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ONAN 6.5 NH Rebuild + Conversion to Natural Gas


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  #1  
Old 01-04-2013, 12:26:40 AM
K-Tron K-Tron is offline
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Default ONAN 6.5 NH Rebuild + Conversion to Natural Gas

Greetings Smokstak,

A neighbor of mine, a family friend, purchased an ONAN 6.5N generator, a contractors model, for his house new in the late 70's. I suppose 1977 was the year the engine was made. When we lost power during Hurricane Sandy, his generator failed to start and operate. I went through the unit and found the points to be the problem. The spring was all warped and kinked and set way out of adjustment. With the existing points set as good as I could guess 0.018", the unit fired up and ran good. After about 6 hours of running he shut the generator off to refill, and could not get it started again. The fuel pump, carburetor to intake gasket and fuel line were all weather-checked and in bad shape from sitting all of these years. I replaced all in the dark of night, and had it running again for him. After that incident I was refilling his generator 4 times a day for 7 days to keep it running. The unit has a 7.5 gallon tank, and burns about 1.5 gallons of gasoline per hour. The man is in his late 70's and needs the machine producing power around the clock so he can breathe properly on his CPAP machine. I kept his generator running about 90% of the time over the course of our 9 day power outage.

When power was recovered, I brought the engine over to my house, made a new gasket kit for the carb, fuel pump, installed a new set of points, de-carboned the cylinder head, ultrasonically cleaned the carburetor, adjusted the governor to 1850rpm, changed the oil and regapped the plugs. The unit runs just about perfectly now, although it can really use new valve seals, and a valve adjustment as it is burning a small amount of oil. The oil is about a half quart low after 3 days of running around the clock.

My neighbor wants his generator to run as good as new, and hired me to do the work for him. I can rebuild the engine no problem, as I have done many Wisconsin, Kohler, Briggs engines in the past.

What I am not sure of is whether this ONAN can be converted to natural gas?

If yes, what is involved and is a kit available?
I presume it is just a carburetor swap out???

Is the output power of the generator enhanced or diminished by converting the unit to natural gas?

The unit powers just about his entire house and seems to do so without a hitch as is. I offered up the idea of converting it to Natural Gas to avoid waiting on gas lines and having to constantly refuel it. Refueling at 8PM, 2AM, 8AM and Noon every day is not fun!!!

Here are the engine/generator specifications:
6.5 NH-3CE / 2236D
Serial: J773281388
1800RPM
It is a 983cc opposed twin rated to produce 25hp

Attached are a few pictures,
As you can see the unit is in pretty good shape,




Thanks in advance guys,

Christopher Kouttron
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Old 01-04-2013, 12:29:21 AM
K-Tron K-Tron is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

All cleaned up,




And yes this unit has cylinder head shrouds. They just happened to be off in the above image.

Chris
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  #3  
Old 01-04-2013, 12:44:11 AM
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Jim McIntyre Jim McIntyre is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

Quote:
Originally Posted by K-Tron View Post

What I am not sure of is whether this ONAN can be converted to natural gas?

If yes, what is involved and is a kit available?
I presume it is just a carburetor swap out???

Is the output power of the generator enhanced or diminished by converting the unit to natural gas?
Yes, it can be converted. According to Onan Tech Bulletin T009, on gasoline a 6.5NH is rated at 6.8 kW maximum. On natural gas that rating drops to 4.8 kW. That's what Onan said, anyway. YMMV as they say.

Over here: http://www.smokstak.com/forum/showthread.php?t=113911
I reported on my natural gas mod to a 4.0 CCK. Since your engine displacement is 60 cubic inches ( compared to 50 for my 4.0CCK) I'd expect you'd get close to 6kW out of it after the conversion. You'll need to advance the timing when you switch fuel to get max power.

You'll need a fuel controller (aka regulator). I'd recommend a Garretson model KN available lots of places, including from these folks:

http://www.carbturbo.com/

They'll also have a 12V-operated 3/4 inch gas solenoid valve. That's pretty much all you need in addition to the carb.

