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Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan 7.5 JB-5DR/174440AA


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  #1  
Old 11-14-2017, 09:25:58 PM
RETCPO RETCPO is offline
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Default Onan 7.5 JB-5DR/174440AA

Looking at a generator and could use some help.
ONAN 7.5 JB-5DR/174440AA
Serial NO E770237484

What does the 5DR stand for? (3 phase?)
Manufactured MAY 1977
SPEC AA

Any other information that can be gained from the collective mines?

Respectully
Keith
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  #2  
Old 11-14-2017, 09:30:21 PM
Wayne 440 Wayne 440 is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

https://www.smokstak.com/forum/showthread.php?t=119313

120/240 3 phase, 4 wire
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Old 11-14-2017, 09:32:43 PM
Chas183 Chas183 is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Voltage codes are here.
https://www.smokstak.com/forum/showthread.php?t=119313

Looks to be 120/240 3 phase 4 wire.

Just little further down Kevin K has a nice PDF for download.

chas183
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Old 11-15-2017, 02:28:05 AM
Ray Lynch Ray Lynch is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Spec AA is a YD gen end.
Ray
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  #5  
Old 11-15-2017, 07:01:25 AM
MBB MBB is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

I believe you have 1 to many 4s in the model number. Here is the build sheet for the unit. Very desirable. 4Wire. B150 extended Stack. (Had to go back and check I never saw a 4 wire with extended stack. Usually they are 12 wire.) No need to de-rate for single phase. It also has a meter panel and Housed providing its all there.
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Last edited by MBB; 11-15-2017 at 07:39:23 AM.
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  #6  
Old 11-15-2017, 09:25:49 AM
RETCPO RETCPO is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

MBB you're right!
7.5 JB-5DR/17440AA
Serial NO E770237484
Fat fingers and not proof reading strikes again...
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  #7  
Old 11-15-2017, 09:56:36 AM
MBB MBB is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Don't know the condition or price but it's a good one.
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Old 12-03-2017, 09:07:18 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

I had been watching this one for a month or more, but do not need another Onan, and since I was "cured" of the Green Disease some time ago I saw no need to even call about it.

Then RETCPO gives me a call: he would like to have this one for his mother's place, about 20 miles from me. How could I say no, it is for his "mother".

The story so far is below and pictures are here https://www.smokstak.com/forum/album.php?albumid=1546

Got the JB home Monday, got around to looking it over about Wed. Got the bulk of the mouse nest and trash vacuumed and blown out.

Contrary to the ad, the motor was not free. Water in both cylinders. I blew it out and added a cup of PB Blaster to each and let it sit a day or so. With a little persuasion it broke loose and seemed smooth rolling over. Just checked and showing #135 on no. 1 and #130 on no. 2 cylinders, so I do not think the water did any serious damage.
Made wiring repairs that “had to be done”, cut the outlets loose and removed the VR board, ”temporary” new oil and filter(cheap straight 30 wt. and a FL1 A filter). After a little fight with the points she came to life on carb cleaner. Hooked up a boat tank and she runs on her own. Let it run till she smoothed out and I was sure it was a runner then put the VR back in, makes good power.

Now I know it is a keeper, so will proceed with replacing control box wiring and relays, the relays are in sad shape. I may hook the load bank up and let it run an hour or so before I tear into the control box.

It is a 12 lead gen-end, wired “down” to 4 tagged leads. I will rewire to single phase before load banking it.
Sunday:

Today:

Changed out the 30 amp twist lock receptacle for a 4-wire 50 amp and reconfigured T-leads to 120/240 single phase. Replaced oil # gauge, the old one was sluggish. Greased the gen-end bearing. Rigged up a temporary exhaust.

