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Generators In this forum we will try to answer any of your questions about the different model generators that can be found on Blue Bird coach's.

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  #1  
Old 12-20-2019
hifreqdude hifreqdude is offline
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Exclamation Onan 12.5 JC3 CR issues Y end unit.

Okay, kind of stumped at the moment,

I assembled a new voltage regulator using a SX460 and 8ohm resistor after much research to try and get it right the first time.
Put it together, made sure the disconnect was off and no load, fired it up and the genny leveled out in about 5-7 seconds. The Amp-meter went to 5 and seemed fine for about 40 seconds, and I was about to get happy.


Sitting right in front of the unit, I was just about to get up and go engage the disconnect, when a distinct sound came from the stator housing like someone tapped on the end of the shaft mildly with a ball pined hammer.
The voltage fanned back down to nothing again.

The engine never missed a lick.

I am hoping not to have to drop it yet if I do not have to.

I did get the end cover off and tested the diodes, which seemed fine prior to assembling the new regulator and running the unit.
Anyone ever have this issue, or an idea?
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1978 FC 35
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  #2  
Old 01-01-2020
hifreqdude hifreqdude is offline
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Never Mind, I will be dropping the unit out tomorrow to tear into it.
Just thought someone might have had some input. No worries.
Please disregard initial request.
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1978 FC 35
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  #3  
Old 01-02-2020
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Randy Dupree Randy Dupree is offline
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I don't think any of us have any knowledge about that Onan.
There was not many onans put in Birds,and i still don't know what Onan that is,the model number does nothing for me.
Pics may help.
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2000 LXI 43
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  #4  
Old 01-02-2020
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Bill Pape Bill Pape is online now
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Quote:
Originally Posted by hifreqdude View Post
Okay, kind of stumped at the moment,

I assembled a new voltage regulator using a SX460 and 8ohm resistor after much research to try and get it right the first time.
Put it together, made sure the disconnect was off and no load, fired it up and the genny leveled out in about 5-7 seconds. The Amp-meter went to 5 and seemed fine for about 40 seconds, and I was about to get happy.


Sitting right in front of the unit, I was just about to get up and go engage the disconnect, when a distinct sound came from the stator housing like someone tapped on the end of the shaft mildly with a ball pined hammer.
The voltage fanned back down to nothing again.

The engine never missed a lick.

I am hoping not to have to drop it yet if I do not have to.

I did get the end cover off and tested the diodes, which seemed fine prior to assembling the new regulator and running the unit.
Anyone ever have this issue, or an idea?
My guess is the hammer noise is not normal, seems it needs to be taken apart. This Onan may not be an original from BB, the only place to find information on your Onan is in the generator site, smokstak

https://www.smokstak.com/forum/threa...ssible.144052/
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  #5  
Old 01-02-2020
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I saw a big 12.5K air cooled Onan in Cheddar Yeti back in 2012, that's all I've got on it
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  #6  
Old 01-02-2020
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Randy Dupree Randy Dupree is offline
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Ahh,after looking at the pics i remember having one of those Onans.
It was a propane version and i ran my 3 phase equipment with it at my florida shop.
All we ever did was change the oil in it,i bought it at auction at a grocery store,it was the backup genny for the office.
The military had those gennys in diesel configuration,but 24volt dc for starting.
Aircooled.
Kinda of a cool engine,available in 2 cylinder and 4 cylinder.
Of course none of that trivia helps you fix it.
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  #7  
Old 01-02-2020
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I had one of those in my 78FC. I had a hard time keeping it going, points, choke, etc. I eventually replaced it with a generac 7.5 quiet box. That is a very big and heavy generator.
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  #8  
Old 01-03-2020
hifreqdude hifreqdude is offline
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Thanks for the replies, it is original to the bus as I bought it from the first owner and the connections have never been altered from what I have been able to determine.
It is heavy, but it works the ac’s Very well so if I can fix it I will.
I have the service manuals now and will go through it. If I can get bearings, gaskets and rings I will go ahead and freshen it up after fixing the output.
A diesel would be nice, but only have room for air cooled unit, and we are looking at getting a bigger coach so we can get a queen bed in the rear and a shower that don’t need a shoe horn to get into. It is a great bus, but we have used it enough to determine it will not suit our long term goals.
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  #9  
Old 01-05-2020
Tim876 Tim876 is offline
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Joe, I have the same unit...a "JC" series air cooled Onan, which was original to my '78 as well. They were a very popular stationary backup unit in their day. Popular enough in fact that Cummins/Onan still stocks almost all of the parts for them (from carb rebuild kits, tune up parts, seals, etc.). I've rebuilt the carb on mine, and installed an electric ** l pump. It runs like a dream, and makes loads of power. The "old guys" at Cummins told me they used to load test the 12.5 kw JC units well beyond 15kw and they would just keep going. Only drawback I've com across if the noise and the vibration. I actually purchased a diesel Onan last week to replace my JC, really only to quiet things down and to not be stuck having the short run time (30 hrs ish) of the small gas tank. I do plan to conv rt my JC to natural gas and use it at my house as a backup generator. Lik I said, once tuned up they are extremely reliable!
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1969 Trojan SeaVoyager
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  #10  
Old 01-06-2020
hifreqdude hifreqdude is offline
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Hi Tim, I agree, it is a great unit. This thing runs two 15K units and anything else we wanted without even flinching. We have three new ac's but have not tried all at once, though I believe if need be it would handle the load. Running two on high will have you looking for a jacket.



We will not replace it. Primarily because we do plan on getting a bigger bus sometime in the near future and the cost would not be reasonably recouped, and those funds could be going to the new coach.(we have dropped a bunch of mullah in this bus already.) No regrets though, someone will get a well loved bus when we put it up.



If we were planning to keep this coach I would move to the diesel unit and do as you are, also I would add an auxiliary line from the main tank with a pump to refill the small tank on long outings. I may still make a slide tray for it, though I am on the fence about it, would be nice or someone else in the future.

I see that Onan Cummings has quite a bit of parts and they are proud of them also, but at least they can be gotten!

I already pulled and diagnosed the issues and plan to go through it.
Thanks for the info!
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