You can swap the carb for a natural gas variant if you can find one, or modify the existing one yourself. Since this is for someone else, you might be best off to buy a 2nd gaseous fuel carb. (I don't know exactly what carb a 6.5 NH uses, but someone will be along to educate us both...)

BTW - Nice set - and 1/2 Qt of oil over 72 hours wouldn't bother me...

Last edited by Jim McIntyre; 01-04-2013 at 02:00:12 AM.
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Old 01-04-2013, 02:30:20 AM
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lokay5 lokay5 is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

I'm in the process of building an NH for propane. It originally was built with a Walbro/Onan carburetor, which can be drilled for gaseous fuel but it can no longer be used for gasoline.
I removed the Walbro and saw that there is an adapter bolted to the intake manifold. By removing the adapter a Marvel-Schebler (Facet) VD tri-fuel carbutetor is a direct bolt on, throttle linkage and all.
The M-S carburetors are scarce but they're out there.
Or you can drill a VD gasoline carburetor for gaseous fuel and still retain the gasoline function.
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Old 01-04-2013, 10:38:37 AM
lijobi lijobi is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

There are many conversions for propane and natural gas. Some are bolt on adapters and some are replacement carbs. One thing though, my CPAP machine has a 12v input and I can run all night on a car battery no problem. If no 12v input have him buy a small inverter. Charge the battery during waking hours when running other loads. Nice unit, a little maintenance and it'll be good for another 30 years. BTW, these are pretty easy to convert to electronic ignition and eliminate the hassel of points. Search this site for details.
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Old 01-04-2013, 10:48:43 AM
Ed Sparks Ed Sparks is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

Thanks for taking care to help out your elderly neighbor.
Does he have the manuals for his genset?
If not post an e-mail and someone will get them to you. Having the books always makes rebuilding easier.
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Old 01-04-2013, 11:39:57 AM
Max Thompson Max Thompson is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

Per Onan NH parts manual dated 7/1978, Spec. A-F the gaseous only carburetor is part #141-0838. The dual fuel part #141-0847.
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Old 01-06-2013, 01:05:13 AM
K-Tron K-Tron is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

Guys, Thank you so much for the input!!

All that I have at this point is an Onan operators manual which does not cover much of anything about the unit. I have found the critical torque specs and gapping measurement online which I have been using for reassembly.
If any of you guys have such information available in downloadable or email-able format, send me an email:
bigdogtrucker@gmail.com


Of the feedback so far, it seems that for my situation the acquisition of one of these Marvel Schebler tri-fuel VD carburetors seems like the best method for natural gas conversion. I do not have the generator at my house right now, but I believe the carburetor that it has was a Zenith model of some kind. On this unit there was no adapter between the carburetor and the intake manifold. From what I can tell, the VD carburetors are down draft carburetors, so I would need to get a different intake manifold, one with an intake manifold facing the sky, away from the engine, right???
If yes, does anyone know what the part number for the right intake manifold is?

Just looking online I have come across a few Marvel VD carburetors, a VD41, VD57, VD60, VD65, VD76 etc.
Any ideas as to what fits an NH series engine?
I see a few VD57's on ebay which are not that expensive. Will they work???

It is great to hear that these can be converted to electronic ignition. From the research I have done, it looks like I would need to order part number 160-1376 from Cummins/Onan. The conversion does not seem difficult, just expensive at ~ $185
http://www.gmcws.org/Tech/onan_elect..._ignition.html

Thanks again guys,
I have green fever too!! - I am a big 2-cycle Detroit Diesel fan.
It is going to be painful to have to purchase something from Cummins!!!
I do like the simplicity of this ONAN so far. They are rather similar to the Wisconsin engines I like to play with.

Chris
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Old 01-06-2013, 09:19:06 AM
Max Thompson Max Thompson is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

Service & parts manauls should be in your box.
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Old 01-06-2013, 10:43:34 AM
lijobi lijobi is offline
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Default Re: ONAN 6.5 NH Rebuild + Conversion to Natural Gas

There is a less expensive conversion and parts for the conversion are available on eBay new and used. Search this site and you will probably find about 3 ways to do it. Onanparts.com will have the parts and if you need to change the front cover eBay will have that too.
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