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Another Onan JB


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  #41  
Old 01-08-2018, 09:29:52 PM
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Motorhead Motorhead is offline
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Default Re: Another Onan JB

EnginePat, is the JB only a 4 wire head? The previous owner has the strainer in the gas line on upside down.

I answered my question about the 4 wire gen head. I see it is a 120/240. Nice score
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  #42  
Old 01-08-2018, 09:34:51 PM
EnginePat EnginePat is offline
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Default Re: Another Onan JB

Motorhead,
Yes 4 wire yd , it has a rats nest of wires pulled thru the control box to the junction box as you see them. I had to go back and look at the pic , yes your right it is facing up not down.
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  #43  
Old 01-09-2018, 04:02:53 PM
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Default Re: Another Onan JB

So I spent a couple hours working on the jb, got it to turn over by pushing in the solinoid lever on the starter. No spark that I can see , traced the wiring in the junction box. Looks like remote starter wiring, outlet below junction box wires,and gas feed solinoid. The governor arm was stuck , little pb blaster freed that up. Put some oil in it it was just below the low mark on the stick. I can hear the starting solinoid in the control box click when I hit the start switch but the starter will not pull the plunger in. I think the solinoid on the starter may be bad. So when I turned it over I was watching the oil pressure , it only went to 15psi. So it may be bad or the oil is to thick. So how many psi does it need to get over the low oil shut shut down? To bypass it ?.I pulled the valve cover and the oil is pumping up to the head so the pump is working. Can I jump the coil without cooking it?
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  #44  
Old 01-09-2018, 04:18:40 PM
len k len k is offline
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Default Re: Another Onan JB

15 psi ..... seem to remember something like that on mine while cranking. Mine made 40 while running.

Oil switch , not sure on Onan . On other stuff I saw a lot of low pressure switches for cars around 8 psi. when looking for cheap generic replacement for 5.5kw Generac engine.
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  #45  
Old 01-09-2018, 04:23:31 PM
Birken Vogt Birken Vogt is offline
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Default Re: Another Onan JB

Normally safety switches are set far below what you would consider a normal range. Because you don't want it shutting down falsely in the middle of the night for that one unit that runs on the low end of normal. 8 psi sounds low but that's common.
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  #46  
Old 01-09-2018, 05:23:54 PM
len k len k is offline
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Default Re: Another Onan JB

Got to remember pump oil pressure is not forcing shaft to float on film of oil, it's just supplying oil to main bearings. It's the rotation that forms the hydrodynamic wedge of oil that lifts shaft off bearings
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  #47  
Old 01-09-2018, 05:50:44 PM
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Default Re: Another Onan JB

I ran into that problem when I had just acquired my JB but it would start holding the button and shut down when I let off. I traced it to the electric oil pressure switch that is mounted next to the mechanical gauge. My set has the LOPKO option, thus the sending unit. Anyhow, the sender is supposed to open at about 9psi and mine was stuck closed and kept the coil grounded out. I disconnected the sending unit on mine and it started and stayed running.
Before I installed the new replacement switch, I put it on an manifold with a real accurate mechanical gauge and checked several times the closing and opening pressure. Came up with 9 psi.
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  #48  
Old 01-09-2018, 07:56:01 PM
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Default Re: Another Onan JB

I'll disconnect the oil sensor and see how it goes. This has the low oil pressure shut down option so that may be the problem.

I did see a sensor on the exhaust manifold, what would be the reas on for that?
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Old 01-09-2018, 08:02:33 PM
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Default Re: Another Onan JB

[QUOTE=EnginePat;1451292] Can I jump the coil without cooking it?/QUOTE]

Do you have 12-V to the coil?

Yes, you can jump battery voltage to the coil to test, this will bypass all safeties. You can also jump the starter pull in solenoid to see if it is working.

If the starter solenoid fails to pull in when jumped, you can pull the solenoid and take the end cap off to check the contacts and contact ring within.

Put a test light on the points and see if they are making contact, this is covered in the service manual.

