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Onan Generators

Onan 7.5JB-3CR/9804T - Welcome 'red' to the family


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  #11  
Old 03-04-2016, 11:41:41 PM
BStrutton BStrutton is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Well it begins..

The semi pulled up to the house yesterday unannounced and delivered the JB. Here's the state of affairs for those that were curious about this one..

Nest and 2-3 chewed wires in the control box that i can see so far. If hobbs is to be trusted it says 875 hours. Oil has pretty strong fuel smell.

On my NH theres an access panel for the gen end. Im not seeing it on the JB. Wanna take a look for other wiring damage. Fingers crossed. Theres a sheet metal piece with 1 wire attached that looks like part of the metal corroded away. Pic attached. What is this piece?

Never dealt with mice.. Thinking to check gen end and if ok will fix the few CBox wires, change the oil / filter / fuel and see if itll fire after checking proper ground as instructed.

Anything else?

Thanks!
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  #12  
Old 03-04-2016, 11:46:48 PM
Dale Russell Dale Russell is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

If it has Fuel in the Crankcase, I think I would look into putting an Electric Fuel Pump on it just to be safe Good find!
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  #13  
Old 03-04-2016, 11:52:21 PM
nothingbutdarts nothingbutdarts is online now
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

I would pull the back cover off the gen. end and look for mice damage in there before trying to start it. Also make sure it's grounded as per what Leon N. posted. The magnaciter generator section DOES NOT LIKE to run below 1,800 RPM or it can make the magic smoke that is expensive to repair!!!
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Old 03-05-2016, 12:31:53 AM
Ray Lynch Ray Lynch is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

There should be a metal cover over the area where the ignition coil is located. Do not run the set without this cover installed or the set will overheat.
I would clean all wire connections and terminals before attempting to start. Looks like gasoline in the glass bowl. May want to inspect and clean carb.
I can look at my set in the am to see what the metal/ground piece might be if nobody else identifies it beforehand.
Thanks for posting.
Ray
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Old 03-05-2016, 05:58:39 AM
BStrutton BStrutton is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

More fun.. And yes, i do know I shouldn't be lying on the garage floor at 4am Just couldn't stand the suspense..

https://youtu.be/vVf70_5hhMc
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Old 03-05-2016, 08:23:08 AM
terry smith terry smith is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

I had seen that listed for quite a while and thought that the price was pretty fair. You got a very good deal. I think with just the housing alone you got your moneys worth. Look for a decal on it from Defelice construction, they owned it last and used on a jobsite, That is where it got its red makeover.


Great Find
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Old 03-05-2016, 08:51:23 AM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

The piece of aluminum with the rectifier in it (rotted piece of metal) is the heat sink. Reattach it or make a new one, not a big problem. Some of the relays may be a different story.

Remove each screw in the terminal strips & clean the connection, half of the heads will likely break off. Usually the rest of the screw will come out easily. The mouse urine is very hard on the brass screws.
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Old 03-05-2016, 09:09:59 AM
Leon N. Leon N. is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Bstrutton, wow! You have a diamond in the rough! First off, do not be in a hurry to start this JB. From your pictures, looks like your magneciter is OK, that is it does not show signs of over heating which can happen from of all things like running the JB below 1800 RPM. Mice got into my control box also. See my picture after I cleaned it up. Still have a couple of insulation chewed wires, but have not got around to replace them.

If I were you I would go over the magneciter first by cleaning out all that mice crap. DO NOT LOOSEN ANY WIRE CONNECTIONS AT THIS TIME. Just look for broken wires or any bare wires that may touch the frame and cause a short. If so, maybe just tape them up for now.

In your control box do the same. If the relay contacts that are exposed and appear dirty, try some contact cleaner first. No problem replacing chewed wires in the control box. These circuits operate at 12 VDC. But for the back end exciter, I would not disconnect anything. I think you will luck out and it will be OK. Just blow out all that crap.

Find the neutral T2 from the generator and make sure it is tied to the chassis before even thinking of starting it. You may have a bad fuel pump which caused gasoline to get into the CC. Maybe not. I would stay with the original fuel pump if you can determine it is OK. You can R & R the fuel pump very easily. When you get ready to crank, make sure you changed the oil and note cranking oil pressure. It should come up while cranking. If not STOP and find out why.

More later. Got to make breakfast now.
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  #19  
Old 03-07-2016, 03:25:56 AM
BStrutton BStrutton is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

After the fiasco that was trying to unload the JB off the pallet onto my lift cart with an engine hoist (too narrow to straddle the pallet), I spent some time cleaning out the worst of the mouse stuff from Cbox & genend.

I found what appears to be a single ball bearing & am wondering where that came from. Rotor bearing (# 6 in the parts manual) came to mind but it looks sealed & unlikely to cough up a ball in the diagram??

Mystery bearing: https://www.dropbox.com/sc/fse7kiscz...U4O5pmz6umbXha

Also it looks like some mouse nest further back in the gen end than the end cover allows me to access. I'm wondering if I should disassemble the genend, though I don't really want to. How painful is it to take apart. As a point of reference I've torn down a couple of 6.5NHs soup to nuts..

Finally, where are you guys getting good wire and connectors for the control box work? Most of the stuff I see these days anywhere local feels pretty junky..

Thanks.
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Old 03-07-2016, 09:07:04 AM
terry smith terry smith is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Head to your local electrical supply house and order a roll of a roll of 18 gauge MTW wire. MTW is Machine Tool Wire and is quite flexible due to its higher strand count and will tolerate vibration quite well. You can find braided sleeve loom at any good industrial supply house like Grainger and build you own harness.

Good Luck, Terry
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