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Onan 12.5JC-3CR, Questions, Just purchased


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  #21  
Old 03-19-2017, 09:50:00 PM
Leon N. Leon N. is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

Hello again. A point of order, please. It looks like Onan back in 1973 when this JC was built took license to make changes to not only the amount of data put on this name plate as shown in this thread but also on the amount of information in not only the factory build sheet as shown in this thread but also in the wiring diagram, 612 C 2658.

For example, no Magneciter info on the nameplate, no mention if this JC has a low oil pressure cutoff, no evidence on ---6258 of a hand crank switch. However, from the picture in this thread, it looks like there is a hand crank switch on the control panel.

Also, the Onan JB/JC manual, 967-500 was printed well before 1973, probably in the early 1960's. The wiring diagram, 612 C 2658 appears on page 87 in 967-500 and it is dated 1955! Where as the one Max provided in post #2 is dated much later, like 1966 and does not show a hand crank switch. Onan does not reference the original --- 2658 in the post 2 version.

Guess what I conclude is one has to be very carefull to make sure the appropriate and accurate information is sourced for all this now old equipment as folks try to figure out what they have.

I feel fortunate in my case that Onan was still in business back in 1970 and I was able to obtain accurate descriptive documentation on my specific JB which was manufactured in 1966
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  #22  
Old 03-19-2017, 10:17:21 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

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Originally Posted by oakyone View Post
--- snip ---

Okay, now I see there is provision for hand cranking. I suppose that could come in handy if you didn't have a way to jump it, or the starter went gunny-bag when you needed emergency power. Now I'll have to shop for a J series hand crank!
If you get the JC setup for a hand crank, you MUST do a youtube video starting the JC with a hand crank and post a link here. I don't recall anyone every trying to do it or have done it, but I am new here with only 2 years or so experience with a 15.0JC and an 15RJC which I don't think I'd want to hand crank. It may be a first to see for many of us. It would be great entertainment. Oh, I hope your JC does not have high compression pistons

JohnnyC
New Jersey
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  #23  
Old 03-19-2017, 10:44:21 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

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Originally Posted by oakyone View Post
I'm going to have to try and get to the bottom of this propane solenoid. It's not shutting the fuel off, if that was it's purpose.
If you are talking about the fourth picture down in your first post on this thread, that center solenoid between the demand regulator and the pressure regulator, YES, that is the propane shut off/safety solenoid. It should energize/open when 12 volts is applies and close when no voltage is present!
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  #24  
Old 03-19-2017, 11:32:34 PM
oakyone oakyone is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

High Temp Switch.pdf

This is a page from parts manual 967-0220

It shows different high temperature switches for different configurations.

My set has the optional air shutters. Does anyone know the right temperature switch to use for mounting on the air shutters? There has been some disagreement on this topic. It seems like the one that mounts right to the exhaust manifold is set for 375°F. Seems like on a shutter model they would have mounted it to the shutters, but manifold would work as well. Just need to have much LOWER temp switch if it mounts on the shutters.

Thanks.
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  #25  
Old 03-19-2017, 11:45:49 PM
oakyone oakyone is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

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Originally Posted by JohnnyC View Post
If you get the JC setup for a hand crank, you MUST do a youtube video starting the JC with a hand crank and post a link here. I don't recall anyone every trying to do it or have done it, but I am new here with only 2 years or so experience with a 15.0JC and an 15RJC which I don't think I'd want to hand crank. It may be a first to see for many of us. It would be great entertainment. Oh, I hope your JC does not have high compression pistons

JohnnyC
New Jersey
I don't think I'd want to hand crank it either. We had old tractors growing up and the hand crank was always a LAST resort.
Shopping for the hand crank was a dry joke that didn't translate well in print!

I think I'll skip the fuel solenoid for now. I'll turn the propane off/on manually. If I ever set it up for an automatic transfer switch I'd need it. The thing must be really shot, because the generator is getting plenty of fuel WITHOUT the valve energized!
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  #26  
Old 03-20-2017, 01:15:36 AM
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BigBlockChev BigBlockChev is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

If you remove the solenoid from the piping and take off the screws on the bottom of the valve and remove the cover carefully you may be able to free up the rubber valve disc and get it to seal properly. They do stick from lack of use over time. Sometimes you have to remove the top as well to free it up too. Costs nothing , worked for me. Test the solenoid by putting 12V to it to see it move. Blow into the inlet while you have it off to check the sealing. Cheers Dan
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Old 03-21-2017, 01:07:13 PM
Mac Sine Mac Sine is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

Be certain that the demand regulator (the Garretson KN; the one closest to the carburetor) is "locking-off" when the engine is not running, even if gas is coming through the solenoid valve to the demand regulator. The demand regulator must not allow fuel to flow to the carburetor when the engine is not running.

The demand regulator is acted upon by carburetor venturi vacuum; this vacuum signal "pulls-open" the regulator and the fuel gas flows to the carburetor at sub-atmospheric pressure. The regulator should be set to crack-open at negative 1/4 to 1/2 inches water column (vacuum; not positive pressure).

