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Onan 6.5nh propane conversion
By jgnat1488, Section Mechanical Posted on Sat Sep 27th, 2008 at 11:04:36 PM MST
Hello all,

hello all,
I have been a lurker here for some time but this is the first time posting. After seeing the onan on otherpower.com and not being able to get carb parts any more, I figured i would attempt to convert my 6.5nh to lpg. I used the lpg components from a toyota fork lift that was getting crushed at the local scrap metal yard. Keep in mind that this is our only generator and we are OFF GRID!! I took some pics and a short video. The video is on youtube. I hope the pics come out ok on the post.
First is pic of demand regulator and lpg control valve.

Top of mixer.

New switch for sellecting lpg or gasoline. Up lpg, center off, down gasoline fuel pump. The carb is still intact with the exception of the choke plate.

Side shot showing the tank and high press regulator.

The mixer is just a couple of the fittings that came with a kit from lowes for lpg/nat gas appliance flexable pipeing. You know the yellow flexy stuff for the stove. Let me know what you think!
Jason Gnatowsky
Heres the YouTube link: http://www.youtube.com/watch?v=zEnCMNP_PpE
TW

Onan 6.5nh propane conversion | 12 comments (12 topical, 0 editorial)

Re: Onan 6.5nh propane conversion (3.00 / 0) (#1)
by Rabrsniver on Sat Sep 27th, 2008 at 05:52:02 PM MST
(User Info)

Hi Jason,

Good use of recycled parts.

The only potential problem I see is that you've used a BBQ regulator between your tank and the demand regulator.
From my searches on the web that is a bad idea. Can't remember why exactly.

Look at http://www.propane-generators.com/ I think maybe that's one place I saw it.

Maybe you can just remove the guts (diaphram and spring) if you don't have a hose that will go directly from the tank to the generator.

I have used one of their kits on my Honda generator. I also have an Onan 6.5NHD which was factory converted to propane.
I also recently bought a kit for an old Onan 4.0 RV generator that looks a lot like yours. Always good to have a spare (or 2) if you're totally off-grid like we are. I picked this one up for peanuts.

John

Re: Onan 6.5nh propane conversion (3.00 / 0) (#2)
by Rabrsniver on Sat Sep 27th, 2008 at 05:56:32 PM MST
(User Info)

Jason,

On second thought, maybe removing the diaphram from your high pressure reg. isn't the way to go.
Its been a while since I did my conversion. But the site I mentioned will steer you in the right direction.

John

Re: Onan 6.5nh propane conversion (3.00 / 0) (#3)
by Old F on Sat Sep 27th, 2008 at 06:52:15 PM MST
(User Info) http://www.oldf.homestead.com

Here is a conversion I did a few years back
http://www.fieldlines.com/story/2003/9/1/82526/70829

Old F

[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#12)
by bgarrett on Tue Oct 14th, 2008 at 01:38:27 PM MST
(User Info)

Dave Sipes, did you use earthtubes for cooling?
You had posts2 years ago
I want to do this and need info
thanks manyolkars at yahoo.com

[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#6)
by jgnat1488 (jgnatow at yahoo dot com) on Sun Sep 28th, 2008 at 05:24:41 AM MST
(User Info)

The first regulator is the one from the forklift. Not sure of the btu but i figured they matched it for the lift so it should handle my little engine just fine. On the same note i did see a bbq regulator at tractor supply that was 100k btu, that should be enought to run a good size genny.
Jason Gnatowsky KG4FJC Buckingham, Va. "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety. "
[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#4)
by dnix71 (yahoo.com 'dnix71') on Sat Sep 27th, 2008 at 11:27:46 PM MST
(User Info)

The carb has the governor on it so it loads correctly? I took an 2 cyl. 16 HP gasoline Onan genset that was rearended on a bus to Miami after hurricane Andrew in '92. I had to rig up a spring and wires to make it run okay under load because the intake manifold was broken when the bus backed over something.

My first attempt produced about 200 volts and smoked an electric chainsaw I plugged in.
The second attempt with the help of a Radio Shack multimeter got it running correctly with the pastor's refrigerator. They were "off-grid" the hard way for 45 days because all the utility poles were snapped by the storm, as was FPL's high voltage feed along US 27.

The pastor woke up from the storm with a transformer in his swimming pool. That Onan was so heavy it took four adult men to pick up and set down. They sure don't make things that well any more.

Re: Onan 6.5nh propane conversion (3.00 / 0) (#5)
by tanner0441 on Sun Sep 28th, 2008 at 03:26:35 AM MST
(User Info)

The question I have is if the demand unit is from a fork lift truck, is it a vapouriser. ie ment to be fed with liquid propane and water heated. If so it has both regulator stages. vapouriser, and first stage to around 100 psi, into the second stage which is a zero biased guvenor, no suction at the outlet, no flow.