Fired it up and let it warm for 15 min, plugged in the load bank and loaded it up to about 30 amps per leg. Ran for ½ hr. or so and seemed good but Hz were at 58 so after tweaking the carb to get the maximum Hz. I gave the governor about ¼ turn. No load = 61.6 Hz, full load 59.5 Hz @ 237 volts, recovery is very good from 6 amps to full load. I think this is close enough. It ran under full load for 2 ¼ hr. and never faltered. I think this one is a keeper.

While the JB was running, I moved 2 JCs from the floor of the shop to the loft in the barn and the trailer mounted JC to the barn with the other trailer mounted RJC. My help will be proud of me in the morning to see a little more floor space in the shop.

Shut the JB down at 4:30 and let it cool, then gave it a bath, won’t make it run any better, but more pleasant to work on. It is parked in the back of the shop until I get to the control box..
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Old 12-10-2017, 07:43:34 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Made some progress this week. My conscience would not let me put new relays and controls in the old mouse hotel so I sand blasted and painted the inside and bottom leaving the front original to match the rest of the set.

Replaced the rectifier and heat sink, start / stop switch, both relays and any wires or terminals that were “suspect”.

Starts, runs and now charges the battery.
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Old 12-10-2017, 08:32:15 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

MAX,

You TRULY are one of the Kindest Gentleman I know!!!!!
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Old 12-10-2017, 09:46:53 PM
DMeed DMeed is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Quote:
Originally Posted by Max Thompson View Post
Made some progress this week. My conscience would not let me put new relays and controls in the old mouse hotel so I sand blasted and painted the inside and bottom leaving the front original to match the rest of the set.
Are those two relays the same, or is one 6v and the other 12v?

Should I add the hold downs for the relay sockets?

Any particular reason to switch to the cube relay for the start over the original solenoids? Original Solenoid looks like ?$25 vs about $12-14 for the cube relay and socket. Is price the only consideration?


I'm trying to decide between rewiring my JC mouse hotel with all 12v relays or staying with the 6v K12 run relay + resistor setup.


I don't have the LOP reset switch (melted) so I'm thinking since I've got to replace that, I may as well rewire everything to 12 v. Like the idea of having all the relays the same in the set, so they can be interchanged and only have to carry one type of spare.

On the other hand it would be nice to stay close to factory so anyone who follows can figure out what is going on.


To replace the LOP I looked at time delay relays, but it looks like they are up close to $100. Thinking now of using someone's idea of putting in a 10 amp breaker for the LOP reset and adding a relay/resistor to put a 12-15 amp load across it when the oil pressure drops so it pops, but not right away.

Last edited by DMeed; 12-10-2017 at 09:57:24 PM. Reason: rewording
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Old 12-11-2017, 08:05:34 AM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Quote:
Originally Posted by DMeed View Post
Are those two relays the same, or is one 6v and the other 12v?

Should I add the hold downs for the relay sockets?

Any particular reason to switch to the cube relay for the start over the original solenoids? Original Solenoid looks like ?$25 vs about $12-14 for the cube relay and socket. Is price the only consideration?

The ignition / start disconnect relay is a 6-V coil. I do not know, but suspect Onan used a 6-V coil since the set is shut down by "shorting" this relay coil to ground to open it. The start relay is 12-V.

The hold downs for the relays could not hurt anything, I need to get some.

I switch the start relay to a cube for convenience, I can keep a spare on hand for $12 and switch it out in a minute or 2 if needed with no tools.

I will admit that changing the relays out may make someone in the future scratch their head a little, but I doubt no more than I did the first time I tried to understand the OEM set up . The contacts and function of the K-12 cube style relay is the same, only the positions of the screws changes. I hope the enclosed relays will be more immune to mouse pi$$ and dirt.
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Old 12-11-2017, 08:53:23 AM
Kevin K Kevin K is offline
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Default Re: Onan 7.5 JB-5DR/174440AA

Take a look at Amazon or Ali express for a time delay relay. I do not have a JB or JC to test, but I'm sure with a little work you can find a suitable device.