Ideally, the fuel gas shut-off solenoid will be upstream of the primary regulator. Check the working pressure rating on the solenoid to determine if it can be moved upstream of the primary regulator. It may be a "low pressure" solenoid, if that genset was originally installed using natural gas fuel.
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  #28  
Old Yesterday, 12:45:05 AM
oakyone oakyone is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

She has new, NGK plugs (gaped at .035) cap, and rotor now. I had already installed the Pertronix ignition. The old cap had aluminum contacts - I paid a little extra to get brass. She's running very smooth now!

I'd like to have new plug wires handy, but having trouble finding a set (even a universal set) with the right angle plug going into the spark plug. Seems like the ones that come straight off the top of plugs would get bent down too much by the top air shroud.

Think i figured out the ignition system! The ignition is off until you actuate one of the start switches, OR switch "on" the hand crank switch. When the ignition is on the fuel solenoid IS energized (I was mistaken.) The centrifugal switch closes (I think at about 900 rpm) and holds the ignition on until the ignition is interrupted by a stop switch, low oil switch, etc. (The stop switch will cut the ignition even if hand crank is selected.) Does that sound about right?
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  #29  
Old Yesterday, 05:55:54 AM
JohnnyC JohnnyC is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

Regarding the plug wires, I had the same issue as you did when I restored a 15.0 JC. I made my own set of wires to resolve the problem. Not hard to do if you have the kits sold by Summit or Jegs (check online) and the outcome will be better.

JohnnyC
New Jersey
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  #30  
Old Yesterday, 07:03:26 AM
Max Thompson Max Thompson is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

Quote:
Originally Posted by oakyone View Post
Does that sound about right?
Yes, that is pretty close.

Glad to hear it is running well, now on to tweaking the carb and governor. Have you got a meter that will read frequency (Hz.)? A $20 Kill-A-Watt meter is handy for this process, plug it in and you have both hands free to do other things.
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  #31  
Old Yesterday, 10:17:20 AM
Leon N. Leon N. is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

Mr. Oakyone:

Re you comments and questions in your post # 28.

First off, I have remaining 4 ignition wires and the distributor lead which are high quality solid core wire and right angle boots for the plug end if you want them. I had to purchase the set which was designed for high performance 8 cylinder engines. I used two and gave two to another JB Stak member so I have four left, including the distributor lead. I believe they are plenty long enough for the JC. You can have them just send me a PM with your mailing address.

WRT to your other question in post 28, about that "hand-crank/electric start" switch. If wired correctly it will not shut off the machine in either position. The real start/stop switch will stop the plant if held in the stop position until the centrifugal switch opens. If the hand-crank switch is in the hand crank position the start/stop switch must be held in the stop position until the plant comes to a complete stop.

Leon
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  #32  
Old Yesterday, 12:04:48 PM
oakyone oakyone is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

Quote:
Originally Posted by Max Thompson View Post
Yes, that is pretty close.

Glad to hear it is running well, now on to tweaking the carb and governor. Have you got a meter that will read frequency (Hz.)? A $20 Kill-A-Watt meter is handy for this process, plug it in and you have both hands free to do other things.
I have a multi-meter with hertz function. One of the first things I checked - a I recall it was 61 or 61.5 with no load. I have a hertz gauge and two ammeter gauges on the way. I'm going to mount them somewhere on the set, so I can make sure both legs are somewhat balanced and keep an eye on the frequency. Thanks for the input.

Quote:
Originally Posted by Leon N. View Post
Mr. Oakyone:

Re you comments and questions in your post # 28.

First off, I have remaining 4 ignition wires and the distributor lead which are high quality solid core wire and right angle boots for the plug end if you want them. I had to purchase the set which was designed for high performance 8 cylinder engines. I used two and gave two to another JB Stak member so I have four left, including the distributor lead. I believe they are plenty long enough for the JC. You can have them just send me a PM with your mailing address.

WRT to your other question in post 28, about that "hand-crank/electric start" switch. If wired correctly it will not shut off the machine in either position. The real start/stop switch will stop the plant if held in the stop position until the centrifugal switch opens. If the hand-crank switch is in the hand crank position the start/stop switch must be held in the stop position until the plant comes to a complete stop.

Leon
I think you are right about having to hold the stop switch until it comes to a complete stop when it's set to hand crank. I believe mine is working that way. I've been holding it until it's completely stopped regardless.

I'll be sending you a message about those wires. Thank you very much. I'd like to include something for your trouble. Cheers.
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  #33  
Old Yesterday, 04:55:51 PM
Leon N. Leon N. is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

OK. I will get those wires off to you with my compliments in the next couple of days. Leon
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  #34  
Old Yesterday, 11:34:35 PM
oakyone oakyone is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

I've already repaired a rusted out section on the housing floor caused by a leaking batter who knows how many years ago. Right now, the whole housing is removed, except for the floor. The only thing holding the set on is the four rubber mounts.

Is there a safe way to lift the set off of the floor plate? I want to give the floor (and rest of the housing) a paint job to prevent future corrosion. I noticed the valve covers have threaded sockets in the top, but I'm VERY hesitant to lift the entire weight (engine and gen head) with those aluminum valve covers.
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  #35  
Old Today, 12:44:43 AM
suntreemcanic suntreemcanic is offline
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Default Re: Onan 12.5JC-3CR, Questions, Just purchased

Hello Oakyone, I live in Sisters. There is a angle iron that bolts to the holes in the valve cover that you lift it with. You can make it very easy. I have pictures of mine. If you would like to see it.
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