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Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan 7.5 JB-18R/2731AA Followed me home!


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  #11  
Old 06-18-2017, 05:24:35 PM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Awesome information Leon!
Update, my gen set starts and runs, bad points and cruddy plugs were the cause of the no-start condition. I am getting 108 VAC to 110 VAC across each leg of the 220 vac wiring that this unit has been set to. After taking the nose apart and inspecting the starter motor for grinding at crank, I came to realize I need a new bendix gear for my starter motor and at the very least a new ring gear.I would prefer to locate a good used flywheel instead.
I tested the transfer switch, LTE30-3 1761A, and the contactors are very noisy, (hum) as they sit in standby mode. The exercise clock and return to utility power timer work as hoped.
A question for the moderators, as this thread coveres the generator, will it be better to start another thread for the transfer switch?
Thanks
More pictures to follow...hopefully they will post right side up!
-Bob
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  #12  
Old 06-18-2017, 05:41:10 PM
MBB MBB is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Being they are to separate units one generator another switch it may be easier to follow having separate threads.
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Old 06-18-2017, 06:02:11 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

The ring gear is really that chewed up? That's a bummer!
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  #14  
Old 06-18-2017, 06:44:05 PM
Leon N. Leon N. is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

EICBob funny you are having so TR with the starter. I had similar problems with my JB stater. My flywheel ring gear also had rounded of (worn) teeth on one side. I had starting problems like, I think, you are mentioning. THe JB would start to crank, catch and sputter a bit, then the bendix would briefly drop out, then re engage, grinding gears and just a horror show. That scenario was aggravated by a couple of things that I finally figured out after replacing the bendix. #1, the electrical contacts in the stater shifting solenoid were worn and making intermittent contact at times. This was aggravated by a relatively weak starting battery. #2, A less than perfectly adjusted Carburetor hi-speed natural gas jet and by a weak ignition condenser.

Some days it would start perfectly OK! But many times I had to play with it to get sufficient cranking speed, even with the controls set for hand crank.
Fineally after taking the shifting solenoid apart, and noticing the severely worn electrical contacts, worn to,the extent I could not turn them over and use the other side, I took the starter to an auto electric shop and they rebuilt it with a new shifting solenoid and it has worked pretty much OK since what 1975 or there a outs. I have some pictures if interested of the worn solenoid contacts.

NOw the way that starter solenoid shift drives the starter pinion gear into the ring gear with one loud positive clunk, you probably do not need to replace the ring gear. Good Luck.
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Old 07-03-2017, 08:50:13 AM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Update.....
I replaced the bendix gear on my starter, cleaned out all the dirt and gunk and re-lubed the solenoid fork and pivot points. Took a hand file to the ring gear and dressed up the teeth a bit and took down the curled high spots. Put it all back together and 90% of the grinding, thrashing and overall nastiness has ceased!
I am still on the lookout for a good flywheel with ring gear, but am happy with the intermediate outcome.
I had to replace, read create from various parts, the 4 rubber control box mounts so the box would stay put and not vibrate and bounce around. I used 4 automotive shock absorber rubbers and 4 1/4-20 "J" nuts to fashion new mounts. The control box is now happy and solidly mounted to the generator housing again.
I need to come up with a way to accurately measure the RPMs of this unit, to verify the governor settings and the carb settings, any ideas?
I have fashioned a monitor panel for testing and so far I like what I am seeing
I have a short video of the unit in operation, just need to post it some where for your viewing enjoyment.....
More later as this project continues!
Thank you all for your kind assistance!!

-Bob
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  #16  
Old 07-03-2017, 08:56:30 AM
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Troll Troll is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Measure the output frequency as 60hz is 1800rpm on that set.
It
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Old 07-03-2017, 08:59:42 AM
Dale Russell Dale Russell is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Buy a Kill A Watt Meter which can be found at most of the big box stores or on line. It will show Hrz, Volts, Amps & ETC. for around $25.00. This is what mosthere use to set the Hrtz. Haves fun!!!
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Old 07-03-2017, 09:01:23 AM
Pauls12 Pauls12 is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

http://www.ebay.com/itm/LCD-Digital-...JWrH2T&vxp=mtr this is what I use on my panel.
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Old 07-04-2017, 07:06:40 PM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Here is a YouTube link to my son's account where my short video of the JB running is posted...
https://m.youtube.com/watch?feature=...&v=MZ3zHR13Ku0

Happy 4th!!!
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Old 08-14-2017, 10:52:42 AM
EICBob EICBob is offline
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Default Re: Onan 7.5 JB-18R/2731AA Followed me home!

Good Monday Morning
I spent the weekend finishing up some of the wiring on my monitor panel and some more testing of my JB.
I have come across an issue that has me a bit confused. Upon initial start up the voltages across the 2 legs will either be low, at around 90 VAC, or they will be high, in the area of 135 VAC. These voltages are with out any load on the generator. I see them at the monitoring panel as well as measuring them with a good DVOM at the output lines of the set.
My original thought was a cranky voltage regulator board. What has me a little less sure about the VR is this, if I stop the generator and restart it, 9 out of 10 times the voltages will then be at 120 to 122 VAC and remain there.
I ran a 90 minute load test with 2000 watts on each leg and the unit ran smoothly and the voltages never varied more than 2 or 3 volts.
Ideas?

Cheers!!
-Bob
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