coil. Attach a clip lead to coil terminal going to the points and the other end to one terminal of the transistor battery. Attach another clip lead to the coil lamination assembly or common coil lead and momentarily touch the other end of the clip lead to the transistor battery. There should be a spark across the spark plug. I am sure if I have this all bass ackwards others on there will correct me.
 

gnucklehead

Subscriber
The older Maytag twins used the Eisemann coil, only the latest versions (small percentage) use the Wico.. I knew this last week, but I've been told that Zach's reproduction Eisemann coil won't work on a Wico pole shoe :(
 
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