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Onan Generators

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


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  #1  
Old 02-28-2016, 05:41:21 AM
BStrutton BStrutton is offline
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Default Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Oops: http://www.ebay.com/itm/ONAN-7-5-JB-...YAAOSwMmBVySvx

With 2 6.5 NH spec K's already taking up space I didn't really need this but I couldn't pass on the doghouse and thought maybe I'd place this permanently instead of rolling out the 'portable' NH.. My blasting thumb is already starting to itch as I look at that crappy red paint on the doghouse.

Bit of a gamble for sure. We shall see. Wish me luck.

Appreciate manuals & any insight on what if anything the 9804T signifies? Serial is 0970257381. Year?

Thanks!
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Old 02-28-2016, 06:53:01 AM
Viking66 Viking66 is offline
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Default Re: 7.5JB-3CR/9804T - Welcome 'red' to the family

I looked at the Genset for a long time and almost bought it on 2 different occasions. I even talked to the guy on the phone about shipping.

I thought it was a good one and I hope for you that it turns out to be.

You should be able to find all of the manuals you need here:

http://www.twinslan.net/~n0nas/manuals/onan/

I have a Westerbeke whose Company color is red. Red is not to bad of a color, but just not on an Onan LOL
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Old 02-28-2016, 08:34:01 AM
Ray Lynch Ray Lynch is offline
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Default Re: 7.5JB-3CR/9804T - Welcome 'red' to the family

Looks like spec T with a magneciter. Built Sept 1970.
Curious to know running condition as that set has been for sale awhile.
Keep posting and good luck wiith it.
Ray
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Old 02-28-2016, 08:48:10 AM
MBB MBB is offline
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Default Re: 7.5JB-3CR/9804T - Welcome 'red' to the family

Sure the model number is correct I see nothing on it as far as a build sheet?
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Old 02-28-2016, 10:52:24 AM
Max Thompson Max Thompson is offline
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Default Re: 7.5JB-3CR/9804T - Welcome 'red' to the family

I found it in the master parts manual. Looks like it should with enclosure & fuel tank as spec.

Should also have amp. meter, low oil & over speed safety's.
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Old 02-28-2016, 10:54:39 AM
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Billy J Shafer Billy J Shafer is offline
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Default Re: 7.5JB-3CR/9804T - Welcome 'red' to the family

Quote:
Originally Posted by Max Thompson View Post
I found it in the master parts manual. Looks like it should with enclosure & fuel tank as spec.

Should also have amp. meter, low oil & over speed safety's.
I thought you were out shooting fake ducks this weekend.
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Old 02-28-2016, 07:36:28 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

I always make time for "chores" here at The Stak. Unlike some slackers who will "nap" right through chore time.
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Old 02-28-2016, 10:03:53 PM
Leon N. Leon N. is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

BStrutton, I have pretty much the exact same machine! The number 9804 connotates the optional equipment and the letter "T" is the factory build revision. The manuals you should have as a minimum are 967-320, the Onan Operator and Parts manual, and 967-500, the Onan JB/JC shop repair manual. These are the two manuals Onan provided to me back in 1969 when I refurbished my 705JB-3CR/4703P. They also contain parts lists, even bolt torque requirements. Those manuals cover the build spec T as well. My JB remains active on standby since 1970. This is perhaps one of the best highly reliable generator plants ever built, the likes of which will never be built again. You have a gem here! Do not attempt to start this JB without first reading the caution note printed on the inside of the control box cover or refer to the owners manual, 967-320.

Last edited by Leon N.; 02-28-2016 at 10:19:43 PM.
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Old 02-28-2016, 11:49:05 PM
BStrutton BStrutton is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

@Leon N,

I grabbed the manual but not seeing a particular caution on startup.. Could you elaborate or point me to it in the manual so I can be thinking about it while waiting for freight?

Thanks all!
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Old 02-29-2016, 08:40:27 AM
Leon N. Leon N. is offline
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Default Re: Onan 7.5JB-3CR/9804T - Welcome 'red' to the family

Yes, I can point you to at least three areas where Onan cautions the installer/user. Looking at your picture, I would presume the magneciter output lead, T2 has already been properly grounded to prevent damage to the exciter. However, here is where you can find more information as well as from looking at the inside of the control box cover as shown below.

967-320, pages 6 & 7 show the generator output lead T2 grounded to the chassis.

Also, 967-500, page 72, look at the top wiring diagram and read the note under the diagram.
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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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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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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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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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