Amazon mini time delay relay for $22:
https://www.amazon.com/Timer-Delay-R.../dp/B00PD65UGA

For better prices check Ali express. A quick search shows lots of options:
https://www.aliexpress.com/wholesale...me+delay+relay

How about $1.40 for a module?
https://www.aliexpress.com/item/High...StoreLevelAB=0
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Old 12-11-2017, 08:56:58 AM
DMeed DMeed is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Quote:
Originally Posted by Max Thompson View Post
The ignition / start disconnect relay is a 6-V coil. I do not know, but suspect Onan used a 6-V coil since the set is shut down by "shorting" this relay coil to ground to open it. The start relay is 12-V.
A few people have dissed the 6v design thinking it is old-fashioned, but I have to admire the elegance of a design that can get by with one relay and an inexpensive resistor to do the job that would require two relays in a 12v design.


Quote:
Originally Posted by Max Thompson View Post
... I hope the enclosed relays will be more immune to mouse pi$$ and dirt.
Has anyone ever seen a mouse nest _under_ the control box against the generator housing? I see in your pictures what looks like a mud-dauber nest in there.
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Old 12-11-2017, 10:48:13 AM
reid070 reid070 is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Quote:
Originally Posted by Max Thompson View Post
Made some progress this week. My conscience would not let me put new relays and controls in the old mouse hotel so I sand blasted and painted the inside and bottom leaving the front original to match the rest of the set.

Replaced the rectifier and heat sink, start / stop switch, both relays and any wires or terminals that were “suspect”.

Starts, runs and now charges the battery.
Max very nice job! Quick question , what is the purpose of the small terminal strip over behind the 12 volt start relay? (In the corner of the control box)

Steve
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  #16  
Old 12-11-2017, 07:18:57 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5 jb-5dr/174440aa

Quote:
Originally Posted by reid070 View Post
Quick question , what is the purpose of the small terminal strip over behind the 12 volt start relay? (In the corner of the control box) Steve
The original start relay has 2 wires (1 #12 ga.) going to the B+ terminal and the coil is internally wired. It is also a 3 pole contactor, contacting B+, S, & 1 terminals when pulled in.

The connections to the relay base will readily accept those 2 wires, but since the coil is not internally wired and I also have to use "jumpers" to provide B+ to the 2 contact connections this makes a total of 5 B+ connections which is way too much wire to stuff under the relay base connection, so the piece of terminal strip gives me a place to make the connections neatly.
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Old 01-14-2018, 12:24:10 PM
Max Thompson Max Thompson is offline
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Default Re: Onan 7.5 JB-5DR/174440AA

Well, I think RETCPO’s JB is ready for service at “Mom’s” place. I have been through it from top to bottom, short of tearing into the engine, though I did torque the head bolts and set rocker arm clearance. The control box redone, starter gone through, “tune up” items all replaced, new diaphragm on points plunger, new mounting cushions under both ends, new gaseous carb and gas piping installed, exhaust rerouted with flex section. It got very little “cosmetic” work done other than the control box pan, otherwise, just a good bath.

If it will hold together for another hour, it will have completed a 24 hr. test run at 2/3 load. I have run it at full and a little over load several times before I reconnected the meter panel that has the old 25 amp 3 pole breaker in it.

I added some more pictures to the “album” here https://www.smokstak.com/forum/album.php?albumid=1546 Sorry, they are not in any logical order. I have not found a way to rearrange pictures in an album yet.

PS; Oil consumption after 24 hrs. 0

Last edited by Max Thompson; 01-14-2018 at 07:24:50 PM.
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Old 01-14-2018, 01:30:57 PM
JohnnyC JohnnyC is offline
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Default Re: Onan 7.5 JB-5DR/174440AA

Very nice thread. I don't know how I missed it until now. Great work and updates.

JohnnyC
New Jersey
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Old 01-14-2018, 09:35:37 PM
EnginePat EnginePat is offline
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Default Re: Onan 7.5 JB-5DR/174440AA

Nice job! A 12 wire jb that's nice.
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