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Onan JB Thermomagnetic Choke


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  #61  
Old 09-03-2017, 05:58:03 PM
Max Thompson Max Thompson is offline
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Default Re: Onan JB Thermomagnetic Choke

Quote:
Originally Posted by Leon N. View Post
Max re your comment: "Your lifting bracket may be an older style." If you call my 1966 built JB the old style, so be it. All I am saying is that his comment about "two bolts" in post 52 does not compute to me. Two bolts, albeit the rocker cover bolts will not support the JB as the author seems to think. No way. There must be more to it.
Yes Leon, I am afraid I am calling your (and many more of our) J series "OLD". Your JB is 10 years younger than I am and I am feeling pretty old today.

The parts break down Kpack posted and the picture I linked are to a later model lifting bracket. I suspect that the later bracket will disperse the weight more evenly across the valve cover than the single bolt style you have.

No disrespect to the older style J series that many of us own. But Onan did "improve" their design as the model progressed, like adding auto field flashing to the "later" model magniciter sets.
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  #62  
Old 09-03-2017, 06:50:56 PM
len k len k is offline
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Default Re: Onan JB Thermomagnetic Choke

Leon .....2 bolts for lifting....... I have not looked at it recently but I think those two bolts go into the cast iron? head. If so, thread pull out strength of cast iron is likely ~ 2-3X than that of aluminum (depending on alloy), assuming same thread size and one bolt.
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  #63  
Old 09-03-2017, 07:29:16 PM
Leon N. Leon N. is offline
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Default Re: Onan JB Thermomagnetic Choke

Len K ok if you say so. There is a lot of advice kicking around. The refurbished should also try to get his hands on the owners manual and parts list for his plant to verify the plants design requirements.
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  #64  
Old 09-03-2017, 07:39:49 PM
KPack KPack is offline
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Default Re: Onan JB Thermomagnetic Choke

967-0223 jb parts manual
https://www.dropbox.com/s/7s6nw230d1...-0223.pdf?dl=0
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  #65  
Old 09-03-2017, 09:27:39 PM
JoeE. JoeE. is offline
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Default inside rocker cover

The bulbous protrusion in the center of the photo shows what the ½" bolt threads into down in the rocker cover.
It is gusseted in two places out to the side of the cover.

Even with that, that cover is just die cast aluminum and I'd wager it is not very thick in cross section... I bet the all the flat surfaces are no more than 1/8" thick, at most. The mounting flanges are about a ¼" thick.

So, even with all that.. I wouldn't feel real safe lifting the whole machine via the lifting bracket depending on die cast alum. holding it secure. I'd be afraid the aluminum would tear out. I know that they say that's how to do it, but I'm not in favor of it.

I'd be more liable to lift by a bracket that straddled the entire rocker cover and had feet that fit down where all 4 of the 5/16" bolts are threaded into the cylinder and the bolts went through those. Not going to make one, but that'd be safer, to me.

Plus... from the looks of things, when you lift at that bracket, doesn't the whole contraption tilt back towards the generator end? Looks off center, to me.

I'm thinking of making a lifting beam that has one hole where the ½" bolt goes in the rocker cover, and have a "sling" sort of thing of the other end that would go around the generator housing... then, put the lifting eye back towards the gen. end.
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  #66  
Old 09-03-2017, 10:18:23 PM
len k len k is offline
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Default Re: inside rocker cover

Quote:
Originally Posted by JoeE. View Post
The bulbous protrusion in the center of the photo shows what the ½" bolt threads into down in the rocker cover.
It is gusseted in two places out to the side of the cover......
Good that the alunium hole is threaded for such a long length. Have not run the numbers but that should help increase pull out force by reducing aluminum female thread shear stress.

Usually in bolt stress analysis you assume 3 threads take the force. Think this applies when bolt and nut are same material. But aluminum being ~ 3 times more compliant ( springy, ) than steel bolt should allow the force to be spread over more treads ( lowing thread stress, and allowing larger bolt pull force before thread pull out)

Still I remember Yoda saying lift genset only , no skids, bats, or fuel tank.

