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Onan GRCA Home Standby Gen


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  #1  
Old 10-10-2017, 01:09:02 AM
Steve Dawkins Steve Dawkins is offline
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Default Onan GRCA Home Standby Gen

Model: 12GRCA-4229A
Serial: J04870000317

I have some questions about the spark plugs for the Honda GX-670 engine on this generator. There seems to be some discrepancy between the Honda owner's manual and the Onan service manual.

The Honda owner's manual specifies NGK#ZGR5A plugs, gapped at .028-.031 inch. I assume this manual is based on the engine operating on gasoline. The generator can be run on LP or NG, but not gasoline. It is set up for NG.

The Onan service manual (184-0177) does not specify a particular spark plug, but does specify a spark plug gap of .012-.016 inch. The Onan manual indicates that the engine specifications can be located in the Honda owner's manual. I guess that defaults back to the Honda specified spark plugs?

We installed this unit 12 years ago. Since then, it has been maintained by two different generator service companies. The customer called me recently and said the company that he's had a service contract with in recent years informed him that they can no longer get Honda parts, and won't be able to service it any longer. He is very ill with a terminal disease and is confined to bed. I want to help him out so that he doesn't have to worry about the generator. I am not an engine guy, but have worked on my own vehicles, generators, and various small engines since I was a kid. I can do tune-ups and minor work, but nothing major, engine wise. (At least not on someone else's equipment.) I suspect that I will only have to PM this generator once for him, although I wouldn't mind doing it for longer.

Now for the questions.

1. Does .012-.016 inch gap sound correct? I have never set the gap this small before, but wondered if this was normal for dry fuels vs gasoline.

2. I don't know what the orginal spark plugs were. The current plugs are NGK#TR5 V-Power. The local Honda dealer gave me NGK#BPR4ES plugs. Are these correct or satisfactory for this engine? If not, what plugs would you recommend, and what gap?

As a side note, the the field report from the most recent service call in Jan 2017 indicated that the generator had faulted on overcrank. The tech commented that he found one plug gapped at .020 inch, and set both plugs at .030 inch.

Any insight you can give me on this issue would be most appreciated. Also, is there anything in particular that I should be checking/looking for that's unique to this model genset?

Thanks,
Steve
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Old 10-10-2017, 09:03:55 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan GRCA Home Standby Gen

To me this shows how far Onan has gone down in quality. They don't recommend a plug. Give you a gap setting. Then tell you to use the Honda specs. I would go with the Honda .030.
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Old 10-10-2017, 09:32:16 AM
Birken Vogt Birken Vogt is offline
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Default Re: Onan GRCA Home Standby Gen

The spark plug model concerns me a little bit. Both NGK numbers refer to a flat gasket seat. The TR5 is a cone seat like a flare fitting. I would remove the plug and look at the head surface and see if it is flat for a gasket or a recessed cone.

Otherwise I have found that performance is generally better on gaseous fuel with a tighter gap. I would run .020 or .025. It is not critical as long as the fire gets lit somehow.
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Old 10-10-2017, 12:34:29 PM
Wayne 440 Wayne 440 is offline
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Default Re: Onan GRCA Home Standby Gen

See page 25- this is for a propane/NG engine

http://cdn.powerequipment.honda.com/...s/31ZN1603.pdf
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Old 10-10-2017, 12:39:26 PM
Wayne 440 Wayne 440 is offline
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Default Re: Onan GRCA Home Standby Gen

for future reference
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Old 10-10-2017, 01:39:53 PM
Steve Dawkins Steve Dawkins is offline
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Default Re: Onan GRCA Home Standby Gen

Thank you for your replies. Wayne, thanks in particular for the Honda manual. I don't know if that manual for LP/NG engines was available when the genset was manufactured. It is dated three years after the genset was made. May be a later edition. Otherwise, I don't know how Onan would have known about the .012-.016 gap.

I called the local Honda dealer. They looked up the ZGR5A-4 and said it is available, but they don't stock it. They will have them in a couple of days, so I will exchange the BPR4ES plugs, and gap them at .016". Any recommendations otherwise?

This genset has had a history of sluggish starting, and tripping out on overcrank occasionally. Several things have been checked over the years including the gas pressure. The gas regulator has been replaced a couple of times. The gas installer I used for installations always used utility grade regulators. One of the service companies replaced that with a Maxitrol. Fast forward a couple of years, and it was having trouble starting again. The customer wanted me to look at it. I saw the Maxitrol, and recommended it be replaced. My gas installer put in another utility grade regulator, which has been in place for about five years now, maybe longer. When I go out to service the gen, I will check the gas pressure. I expect it to be 7-11"WC.
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Old 10-10-2017, 01:45:22 PM
Wayne 440 Wayne 440 is offline
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Default Re: Onan GRCA Home Standby Gen

http://cdn.powerequipment.honda.com/...s/31ZN1601.pdf

Here is the 2002 version.
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Old 10-10-2017, 01:51:41 PM
len k len k is offline
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Default Re: Onan GRCA Home Standby Gen

I'm not too good with vapor fuels but wasn't Maxitrol the demand reg that you used different internal springs for nat gas or propane ??
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Old 10-17-2017, 10:03:34 PM
Steve Dawkins Steve Dawkins is offline
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Default Re: Onan GRCA Home Standby Gen

Did a PM on the unit today. Birken hit the nail on the head. The existing plugs were incorrect. They were beveled for a cone seat. The cylinder heads have a raised shoulder with a flat seat. The specified plugs (NGK #ZGR5A-4) have the ring gaskets, and came gapped from the factory at .014". The existing plugs were gapped at .030". You can see in the photos that the electrode extends further on the new plug. When I exchanged the BPR4ES plugs, a side by side comparison showed about the same difference in the electrode length as the photos. The ZGR5A-4 plugs were more than double the price of the BPR4ES, but they are the ones specified by Honda.

Thanks again guys, for your help with this genset.
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Old 10-17-2017, 10:06:53 PM
len k len k is offline
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Default Re: Onan GRCA Home Standby Gen

Plug with longer insulator likely has a hotter heat range. On chevys we used to go up in heat range when plugs fouled, so extra heat would keep plugs clean.
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Old 10-17-2017, 10:58:08 PM
Birken Vogt Birken Vogt is offline
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Default Re: Onan GRCA Home Standby Gen

That is a projected insulator but not necessarily longer. The length is how far back into the shell it extends. Hard to judge by eye. But they are both heat range 5 so probably the same.

But it probably does not matter much running on vapor fuel. There are no gasoline deposits to burn off so a too-cold plug would probably work fine. A too-hot plug can always risk detonation but this is a generator we are talking about. Not a high performance race car.
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