Propane has 19,500 BTU per pound, so you can work out your requirement if you can borrow a gas analizer the stoichometric mixture is 14 - 17% and you can regulate the flow to the engine with a screw into the carb fitting.

Look at CAT forlifts they used a US made Beam system with lots of set up data.

Brian.

[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#7)
by jgnat1488 (jgnatow at yahoo dot com) on Sun Sep 28th, 2008 at 05:42:24 AM MST
(User Info)

Yes it is vaporrizor style regulator. It was hooked up to draw liquid. However I did some looking and most can run vapor just fine so long as the demand isnt too high. I run vapor threw out since i am only running at most 20HP, the regulator is rated for 85HP from liquid. It does shut off flow if no vacuum is "felt" kinda like a scuba regulator. The "mixer" sits just above the shaft for the choke and is how it senses vacuum. It only takes a very slight vacuum and it starts flow, too much and it shuts off flow allso. These regulators are really neat in how they work. I was worryied about getting the ratio correct so i installed a ball valve between the regulator and mixer, it turns out that the regulator does a real good job of that. The ball valve is fully open, if slightly closed the engine starts losing rpm. It handles 5000watt load fine so idont think i am too lean. Amount of fuel is controled by amount of vacuum so if the mixer was to be lower in the throat of the carb it should fuel richer, if raised it should lean out. I think i have it pritty close (accidently on purpose) :)
Jason Gnatowsky KG4FJC Buckingham, Va. "They that can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety. "
[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#8)
by tanner0441 on Sun Sep 28th, 2008 at 11:56:39 AM MST
(User Info)

The vapourizer style regulator will have no problems with vapour, the problem could come in the bottle where the liquid becomes a gas, if it can't get enough heat back into the bottle, you will get a frost line round the bottle at the liquid level. Propane boiles at minus 44 C, and expands around 700 volumes. At around 65C the tank pressure with no take off will be around 150PSI.

The carb adaptor can be a simple pipe entering the air flow anywhere above the narrow part of the choke tube, it is refered to as a spud adaptor, we used to drill through the side of the carb just below the air cleaner clamp. Some vapourizers have a solenoid on the second stage to give a gas purge to assist in cold starting. Air cooled engines had a vapourizer that was a concentric pipe that went into the exhaust.

There should be no problems with what you are trying to do and the engine life will be extended, propane is carbon deficient in its combustion so it will clean the engine, if you have trouble starting close the plug down 5 thou propane has a higher ignition temp, if the engine has points not electronic ignition it could eat the points more quickly, it has a slower flame front so there is a longer push on the piston so the bearings should last longer.

good luck

Brian

[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#9)
by RandomJoe on Sun Sep 28th, 2008 at 01:08:49 PM MST
(User Info)

There should be no problems with what you are trying to do and the engine life will be extended, propane is carbon deficient in its combustion so it will clean the engine, if you have trouble starting close the plug down 5 thou propane has a higher ignition temp, if the engine has points not electronic ignition it could eat the points more quickly, it has a slower flame front so there is a longer push on the piston so the bearings should last longer.

This reminds me of something that's been bugging me. I had always thought running a generator on propane or natural gas would make it live longer, but when I was looking at generators to purchase earlier this year, I kept finding comments on the various websites (mostly dealers' sites, don't remember if I saw any on a vendor's site) clearly stating the opposite - that a generator run on propane or natural gas would have to be replaced sooner. In some cases, considerably sooner!

So, why would they be saying that, when it seems fairly logical that it should live longer? Or maybe I missed something - I was lumping propane/NG together, but only paying attention to NG since that's what I would have run.

[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#10)
by tanner0441 on Sun Sep 28th, 2008 at 03:02:42 PM MST
(User Info)

If the engine has high carbon valve seats it can suffer damage to the seats, and rotory engines ie Wankel require fuel lubrication of the rotor tips, and suffer excessive wear of the tips.

As several generator companies offer LPG as an alternative fuel option, and CAT do an engine that will run on diesel, petrol, or various gasses by selecting the choice of fuel from the panel, but they are 12 ltr V12 not used in many RVs.

Generator manufacturers don't normaly go for high performance engines, 900, 1500, or 3000 depending on the number of poles, sorry in the US those RPM figures will be corespondingly higher. I would have no hesitation in running a small domestic generator on LPG, add to the fact the exhaust gasses are mainly CO2 and water, the Nox products are minimal.

Hope this helps

Brian.

[ Parent ]

Re: Onan 6.5nh propane conversion (3.00 / 0) (#11)
by Ungrounded Lightning Rod on Tue Sep 30th, 2008 at 07:26:29 PM MST
(User Info)

... [propane] has a slower flame front ...

Sounds like it might be a good idea to advance the spark a tad, too. More power and efficiency.

[ Parent ]

Onan 6.5nh propane conversion | 12 comments (12 topical, 0 editorial)

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