But as Leon says.......read the manual.
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  #67  
Old 09-04-2017, 05:16:00 PM
Leon N. Leon N. is offline
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Default Re: inside rocker cover

Obviously you can do,what you want, but for me I follow the Onan lifting procedures and have had no problems. Yes, I also feel a bit queezy nsupporting the entire JB through that one lifting hole. Even when lifting the JB using the hole closest to the generator, the JB tilts down somewhat. The beck end is heavier than the front end and the bracket is not located at the center of gravity. I left my JB hanging for three days while the starter was out for repair. No problems with the bracket. I did retorque the four rocker cover bolts and the bracket bolt before attempting the lift.
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  #68  
Old 09-04-2017, 11:01:49 PM
JoeE. JoeE. is offline
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Default Timing marks

I'm just looking over everything so I'll be familiar with everything when it goes back together.

I pulled a plug out, got the front cylinder coming up on compression.
I cleaned off the outside diameter of the flywheel. It was rough surface cast iron. I wire wheeled it to accentuate the hash marks, and hopefully whatever numbers and letters are stamped in the periphery of the flywheel by the hash marks.

With the piston at TDC, the flywheel is setting as shown in the first photo. I can't really make out what all they've got stamped in the iron. I painted the "pointer" silver to highlight it.

From reading the service manual.. I'm thinking I've seen 55, 25 and 5...but I'm not sure. I really can't make out TDC or even TC anywhere.
The letters and numbers are not very well stamped. In the first photo, I've numbered 5 arrows 1 thru 5, so if you know which ones are which, you can put those details in a reply.

The second photo shows another "pointer" that is integral cast into the aluminum governor housing and viewed from the top.... None of the timing hash marks seem to correspond with any position of the piston when judging them by this pointer.

Like I've said... this thing ran when he quit using it.. I'm not taking anything apart, so it all ought to still be in time.. I'm just looking things over while it's apart so I'll have an idea what to look for if it ever needs ignition work.
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  #69  
Old 09-04-2017, 11:10:05 PM
JoeE. JoeE. is offline
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Default Ignition mechanism

In this photo, I took the points cover to see what it looked like in there. Nice and clean.

Is what I have the red arrows pointing to supposed to be a "kill switch"? There was no hole or button in the timing cover to actuate this. One of the arrows points to a wire coming from that assembly, it passed out from under the breaker cover and went nowhere... not connected to anything.

They have two condensers in this circuit.. they're indicated by the yellow circles. One mounted inside this cover and the other was held by a bolt that held the ignition coil to the block. I'm thinking that the inside/original one went bad and since this was mounted in a hard to get at location, they may have just added an external one and be done with it.
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  #70  
Old 09-04-2017, 11:40:12 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan JB Thermomagnetic Choke

In the first picture on post 68, You have the correct timing pointer in that picture, as shown it is lined up with the "5 degree Before Top Dead Center" mark.
The next ring gear tooth down is the TDC mark and the next tooth down from there is the "5 degree After Top Deac Center" mark.

5 teeth above the mark where the pointer is "25 degrees Before TDC" mark and two and 1/2 teeth further up is the 35 degree "BTDC"

To top that off, 13 teeth After the "5 degree After Top Dead Center" mark is another mark which is 55 degrees AFTER TDC. You would have to turn the flywheel in direction of rotation "arrow cast into the flywheel" to see this mark.

---------- Post added at 09:40:12 PM ---------- Previous post was at 09:25:28 PM ----------

Your other picture of the centrifugal switch.

There are two sets of contacts, Your circled condensor sitting in the switch is for the points that sit right above it "the sey of points that actually look like an actual set of points.
The two arrows pointing to a set of contacts again in the switch point to the run contacts. These run contacts are supposed to close about 900 RPM, If you do not hold the start switch long enough to let it get to at least the 900 RPM and let off the start switch the set will just stop. The contacts need to close to energize the run relay within the control box. Once the contacts close and energizes the run relay, the run relay automatically kicks the starter relay out and also puts constant voltage to the coil circuit.

I hope I did not confuse you with this!
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  #71  
Old 09-05-2017, 12:39:52 AM
Ray Lynch Ray Lynch is offline
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Default Re: Onan JB Thermomagnetic Choke

The disconnect switch shown in post #69 picture looks broke or badly out of adjustment. It's contacts should be gapped to .020".
Ray
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  #72  
Old 09-05-2017, 01:48:30 AM
Leon N. Leon N. is offline
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Default Re: Onan JB Thermomagnetic Choke

I agree with everything said in posts 70 & 71 except the reference to the 55 degree timing mark. I think the reference to the 55 degree Mark is incorrect. Why would anyone care about 55 AFTER TDC.

