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Onan 20 hp Engine


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  #1  
Old 10-06-2011, 11:13 AM
wxyoung2008 wxyoung2008 is offline
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Default Onan 20 hp Engine

Earlier this summer I bought an old sears lawn tractor that runs well but was missing the belly mower for $60 simply because I felt I could always remove and re-use the engine....20 hp Onan with horizontal shaft and 345 hours on the hour-meter.

This weekend I removed the engine and low-and -behold it has electronic ignition (NO Points) and a dual coil. How the heck am I going to get that thing started.

Looking for a hi-level overview of what I will have to do to get this thing going now that I have removed it and cut wires.
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  #2  
Old 10-06-2011, 03:51 PM
Motorhead Motorhead is offline
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Default Re: Onan 20 hp Engine

You might want to post the question in the ONAN Generator postings. Give the mod and serial # of the engine.
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Old 10-06-2011, 08:43 PM
David K David K is offline
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Default Re: Onan 20 hp Engine

The 18 HP Onan in my Sears tractor has battery ignition. I am ASSUMING yours does also. You need to hook up 12v. positive to the positive side of the coil. Run the 12v. thru a switch (doesn't matter if its a key switch or a toggle switch) so that you can turn the ignition system on and off. Again I'm assuming that you didn't disconnect the negative side of the coil since the ignition system is engine mounted and you only removed the engine from the tractor....not the whole ignition system from the engine.

Pictures of what you have would help if my assumptions are wrong.

Dave
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Old 10-06-2011, 10:39 PM
tdarden3k tdarden3k is offline
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Default Re: Onan 20 hp Engine

Thanks DaveK
It is dark now but I will post the model number tomorrow and a picture of the engine. Everything is intact regarding the coil wiring. Thank you again for taking the time out to respond and I will post pics tomorrow.

I am not very good as this is my first time doing this so hopefully it is battery ignition. I went looking for some kind of electronic ignition module and found nothing !!!


wxyoung2008
tdarden3k

---------- Post added at 09:39 PM ---------- Previous post was at 09:37 PM ----------

that is looking for ignition module within the tractor housing
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Old 10-06-2011, 11:12 PM
sprkplug sprkplug is offline
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Default Re: Onan 20 hp Engine

If it is indeed an electronic ignition Onan, the "module" is located underneath the flywheel. There will be two wires wrapped in a flexible, (white?) covering coming out of the sheet metal at the top of the engine, on the flywheel side. I think one is red, and the other, white. This system was typically used on the "P", or Performer, Onan twins, although I have run across a couple "B" series twins that had it as well - unknown if factory equipped, or retrofitted in the field.

All of the Sears tractors I have seen had Onans with point type ignitions - but, I haven't seen everything. if it has points, they will be located on top of the engine, under a long, slender sheet metal cover, usually accessible by removing the air cleaner.

Regardless of the ignition type, (electronic or points), I'm betting it is battery ignition.
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Old 10-07-2011, 11:41 AM
tdarden3k tdarden3k is offline
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Default Re: Onan 20 hp Engine

Here are some pictures.... I could not find a model number anywhere.
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IMG00207-20111007-1022.jpg   IMG00206-20111007-1021.jpg   IMG00205-20111007-1021.jpg   IMG00204-20111007-1021.jpg  
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Old 10-07-2011, 11:57 AM
sprkplug sprkplug is offline
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Default Re: Onan 20 hp Engine

In your third picture, the one looking down on top of the coil, there appears to be two wires, together in a sleeve, coming out around the blower shroud. Do those wires go to the ignition coil? I do not see the points cover, and the ignition coil itself looks like the newer version, so it looks to me like it is electronic, battery ignition.
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Old 10-07-2011, 02:20 PM
tdarden3k tdarden3k is offline
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Default Re: Onan 20 hp Engine

Went out and removed the front cover. There are 3 sets of cables coming out of a stationary ring of coils that the flywheel spins around. 1 set of cables goes to each side of the coil. another set goes to the device and heat sink shown in one of the attached pics. The other set of cable wires go to the connector with the red wires.
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IMG00209-20111007-1249.jpg   IMG00210-20111007-1250.jpg   IMG00211-20111007-1250.jpg  
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Old 10-07-2011, 02:34 PM
sprkplug sprkplug is offline
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Default Re: Onan 20 hp Engine

The ring of coils is the stator-think alternator, as in keeping the battery charged. Nothing to do with ignition. In the first pic, there is a clamp attached behind the flywheel. It contains two sets of wires, one set in a black plastic casing, and one set in a white casing. The two wires in the white casing should be 1 black, and 1 red. Those are the two wires coming from the trigger module UNDER the stationary ring of coils you see behind the flywheel. You must remove the flywheel, and the stator to remove the electronic trigger module, if, in fact, it is bad. Do you know if the engine runs?
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Old 10-07-2011, 03:39 PM
Motorhead Motorhead is offline
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Default Re: Onan 20 hp Engine

Previous post at the end..."Do you know if the engine runs?"
I saw the label on your pictures and it said "Electronic Ignition".
I believe that the electronic ignition runs off of the alternator on the engine. Have you put a battery to the starter to see if you have spark? I wouldn't hook 12volts to the ignition until I tried turning the engine with the starter and see if I had spark.
My $0.02
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Old 10-07-2011, 08:05 PM
sprkplug sprkplug is offline
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Default Re: Onan 20 hp Engine

I can't see any harm in doing what Motorhead suggested. However, "electronic ignition" in this case refers to the manner in which the primary ignition circuit is opened and closed. There still must be a voltage source for the primary circuit, something for the electronic module to switch on and off.
You can have electronic ignition and have a mag, or a battery supply the primary, just as you can have point type ignition, with a mag, or a battery supplying the voltage.

The coil on that particular Onan has two smaller,(primary) posts. A positive and a negative, just like what we're used too on high voltage battery ignitions. if you look close, you will notice that those two posts are different sizes, as are the ring terminals on the ends of the red and black wires (from the trigger module), mentioned earlier. only one way to hook up the module, which is good as they aren't cheap.

That engine will require a switchable, 12 volt source supplied to the positive coil terminal to have spark. My only question is whether or not the engine wiring is still in it's stock configuration, untampered with over the years. Like I stated before, Onan coils and modules are very expensive.
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Old 10-08-2011, 09:45 AM
tdarden3k tdarden3k is offline
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Default Re: Onan 20 hp Engine

All
Yes I have both heard and had the seller of the tractor drive it around in his driveway. It runs. I will be trying the suggestions here and report back either today or tomorrow on the progress.

---------- Post added at 08:45 AM ---------- Previous post was at 08:36 AM ----------

What I plan to do is the "safe" way as Motorhead has suggested and see if I can get spark with my tester. If not I will add 12v to the + side of the coil as "Sprkplug" has suggested and see what gives. Thanks Gentlemen I will report back
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  #13  
Old 10-26-2011, 10:25 AM
abburns abburns is offline
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Default Re: Onan 20 hp Engine

This looks to be a Onan P220 very similar to a P218. I have one of each.
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