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Onan Question


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#1 tweidman OFFLINE  

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Posted March 11, 2010 - 08:31 AM

Does an Onan opposed twin fire on every stroke like the Kohler twins? I was reading in my Kohler twin manual that every other spark is wasted on the Kohlers. :confuse:

#2 DH1 ONLINE  

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Posted March 11, 2010 - 07:48 PM

I think they fire once every revolution they have a single coil with 2 spark plug wires, and 1 wire that signals the coil.

#3 olcowhand ONLINE  

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Posted March 11, 2010 - 08:16 PM

Yep, they have a waste spark.

#4 Bill56 OFFLINE  

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Posted March 12, 2010 - 08:10 AM

This was interesting to learn. I've never worked on any two cylinder engines. I picked up a junk lawn tractor, last year, and salvaged the two cylinder vertical Briggs. Are they set up this way too?

#5 massey driver ONLINE  

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Posted March 12, 2010 - 09:44 AM

This was interesting to learn. I've never worked on any two cylinder engines. I picked up a junk lawn tractor, last year, and salvaged the two cylinder vertical Briggs. Are they set up this way too?

I believe that they do.On my Honda 20hp it's got two separate coils one sits at 10 oclock and the other at 2 oclock so each revolution of the flywheel will activate them to fire each time the magnet on the flywheel excites them.So yes they do have a wasted spark as well.Larry

#6 olcowhand ONLINE  

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Posted March 12, 2010 - 10:12 AM

All Briggs twins I've ever seen had waste spark & I believe they ALL do. Any engine without points produces a waste spark. The cam operated points only open the points on every other round, but pointless ignitions fire off the flywheel, so MUST produce a spark every turn of the crank....thus the wasted spark.

#7 tweidman OFFLINE  

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Posted March 12, 2010 - 01:51 PM

All Briggs twins I've ever seen had waste spark & I believe they ALL do. Any engine without points produces a waste spark. The cam operated points only open the points on every other round, but pointless ignitions fire off the flywheel, so MUST produce a spark every turn of the crank....thus the wasted spark.


I was guessing that the onans did not have points. Thx all.
I am just trying to figure this whole tach thing out. The waste spark is just throwing another problem into the mix.
My kohler also has two coils to further confuse the tach.

#8 Bill56 OFFLINE  

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Posted March 12, 2010 - 03:22 PM

All Briggs twins I've ever seen had waste spark & I believe they ALL do. Any engine without points produces a waste spark. The cam operated points only open the points on every other round, but pointless ignitions fire off the flywheel, so MUST produce a spark every turn of the crank....thus the wasted spark.


I didn't think about it, but it makes sense now that you said that... it has to fire that way. Thanks for explaining it.

#9 olcowhand ONLINE  

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Posted March 12, 2010 - 07:57 PM

You made me start thinking Todd! The later model Onan engines do not have points so definitely fire every revolution, but I think the point models do also, but I'd have to check a cam to know for sure if it has 2 lift spots for points plunger. Never had reason to check. The cylinders fire opposed, but pistons come up & down together. In any case, the Onan point models must have a waste spark being pistons come up together and only one side fires at a time. Maybe all point twins do! Hmmm....this is straining my tired brain! :rofl2:

#10 DH1 ONLINE  

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Posted March 12, 2010 - 08:20 PM

I think they fire (spark) every revolution. A single coil feeding 2 cylinders will spark both cylinders (at the same time) every revolution.
Pistons are at TDC at the same time but fire (power stroke) 360 deg. apart, every 2nd revolution.
2 separate coils can fire at 2 different times.
This is what I think.

Edited by DH1, March 12, 2010 - 08:25 PM.


#11 massey driver ONLINE  

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Posted March 12, 2010 - 09:44 PM

Guess then on the V-twin thats why two coils one at 10 oclock and one at 2 oclock but they still will fire everytime the flywheel passes the coil.So they still fire even on the exhaust stroke as well as on the compression stroke.Only on the exhaust stroke its a wasted spark as the gases have already been burnt up[or should have been].Larry.

#12 C Holmes OFFLINE  

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Posted May 12, 2010 - 05:56 AM

Onan's have points. Right in the front under a cover. I don't think they are wasted spark engines. Things like 2-stroke twins are for sure as most have no points and fire from an igniter coil.

#13 C Holmes OFFLINE  

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Posted May 12, 2010 - 06:34 AM

Not that it is important but Onan's are not opposed engines, they are "boxer or flat" engines, an "opposed" engine is one in which the cylinders are double-ended, with a piston at each end and no cylinder head. That should cause an argument but not meant to. Opposed engines are usually used in ships or aircraft. This is an example of an opposed engine configuration.
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