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Onan Generators

Quick help with Onan 12.5


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  #81  
Old 04-08-2017, 07:11:08 PM
Leon N. Leon N. is online now
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Default Re: Quick help with Onan 12.5

Re post 75 in regard to the governor spring. From my experience and knowledge and reading the Onan documents, unless you are very very lucky, you MUST use the Onan specified governor spring or you will never get the 5% droop performance. Using what may look like a similar spring is going to be very frustrating. No way that spring can come disconnected if installed properly.
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  #82  
Old 04-08-2017, 07:31:52 PM
len k len k is offline
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Default Re: Quick help with Onan 12.5

Stiffness of a spring is proportional to the 4-th power of wire diameter. So a little rusting can change spring constant ( #/inch) a lot. Haven't analyzed it, but I'ld guess the "lever arm" adjustment (up and down one) can compensate for that, as long as spring was close enough.
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  #83  
Old 04-08-2017, 07:53:40 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

The one spring did have some Onan green paint. I assume it was the factory spring. The one threaded rod was square and fits in the hole and won't turn. Not sure how they fell out but I think they are the factory ones.
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  #84  
Old 04-08-2017, 08:17:24 PM
Max Thompson Max Thompson is online now
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Default Re: Quick help with Onan 12.5

Setting timing is covered in detail in the service manual. I pull the #1 plug and using a screw driver as mentioned previously (and also noted in the manual), insert the screw driver into the cylinder and rotate the flywheel until the piston is at its highest point. You should find the TC mark on the flywheel very close to the pointer. I used a 12-V test light as described in the manual (and still do) before I purchased a timing light.

It is very easy to get the distributor off by one tooth when installing it.
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  #85  
Old 04-08-2017, 08:32:13 PM
len k len k is offline
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Default Re: Quick help with Onan 12.5

When I got my JB spec aa , the hook end of the spring was broken off. I just made remaining into a new hook temporarily.
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  #86  
Old 04-09-2017, 07:46:29 AM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

Quote:
Originally Posted by Max Thompson View Post
Setting timing is covered in detail in the service manual. I pull the #1 plug and using a screw driver as mentioned previously (and also noted in the manual), insert the screw driver into the cylinder and rotate the flywheel until the piston is at its highest point. You should find the TC mark on the flywheel very close to the pointer. I used a 12-V test light as described in the manual (and still do) before I purchased a timing light.

It is very easy to get the distributor off by one tooth when installing it.
Max,
I did see that in the manual but figured that a running set would be more accurate. I am going to have to try that way and see what happens. If this distributor is off a tooth or two or whatever is going on, I can't believe how good this thing runs now and thinking that there is no way the distributor is off, but we will see.

Leon,
once I get this timing figured out I will work on a way to load this set as much as I can and check droop of the governor. Then I will have to figure out how to adjust the sensitivity of the governor. One thing at a time though.

One comment, I said early on in this thread that I had no experience with this unit or anything this large. I sure do now and getting more every day. The one thing you can say about working on old Onans, it seems to never get boring. I know that I am not that smart when it comes to these but there are sure some top notch folks on this site, thanks for the education and the patience.
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  #87  
Old 04-13-2017, 05:56:00 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

Okay, latest update. I was able to set the timing with the engine NOT running. To my surprise, my by the ear timing was actually really close. I also got the valves adjusted and then when running, adjusted the governor. But of coarse with success comes defeat. When pulling the valve covers, I broke the rear lifting arm mounting bolt. The front one came out nice and easy, the back wouldn't budge. I took a couple of pics of the top end of the engine, I could not believe how clean it was inside. So for now running wise, it is all set. Now to clean it up, change the oil again and make the new exhaust flange, oh ya, and drill out the lifting bolt.
I also have one more question, there is a hole in the control box in the same location as the start/stop switch but on the other (front end) side of the cover. I have no loose wires in the control box, what was supposed to be here? I will post a pic in just a little bit.
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  #88  
Old 04-13-2017, 06:16:31 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

Here are the pics of the engine top end and the mystery hole.
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  #89  
Old 04-13-2017, 07:37:42 PM
Ben Clarke Ben Clarke is offline
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Default Re: Quick help with Onan 12.5

Entrance to mouse hotel???
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  #90  
Old 04-13-2017, 08:20:36 PM
Leon N. Leon N. is online now
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Default Re: Quick help with Onan 12.5

On my JB that is where the Hand Crank/Electric Start switch is mounted.
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  #91  
Old 04-14-2017, 07:21:26 AM
Max Thompson Max Thompson is online now
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Default Re: Quick help with Onan 12.5

It may have had a button plug in that hole from the factory.
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  #92  
Old 04-14-2017, 11:35:54 AM
suntreemcanic suntreemcanic is offline
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Default Re: Quick help with Onan 12.5

Mv JC manufactured in '82 has a button plug in that in that hole.
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  #93  
Old 04-14-2017, 01:16:52 PM
Jack Hottel Jack Hottel is offline
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Default Re: Quick help with Onan 12.5

So did my 84 JC, until I mounted a switch there to isolate the transfer switch control lines when I wanted to start the unit locally.
Jack Hottel
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  #94  
Old 04-14-2017, 01:55:01 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

I assumed it was nothing major as there are no lables there, just wanted to check. Thanks all.
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  #95  
Old 04-14-2017, 02:01:26 PM
Leon N. Leon N. is online now
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Default Re: Quick help with Onan 12.5

Handyhiker1 WRT your post #88, make sure the oil lines in the valve cover that spray cooling oil on the valves and lubricates the valve guides is clear and not plugged. That also goes for the external oil line that feed oil to this area. Very important.
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  #96  
Old 04-14-2017, 03:41:11 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

Quote:
Originally Posted by Leon N. View Post
Handyhiker1 WRT your post #88, make sure the oil lines in the valve cover that spray cooling oil on the valves and lubricates the valve guides is clear and not plugged. That also goes for the external oil line that feed oil to this area. Very important.
I did take a wire and poke it in the holes and then sprayed some carb cleaner in and the lines were clear. Everything I could see in the top end looked great. I saw no dirt or grime of any kind.
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  #97  
Old 04-14-2017, 04:07:54 PM
Leon N. Leon N. is online now
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Default Re: Quick help with Onan 12.5

Yes that is a good idea. Now since you are working with a JC, be aware that the external oil line (pipe) that runs from behind/above the oil filter up to the cylinder heads has, I believe a flow control orifice at the ends where they screw into the valve covers. Make sure these pipes and orifices are clear as well.
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  #98  
Old 04-14-2017, 06:59:56 PM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

Okay thanks, i will check them out.
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  #99  
Old 04-15-2017, 10:14:48 AM
Handyhiker1 Handyhiker1 is offline
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Default Re: Quick help with Onan 12.5

I looked in the manual but did not see a spec for natural gas consumption for my JC. Can someone please tell me the flow rate I need to alloy for full output? I want to make sure my piping and hose will allow enough flow. Also as of now, witch may change, I would like to be able to use a quick disconnect for the gas line and need to know what size quick disconnect I would need.
Thanks
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  #100  
Old 04-15-2017, 10:53:08 AM
Max Thompson Max Thompson is online now
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Default Re: Quick help with Onan 12.5

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Originally Posted by Handyhiker1 View Post
I looked in the manual but did not see a spec for natural gas consumption for my JC. Thanks
That info is in #T-015 gaseous fuels manual. I think it is on the twainslan site.
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