One of the things I love about the J series is that they are so easy to trouble shoot once you understand what the relays in the control box are doing. Remember that the K-12 relay has a 6-V coil when you are "wielding jumper wires".
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Old 01-09-2018, 08:22:42 PM
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Default Re: Another Onan JB

I believe that the sensor on or near the exhaust manifold is an over temp shutdown switch, I have a sensor in the discharge air flow on my JB. I could be wrong with out seeing where the sensor is, but that is my .02 guess

-Bob
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  #51  
Old 01-09-2018, 08:51:31 PM
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Default Re: Another Onan JB

The starter will work if I take a screwdriver and push the bendix lever into the solinoid . But that is not completing the starting circut.
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Old 01-10-2018, 08:24:33 AM
Max Thompson Max Thompson is offline
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Default Re: Another Onan JB

Quote:
Originally Posted by EnginePat View Post
The starter will work if I take a screwdriver and push the bendix lever into the solinoid . But that is not completing the starting circut.
The starter solenoid does not affect the start circuit, but the start relay in the control box does.
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Old 01-10-2018, 09:33:24 AM
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Default Re: Another Onan JB

Thanks Max, I did some searching thru the old threads and that came up a couple of times. I haven't looked at it yet but I'm sure it has contacts in there maybe a little cleaning could be the answer.
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  #54  
Old 01-10-2018, 12:29:21 PM
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Default Re: Another Onan JB

Put a test light on starter solinoid small wire, see if it's get +12 when you press start button.

That solinoid is real low ohms, so might see 100 amps going into just the SOLINOID coil.

Need good wire connections.
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  #55  
Old 01-10-2018, 01:06:42 PM
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Default Re: Another Onan JB

When I get back to look at it I will go over those relays and solinoid. I ordered some deoxit contact cleaner it supposed to work really on oxidized /medium corroded electronic components and connections so I'll give that a try on the jb and the jc starting relay.
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  #56  
Old 01-10-2018, 01:31:19 PM
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Default Re: Another Onan JB

For wire connections I find a wire wheel on a dremal works best. For relay contacts fine sand paper, ~360 . if badly pitted 180.
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  #57  
Old 01-10-2018, 08:54:22 PM
Max Thompson Max Thompson is offline
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Default Re: Another Onan JB

Quote:
Originally Posted by len k View Post
That solinoid is real low ohms, so might see 100 amps going into just the SOLINOID coil..
Very low amperage, all it does is pull in the starter solenoid and feed ignition power while starting.
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  #58  
Old 01-10-2018, 09:17:58 PM
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Default Re: Another Onan JB

I pulled the starter, then removed the solinoid took off the nuts from studs and tapped them in. Took off the 2 screws and removed the cover, turns out the wires that go into the coil are burned off. So I need a solinoid for it.
On the starting relay one of the screw heads was broken off and the 2 wires that go to it were loose. Just unscrewed the broken stud and put a new screw in.
Anyone know the number for the JB starter solenoid?
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Last edited by EnginePat; 01-10-2018 at 09:28:28 PM.
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  #59  
Old 01-10-2018, 09:22:18 PM
len k len k is offline
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Default Re: Another Onan JB

Max ...... was talking about resistance of solenoid on the starter (~ .1 ohm coil resistance to pull in , and then ~ .2 ohm on that solenoid's hold coil) so ~100 amp draw during pull in then ~50 amp to hold.

That explains why they used a hi-amp "starter" relay/solenoid in control box to power solenoid on the starter.

Last edited by len k; 01-10-2018 at 09:33:03 PM.
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  #60  
Old 01-10-2018, 09:22:56 PM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Another Onan JB

The starter solenoid has two windings and two grounds. The pull in winding is grounded through the starter brushes, the hold in winding is grounded to the base. When current is applied to the terminal both windings are grounded, high initial current, the solenoid pulls in supplying current to the brushes, this kills the pull in winding, current drops, the hold in winding is grounded to the base and keeps the starter engaged as long as current is applied. If the brushes aren't making contact the solenoid won't pull in.
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