You can see a picture of these timing marks on the flywheel be referring to the Onan repair manual, 967-500 which you should have. I can email you a copy if needed.

Yes there are two condensers in the circuit The one shown is at the points because it suppresses the sparking at the points. Test is with an ohm meter. IT should not be leaky but register way over 100 megohms. The other condenser should NOT be tphysically there. IT should be located off the ignition coil on the deck. Refer to your wiring diagram foe its' exact circuit location. Once again your "control" wiring diagram is listed on the factory build sheet and a copy may be in 967-500. Excellent questions and pictures!
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  #73  
Old 09-05-2017, 09:31:45 AM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan JB Thermomagnetic Choke

Leon, I do not know why the 55 degree ATDC mark is there? I just pointed it out because it's distinctly there and marked on the JB flywheel that I had in my hand when I answered his questions.
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  #74  
Old 09-05-2017, 09:53:16 AM
Ray Lynch Ray Lynch is offline
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Default Re: Onan JB Thermomagnetic Choke

967-0500 page 29 says to rotate flywheel to the 55 deg. mark when setting ignition breaker point gap.
Ray
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  #75  
Old 09-05-2017, 09:55:58 AM
Dale Russell Dale Russell is offline
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Default Re: Onan JB Thermomagnetic Choke

Could it be that, that is the point where the Exhaust Valve would start to OPEN for timing purposes?
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  #76  
Old 09-05-2017, 10:15:26 AM
Leon N. Leon N. is offline
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Default Re: Onan JB Thermomagnetic Choke

Gents I think I know the answer about the 55 degree ATC mark. if you look at the situation of how the breaker points operate you will find the points are OPEN for a part of each revolution. Do the breaker points reclose at the 55 degree ATC point in the revolution to re- charge/store energy into the ignition coil and then they open at the desired set point at which point the spark occurs at both plugs. I went through a JB operating period way back when using conventional oil that the point plunger hung up in cold weather and the JB would not start due to a stiff oil seal around the point plunger rod. So in the Winter I would always manually rotate the flywheel until the points were closed. That way, the machine would readily start on a cold day. You cannot imagine what a PITA that was. That anomaly disappeared when I switched to Mobile One synthetic oil.

On a related matter. I cannot readily find any garage, Auto Zone, Advanced Auto Supply, Taylor rental or even my local mechanic (who incidentally no longer uses or has a timing light), so I have a question. If the JB ignition timing advance does not work, how do I verify this and can I advance the stopped timing to 35 degrees BTC and will I be able to start the machine?

Last edited by Leon N.; 09-05-2017 at 10:24:11 AM. Reason: Added info
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  #77  
Old 09-05-2017, 11:04:55 AM
Dale Russell Dale Russell is offline
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Default Re: Onan JB Thermomagnetic Choke

Harbor Freight Has a Timing Light for $29.99 which I bought & it has the Dial on it to check the actual timing. Plenty good enough for occasional use.
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  #78  
Old 09-05-2017, 12:13:00 PM
Wheel1943 Wheel1943 is offline
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Default Re: Onan JB Thermomagnetic Choke

Dale, I also just last week purchased a new timing light from harbor, have not taken out of package to even look at it. My original that I had for 3o years up and took flight, or I loaned it and never got it back. Will have to check this new one sometime this week. Must be the same as yours, as mine was also 29.99. Geo
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  #79  
Old 09-05-2017, 02:08:19 PM
Dale Russell Dale Russell is offline
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Default Re: Onan JB Thermomagnetic Choke

Yes, I have been down that road, loaning tool's and not getting them back then forgetting who I loaned them too. Then I had a whole tool box full of tool's stolen. Try to remember what is in your tool box after 50 years of accumulating for insurance purposes. Every time I need a tool and can't find it, O YEA! That was in that bunch of tool's that was stolen! Grrrrrr!
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  #80  
Old 09-05-2017, 02:08:27 PM
JoeE. JoeE. is offline
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Default Re: Onan JB Thermomagnetic Choke

I took a couple of pictures of the "switch" .. its not supposed to be bent up like that, is it?
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