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Onan Generators

Onan 12 MDJC - 3r/2268d (1985)


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  #61  
Old 08-10-2017, 10:24:57 AM
PnishrPW PnishrPW is offline
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Voltage regulator (Magnicitor). If the gen is run at lower than normal rpm the coils can smoke. Unfortunately, they are almost Unobtainium...
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  #62  
Old 08-10-2017, 11:43:05 AM
sscummins sscummins is offline
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

PnishrPW,

How do I disconnect the Voltage regulator?
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  #63  
Old 08-10-2017, 01:18:10 PM
PnishrPW PnishrPW is offline
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Not super familiar w/ the Magnicitor sets, hopefully Leon will chime in - he's the resident guru on those. Shouldn't be too hard, just a couple of wires to tag/disconnect.
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  #64  
Old 08-10-2017, 05:02:01 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Leon,

Can you please advise what needs to br done for disconnecting a Voltage regulator on my 12 MDJC-3R/2668D. In a nut shell I am in the process of getting an old lady running and dont want to burn anything up if she is slow at RPM,

Many thanks in advance.

Steve
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  #65  
Old 08-10-2017, 09:00:06 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Steve to disconnect the magneciter remove the E1 and E2 connections from the terminal strip on the gen head. This isolates any power from reaching the magneciter which in turn stops any from going to the field. The issue with the magneciter is that if the generator is run at a reduced speed for any length of time the magneciter coils can overheat and be damaged. The coils of your magneciter appear to be a nice golden color which means they are probably in good shape, if they were dark brown that would be a warning sign. The whole problem with this is that we have never heard a reference quoted of how long it takes to damage the coils or what engine speed is too slow. In order to determine engine speed either the magneciter needs to be hooked up and a "Killawat" meter or a good multimeter like a Fluke with a HZ range used, Or alternately a mechanical or optical tachometer used. So you are going to need one or the other of these devices, the Killawat is the cheapest around $25 and is a handy thing to have when working on generators.
My personal opinion based on working with magneciter equipped Onans is that running for a few minutes at a reduced speed is unlikely to to damage the magenciter coils, I wouldn't think more than 5 mins would be required to establish and adjust the engine speed to within an acceptable range around 1800 rpm or 60Hz. I hope this helps clarify a bit. Cheers Dan
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Old 08-11-2017, 02:41:22 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Dan,

thank you, yes it makes sense and wont want to take any chances or risks. I want to keep this deal as best as it can be without any help making it worse from myself. I plan on getting this running and checking RPM making sure Iam at 1800 rpm. What would be a good + or- for closeness to 1800rpm? I have access to a good digital tachometer. Hoping to get time either this evening and meeting PnishrPW or saturday for the rectifier. thats the only piece of the puzzle that is known to complete it and start her up. Oh I need to attach a small fuel tank. I dont want to hold a 6'x1'x1' tank off of the trailer this came off of. LOL rather use an old lawn mower tank just to get some black smoke out. FEELING anxious guys. like a kid in a candy store.

Thanks again,
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  #67  
Old 08-11-2017, 07:02:11 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

I would say +- 50 rpm would be safe and maybe a bit more since this is the approximate range from loaded to unloaded Hz. Cheers Dan
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Old 08-13-2017, 05:03:02 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Well everyone, i had a starting issue and thanks to Dan pinshrpw, i was able to locate problem, the new diode and plate i got from him that i installed turned due to lack of access to removal of other bolt from old plate cause new plate to ground out to start taggo swithc cause a starter activate when nattery hook up, scared the crap %$#$%^*, but 20 min later found and moved, 5 minutes later she was sputting firing and started, ran her for 5 minutes toll most of the blue, white black smoke went away and rinning smoother, will check later this week on rpm and colling fan hookup, anti freeze and all important stuff, work in progress everyone, and the knowledge and help from all of yoy shows me that it happened with all your help, AND I THANK YOU ALL VERY VERY MUCH!!!!!!! More to cum later when i get her home fixed up where this 12kw will be resting until shes fired up.��
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  #69  
Old 08-14-2017, 11:38:47 AM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Glad you got it going, happy to help!
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Old 09-06-2017, 03:19:48 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

I am back and found that I have 2 cylinders leaking water and whiting out my exhast, turns out the gaskets blew and am checking to see if heads are worped or not, Do you and anyone knopw a less expensive place to buy head gaskets #110-2944. I believe felpro made them for onan? I cant see spending $156 FOR ONE AND i NEED 2? OUCH!!!!

Anyone out here to help?

Thank you
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  #71  
Old 09-06-2017, 04:19:04 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

You could check here, they are a sponsor on this sight:

www.gasketstogo.com
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  #72  
Old 09-06-2017, 04:44:01 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Unlikely the heads warped they are a big chunk of cast iron not aluminium. Also being two separate heads then can move a bit. Cheers Dan
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Old 09-06-2017, 07:19:58 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

What do you mean dan that they are 2 seperate heads and they can move? Please adbise i dont understand this, thanks again steve
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  #74  
Old 09-06-2017, 08:11:21 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

They can move relative to each other.
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  #75  
Old 09-06-2017, 10:13:49 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

The MDJC has 2 separate heads each serving 2 cylinders, they are functionally identical to each other and also to the single head on an MDJE/B. The fact that they are separate means that there is less chance of misalignment than if there was one long head covering all four cylinders. Cheers Dan
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  #76  
Old 09-07-2017, 08:24:59 AM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

Thanks Dan,

Does anyone else know where I might find the head gaskets, I found a place in Pennsylvania I think that is out of stock and priced at $59. Cummins northwest can get them for $155 each, wow big difference,.

Any suggestions are much appreciated.

Thanks to all
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  #77  
Old 09-07-2017, 01:30:19 PM
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Default Re: Onan 12 MDJC - 3r/2268d (1985)

As noted in an earlier thread, "Gaskets to Go" is a good place to get them. Takes 2-4 weeks, however. Go to their web site - Gasketstogo.com. I recently bought a couple for my 6MDJB. Sent them all the drawings, etc. They fit nicely. And, about 59.00 each. zuhnc
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