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Onan 75 ENT Ignition Timing


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Old 04-14-2018, 05:48:09 PM
Snowcatt Snowcatt is offline
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Default Onan 75 ENT Ignition Timing

The manual for my Onan 75 ENT L says total advance at 1800 RPM should be 40 degrees. That seems like a lot and I'm questioning the manual. Can anyone confirm?
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Old 04-14-2018, 07:17:05 PM
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Default Re: Onan 75 ENT Ignition Timing

That was the 385 class engine. For some reason I remember 36 on timing. I will see what I can find.
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Old 04-14-2018, 07:46:13 PM
Pauls12 Pauls12 is offline
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Default Re: Onan 75 ENT Ignition Timing

928-0121 Onan EN ENT Genset Operator's manual (10-1986) here is your manual if you don't have it.
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Old 04-14-2018, 07:48:52 PM
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Default Re: Onan 75 ENT Ignition Timing

It says it's for a Ford CSG 875-6005A (Ford 460 ci turbo). Thanks for your help,

---------- Post added at 05:48:52 PM ---------- Previous post was at 05:46:52 PM ----------

Thanks Paul, but Eric already sent that manual to me. I really appreciate the offer.
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Old 04-14-2018, 07:54:58 PM
Pauls12 Pauls12 is offline
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Default Re: Onan 75 ENT Ignition Timing

in manual 928-0121, it says 40 btc at 1800rpm.
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Old 04-14-2018, 08:02:19 PM
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Default Re: Onan 75 ENT Ignition Timing

Thanks Paul. That's the same manual I was looking at. 40 degrees seems like a lot but propane engines can take a lot of advance. Maybe that's right. I really appreciate your help.
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Old 04-14-2018, 08:04:19 PM
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Default Re: Onan 75 ENT Ignition Timing

The ENT operators manual, in particular, is what calls for the 40 degrees @ 1800rpm.

Timing for a generator engine, when compared to an automotive engine, won't have many comparable traits/features/adjustments. Automotive distributors get set with an initial timing, usually at an idle speed, and often had a vacuum advance module, in addition to the internal flyweights/bushings/springs. These items made up the characteristics of the distributor's timing curve--how it altered timing through a wide variety of engine speeds and loads.

On a generator, those features are not nearly as critical, as it is only going to run one speed during operation. And, often times, at a fairly light load. Air/fuel mixtures going through a lightly loaded engine will take longer to burn, and the engine can thereby utilize the greater advance to it's advantage.

The old-fashioned way to optimize your generator timing, that has always worked for me, is to be able to run the genset, set timing to any recommended spec, if available. Then load it up to about half of rated load, and with a vacuum gauge hooked up directly to manifold vacuum, loosen the distributor, and slowly move it back and forth to find the position that gives the highest vacuum reading. If you don't have a vacuum gauge, but have a multimeter that reads frequency, you can do the same thing to obtain the highest frequency reading (this frequency method only works with mechanical-governed engines, not electronically governed.)

Also, ensure all is right with the gas prior to tuning--properly sized components, piping, and correct regulator pressures.
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Old 04-14-2018, 08:11:04 PM
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Default Re: Onan 75 ENT Ignition Timing

Quote:
Originally Posted by EricWood View Post
(this frequency method only works with mechanical-governed engines, not electronically governed.)
Is there a simple explanation for this? I am not an automotive tech. by any stretch of the imagination.

This is why I love to hang out here at The Stak, I learn something every day. (too bad I can't remember it tomorrow )
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Old 04-14-2018, 09:37:45 PM
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Default Re: Onan 75 ENT Ignition Timing

Max,

With a mechanical governor there will be a perceivable, albeit small rise while under load, and making an adjustment that will result in optimal peak power output. That optimal setting would result in slightly more engine power, that would result in the governor being able to recover a fraction of the droop speed loss that occurred when the load was applied--this due to the power increase, that allowed the throttle to close a fraction, via governor response. The net result is that the droop characteristic of the governor hasn't changed, but available horsepower per kilowatt has increased, and this changes the amount of the droop curve used at a particular load level. In application, you'd be looking at pretty small changes; ie, say you started out with 59.1 hertz, and your optimal reading ends up be 59.3 hertz. With no load, it would be hard to see any change that way.

I simply offered it as an alternative...first choice should be to go out and get a vacuum gauge, if a person doesn't have one on hand.

The electronic governor is going to hold a constant speed setting, regardless, until the engine just runs out of available horsepower. More available horsepower per kilowatt would result in slight reduction of percent of throttle open, but speed would remain the same.
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Old 04-14-2018, 11:14:08 PM
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Default Re: Onan 75 ENT Ignition Timing

Interesting discussion. Thanks guys.
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