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Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan 4.0 BFA Project


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  #1  
Old 08-30-2017, 08:58:26 PM
Handyhiker1 Handyhiker1 is offline
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Default Onan 4.0 BFA Project

I picked up a new to me project tonight, a 4.0 BFA that is missing s few parts. It needs an intake manifold, carb snd air cleaner housing. It is a low hour unit, less then 100 according to the seller. One of his mechanics took it apart to paint it and got put in jail for DUI multiple times. He couldn't find where the parts were. It was going to be painted red. He also has a 1957 4.0cck that was in process of being painted and torn down. Also missing some parts.
I looked at the tag and it is stamped as a 1R but it does have the 4 leads out of the generator and the diagram under the cover does show 120/240 hook ups.
Billy has offered a manidold so now I need ro find a carb and air filter housung. Here are a few pics.

Here are the numbers.
4.0 BFA-1R716004A
D783335357
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  #2  
Old 08-30-2017, 09:49:32 PM
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Billy J Shafer Billy J Shafer is offline
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Default Re: Onan 4.0 BFA project

I have your manifold almost ready to ship. But with the water problems down here. A little slow. I also have the air filter assembly.
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Old 08-30-2017, 11:13:23 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 4.0 BFA project

Those 4.0 BFA's are tough. I tried to kill mine in many ways and failed. Human piss poured down the carb did absolutely nothing to it as well as anything else that I could find (no, I did not poop on it). I ended up giving up and restored it. Good luck with yours.

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Old 08-30-2017, 11:22:17 PM
yellowlister yellowlister is online now
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Default Re: Onan 4.0 BFA project

I think pooping on it would just make it stink, depending on where the poo landed might make it burn just make the neighborhood and you smell like poo...that is if it has the same effect of pissing in a fire..
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Old 08-31-2017, 04:48:11 AM
Handyhiker1 Handyhiker1 is offline
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Default Re: Onan 4.0 BFA project

Quote:
Originally Posted by Billy J Shafer View Post
I have your manifold almost ready to ship. But with the water problems down here. A little slow. I also have the air filter assembly.
No hurry. I am sure you have bigger things to worry about. If you have both pieces, I would really appreciate them. I got 2 new carbs in the parts I bought last weekend but sure enough, they are not for a BFA.
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Old 08-31-2017, 08:07:47 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Onan 4.0 BFA project

Well, good and bad news. I pulled all the output wire off this and just threw it away after finding that stuff on the 12.5 JC. After that I did turn it over with a socket and ratchet just to see how it felt. Almost no compression. Pulled the plugs,and both were almost completely carboned over. There was no gap, just carbon. With the plugs out I could look in the cylinders, yup, lots of carbon!!
I pulled the right head and could not believe all the crap in the cylinder. Below are before and after pics. Tomorrow I will tackle the other one.
I really do believe that this is a low hour unit but I believe it had a rough life. With that much in the cylinders there is no way it has ever been worked very hard. There was no lip in the cylinders and some of the cross hatch is still there. All in all, I think a good cleaning and going over then to find a carb and life will be good.
With the plugs out did hook up a battery charger with start boost and spun her over. The start switch works and after cleaning the plugs, there was spark. Only did it for a couple seconds just to check for spark and if it would turn over.
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Old 08-31-2017, 08:16:04 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 4.0 BFA project

How does the cylinder bores look? See any hone marks? Or smooth as a baby's azz? After cleaning it up and putting it back together, do a compression test. I think I have NEW head gaskets. They are made of composite graphite. I was able to reused my old (non composite) head gaskets. You may be able too, but it you determine that your head gaskets are toast, I will look for my gaskets and send you my new head gaskets FREE if you commit to getting the BFA running.

