OT: Converting Onan genertor to CNG

Regal13 · Jan 24, 2012

I was hanging out with a buddy today because I've been briefly disabled from shoulder surgery--and he presented me with this question. He has a generator from a big 'ol motor home that he wants to convert from gasoline to run on natural gas. I have not looked at it that close, but I know it was new in 1987 and it is a two cylinder Onan--probably about the same engine as the 316 & 318 JD riding mowers had.

Is there any easy way to convert a small engine like this to run on natural gas? I assume the carb will have to be replaced, but is there some generic replacement for small engines? We were wondering if a small carb from a forklift might work...of course that would more than likely be for propane and for two more cylinders, so it was just a thought.

Is this project even worth considering?

Jim McIntyre · Jan 24, 2012

Yes, it can be done. You might spend some time reading here:

Onan Generators - SmokStak

Regal13 · Jan 24, 2012

Thank you, Jim! That site looks like the mother-load of info on onan generators. I knew somebody here would point me in the right direction.

moonlight machine · Jan 24, 2012

Regal13 said:
I was hanging out with a buddy today because I've been briefly disabled from shoulder surgery--and he presented me with this question. He has a generator from a big 'ol motor home that he wants to convert from gasoline to run on natural gas. I have not looked at it that close, but I know it was new in 1987 and it is a two cylinder Onan--probably about the same engine as the 316 & 318 JD riding mowers had.

Is there any easy way to convert a small engine like this to run on natural gas? I assume the carb will have to be replaced, but is there some generic replacement for small engines? We were wondering if a small carb from a forklift might work...of course that would more than likely be for propane and for two more cylinders, so it was just a thought.

Is this project even worth considering?

I would not bother with natural gas. I doubt you can raise the compresion ratio enough to use NG without losing a lot of power.

bob11x · Jan 25, 2012

I haven't done it personally, but it is a coming thing in the lawn + garden industry (again).

Here are a few of sites :

Generator Propane Conversion Kits & Natural Gas Conversions

ACME Alternate Fuel Systems- PRODUCTS

propane-conversions.com | Propane and Compressed Natural Gas Conversion

Small Engine Propane Conversion

Timw · Jan 25, 2012

The Onan CCK engines were designed to run on gas, NG and LP. Not sure about the newer engines.
I needed an intake manifold for a Miller welder with a CCK 25 years ago and a friend gave me one he had laying around that had an LP carburetor on it. The manifold was from the 50's 0r 60's. I made an adapter for it and put a VW carburetor on it! It ran great.
The Onans are tough engines IF you can keep oil in them and water out of the exhaust!

mixdenny · Jan 25, 2012

SmokStak is indeed where you want to read. I have a 6500 watt Onan running on natural gas, although mine already came with a tri-fuel carb. Many home made conversions have been done, and there are lots of photos on SmokStak.

Many of the Onan carbs have the boss cast on the side of the main body where the factory would attach the ng feed. It just needs to be drilled through and a second location tapped for a holding screw for a feed tube.

There is no difference in the carb for propane or ng use, the ng setup is actually easier as you do not need a first stage regulator, just a demand regulator. Demand regulators are readily avilable on eBay. If you are using CNG from your own tank, it would need a pre regulator also. A manual flow valve does the duty of the gas adjustment on the factory built tri-fuel carb.

Dennis

Regal13 · Jan 30, 2012

well, i almost forgot about starting this thread here after going to smokstak. Someone there already had a thread started on the exact same thing.

I did look at the generator closer and it looks like a 6.5 NH

It came from a 1987 pace arrow (i think)

I also found a few of them on youtube that are the same generator.

I think the primary purpose he wants to convert it to run on natural gas is so he can hook on to the city gas line--which always seems to work, even after the carnage of a nasty ice storm. Also, it will be cleaner and not leave the carb gummed up for lack of maintenance.

I wondered about the oil, too, as running from a gas line, it will never run out of fuel. Did they have an automatic low oil shut off?

mixdenny · Jan 30, 2012

Regal13 said:
I wondered about the oil, too, as running from a gas line, it will never run out of fuel. Did they have an automatic low oil shut off?

It should have an oil pressure cut off. It is a sensor/switch located on the block near the oil filter. A single wire runs up to the points box and grounds the ignition when oil pressure drops.

One of my Onans ( a CCKA) is a factory built industrial version designed for extended running with no service. It has a 9 quart oil sump! They would run oil field pumps and other unattended operations where they would only be periodically checked. The Onan 1800 rpm engines will go 5,000 hours between routine maintenance and many have not needed a overhaul until 15,000 hours.

My other engine is a 6.5 NH like the one you are working on.

Dennis

WranglerRouser · Jul 27, 2020

The company I work for is having a Retirement (going-out-of-business) Sale after 38 years and liquidating their entire machine shop. Lots of SOLID equipment with plenty of life still left in them including this DUAL-FUEL (gasoline or natural gas) Onan Generator-3 Phase (Lot # 277); they don't make them like this anymore! Know anyone with a need or room to give them a second lease on life?

ONAN 30 EK GENERATOR 30 KIL, 37.5KVA, SINGLE AND 3 PHASE, 7 DIFFERENT VOLTAGE SETTINGS, RUNS ON G

DDoug · Jul 28, 2020

WranglerRouser said:
The company I work for is having a Retirement (going-out-of-business) Sale after 38 years and liquidating their entire machine shop. Lots of SOLID equipment with plenty of life still left in them including this DUAL-FUEL (gasoline or natural gas) Onan Generator-3 Phase (Lot # 277); they don't make them like this anymore! Know anyone with a need or room to give them a second lease on life?
View attachment 295117
spammers eat shit and die here

I'm sure the OP has fixed his problem qty (8) years ago.
Every single post of your total (18) post count is the same spamming "we are going out of business"

We don't need your junk spammer.
.
.

michiganbuck · Jul 28, 2020

I just converter a 4-cylinder air cooled generator from NG to petrol fuel/gas. The carb lever was much the same and it was a simple change as everything fit even the hose to the air cleaner....engine runs great and I am thinking about having 110 and 220 outlets installed and perhaps a 3-phase buzz box.
Originally it was back-up for a retirement home.

Phil in Montana · Jul 28, 2020

Keep in mind on ng the kw will only be 60% of gasoline, and a lot harder to start cold...Phil

Jim McIntyre · Jul 29, 2020

^ 60%? Not so sure about that. I see my Onan, rated at 7.5 kW, and capable of 9 kW on gasoline put out full rated power on NG. In my experience, cold temps make virtually no difference in starting ability.

YES - you'll get less power with NG than gasoline, but I'd not assert it's 60%...

Bill D · Jul 30, 2020

I believe the big rigs running on CNG have much higher compression to run more efficiently. A compression ratio similar to diesel. You will have to have some sort of positive shutoff valve in case the carb sticks open.
Bil lD

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OT: Converting Onan genertor to CNG

Regal13

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Regal13

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moonlight machine

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Timw

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Regal13

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