JohnnyC
New Jersey
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Old 08-31-2017, 08:32:12 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Onan 4.0 BFA project

There are home marks in the cylinder. There was some really light pitting on the botom but not nough to worry about. The head gasket looked good. I cleaned it up and it is already reinstalled. The BFA WILL run again. The carbs I have are for a BEG and from what I can figure out, a welder. Might sell them to get money to buy the right crab.
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Old 08-31-2017, 08:40:50 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 4.0 BFA project

Quote:
Originally Posted by Handyhiker1 View Post
There are home marks in the cylinder. There was some really light pitting on the botom but not nough to worry about. The head gasket looked good. I cleaned it up and it is already reinstalled. The BFA WILL run again. The carbs I have are for a BEG and from what I can figure out, a welder. Might sell them to get money to buy the right crab.
The original carburetor for my 4.0 BFA is a Walbro, but I was able to run a Niki carburetor from a larger T260G Onan motor without any problems. The Niki carburetor from the T260G motor has a much larger venturi than the OEM Niki on my 6.5 NH. I assume the larger venturi was for more air flow required for the T260G motor that was mounted on a zero turn lawn mower and the motor was designed for up to 3600 rpm use. The Niki and Walbro carburetors swapped without a single modification to the BFA's motor's manifold and linkage.

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  #10  
Old 08-31-2017, 09:09:51 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Onan 4.0 BFA project

The carb I have uses a rubber fuel hose and a manual choke. The part number is 146-0660.

Here is a guy selling a used one and wants $200. Mine is new in the box.

Look at this on eBay http://www.ebay.com/itm/171670219086
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Old 09-01-2017, 06:04:46 AM
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Default Re: Onan 4.0 BFA project

Looking for the carb that I need, 146-0419, I have found prices from $250 - $350. These old parts sure bring a high price! Oh well, the final outcome will be worth it.

Question on the choke assembly, any idea if there is a part number for the whole set up? I looked at the parts break down and it looks like each piece is separate. Guess I will be on a parts hunt.
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Old 09-01-2017, 09:45:25 AM
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Default Re: Onan 4.0 BFA project

I've got what you need pm me.
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Old 09-01-2017, 05:25:36 PM
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Default Re: Onan 4.0 BFA project

Pm sent.
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Old 09-01-2017, 07:27:45 PM
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Default Re: Onan 4.0 BFA project

Sicker then a dog tonight. I will pull the other head and clean it up tomorrow. Then tear into the generator and clean slip rings and chech things out. Going to wire in a couple outlets too so when I can it will be ready to test.
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Old 09-02-2017, 07:24:18 AM
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Default Re: Onan 4.0 BFA project

I know that I am not a smart guy when it comes to these machines but I really don't understand this. For spec A they use a 167-0237 spark plug, after that, they use a 167-0298 spark plug. All the ignition components seem to be the same from what I see on the parts break down. I tried doing a cross reference on the plugs but must be having a brain fart day today with this head cold I got. What is the difference in these plugs and what is a cross reference for them?
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Old 09-02-2017, 08:06:01 AM
KPack KPack is offline
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Default Re: Onan 4.0 BFA project

Anybody know if the spec c carb will fit the spec a unit ?

Last edited by KPack; 09-02-2017 at 08:30:06 AM.
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Old 09-02-2017, 08:33:21 AM
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Default Re: Onan 4.0 BFA project

Pictures of the carb.
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Old 09-02-2017, 10:48:25 AM
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Default Re: Onan 4.0 BFA Project

The parts diagram doesn't show a different part number or different adapter.

I tore the other head off and found a stuck open exhaust valve. Thought it was bent because it angles down but looks okay after freeing it up. Pulling the tappet cover there I'd a lot of sludge in the motor. I don't know if they ever got it really warm and worked it good or just short runs. After I get it running will have to do a good oil system flush and a few bottles of intake/carb cleaner. Even the intake valve stems are covered in sludge.
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Old 09-02-2017, 10:52:33 AM
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Default Re: Onan 4.0 BFA Project

Here is the second cylinder. The good news is you can still see the cross hatch.
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  #20  
Old 09-02-2017, 11:12:06 AM
Kevin K Kevin K is offline
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Default Re: Onan 4.0 BFA Project

As long as you have the heads pulled, you might as well remove the valves and give them, and the intake and exhaust ports, a good cleaning. It is something I always do.
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