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ONAN JB 7.5 new life


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  #21  
Old 03-10-2017, 04:09:51 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

Quote:
Originally Posted by Leon N. View Post
I went out and took a picture of my JB fuel pump to see if it was leaking oil. Guess not. JB has been in operation since 1970. You may want to think twice about using an electric fuel pump WRT the mean time between failure (MTBF). Obviously you would want a high quality device.
It may not be leaking, but it sure looks like the bolt is loose. Maybe not.
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  #22  
Old 03-10-2017, 04:12:37 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by HBSaunders View Post
was about to bid on that one but was hoping to come up with a decent diesel, keeping my eyes open for one closer to home,howard
I'm glad you didn't. Hope you find you a good diesel.
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  #23  
Old 03-10-2017, 04:49:04 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by Max Thompson View Post
That is a pin that the pump pivots on. I have had "some" luck using a punch to expand the ends of the pin to stop the leak. My preferred option is to block off the mech. fuel pump and add an electric fuel pump.
I found a cut away of a smilar pump. The pin I have marked with an arrow, if I see it correctly. Is that pin just pressed in there and over a lot of usage works its self loose. I guess is its suppose to be stationary or TIGHT.
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  #24  
Old 03-10-2017, 05:24:22 PM
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Default Re: ONAN JB 7.5 new life

I would Check the operation of the crankcase breather. Could possibly be partly plugged or inoperable causing excessive crankcase pressure forcing oil out of the fuel pump pin. Some sets that have seen gaseous fuel service will accumulate sludge around the check valve causing it to stick.
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  #25  
Old 03-10-2017, 05:28:09 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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I would Check the operation of the crankcase breather. Could possibly be partly plugged or inoperable causing excessive crankcase pressure forcing oil out of the fuel pump pin. Some sets that have seen gaseous fuel service will accumulate sludge around the check valve causing it to stick.
Thank you. I was planning on checking that just hadn't got around to it.I'll check it right now.
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  #26  
Old 03-10-2017, 07:38:58 PM
Max Thompson Max Thompson is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by fisherman81654 View Post
I found a cut away of a smilar pump. The pin I have marked with an arrow, if I see it correctly. Is that pin just pressed in there and over a lot of usage works its self loose. I guess is its suppose to be stationary or TIGHT.
Yes, the pump arm pivots on this pin.
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  #27  
Old 03-10-2017, 08:42:18 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by BRae View Post
I would Check the operation of the crankcase breather. Could possibly be partly plugged or inoperable causing excessive crankcase pressure forcing oil out of the fuel pump pin. Some sets that have seen gaseous fuel service will accumulate sludge around the check valve causing it to stick.
The inside of the crankcase breather looks new.
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  #28  
Old 03-10-2017, 09:05:27 PM
Ray Lynch Ray Lynch is offline
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Default Re: ONAN JB 7.5 new life

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Last edited by Ray Lynch; 03-10-2017 at 10:36:38 PM.
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  #29  
Old 03-11-2017, 01:25:06 PM
Leon N. Leon N. is online now
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Default Re: ONAN JB 7.5 new life

Fisherman I checked that fuel pump bolt and it is not loose as you thought in post 21
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  #30  
Old 03-13-2017, 07:20:58 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

I had to order a new valve pan gasket and it came in today.
I installed the gasket and started it up and run fine.
Ok I put a inline filter before the bowl filter just to keep it from getting dirty.
Started it up, NOT. It would not start. After quite a few attempts it got fuel to the new filter. Still would not run. Took the bowl off the carburetor and cranked it, gas came out in bowl area. Put it back together and still the same problem. Checked plugs, nice blue arc on both and both had no fuel on them.

I tried starting fluid and that seem to flood it out.
When I crank the engine over it try's to run but dies out as soon as you release the start button. Also during this process I have to manually hold the choke throttle open or it wont hit at all.

Makes no sense, all I did was add a filter and later I took the filter out that I added, no luck. Fuel pump suddenly not enough pressure? A relay suddenly fail? A air lock? I don't know.
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  #31  
Old 03-13-2017, 07:36:20 PM
Max Thompson Max Thompson is offline
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Default Re: ONAN JB 7.5 new life

[QUOTE=fisherman81654;1370227]
When I crank the engine over it try's to run but dies out as soon as you release the start button. Also during this process I have to manually hold the choke throttle open or it wont hit at all.QUOTE]

Check the ignition / start disconnect relay in the control box and the centrifugal switch under the domed cover by the oil filter.

The service manual has a drill down chart you might look at.
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  #32  
Old 03-13-2017, 08:25:14 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

[QUOTE=Max Thompson;1370235]
Quote:
Originally Posted by fisherman81654 View Post
When I crank the engine over it try's to run but dies out as soon as you release the start button. Also during this process I have to manually hold the choke throttle open or it wont hit at all.QUOTE]

Check the ignition / start disconnect relay in the control box and the centrifugal switch under the domed cover by the oil filter.

The service manual has a drill down chart you might look at.
I know nothing about the centrifugal switch, I didn't know it had one.
I'LL wait and see what this snow does and then try and see what's going on.
I just wanted to get some ideas ahead of time. Thanks....
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  #33  
Old 03-14-2017, 06:51:27 AM
Max Thompson Max Thompson is offline
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Default Re: ONAN JB 7.5 new life

[QUOTE=fisherman81654;1370258][ I know nothing about the centrifugal switch, I didn't know it had one.

I'LL wait and see what this snow does and then try and see what's going on.
QUOTE]

Might be a good day to get the manuals out and do some reading.
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  #34  
Old 03-14-2017, 08:08:55 AM
squidtrap squidtrap is offline
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Default Re: ONAN JB 7.5 new life

Fisherman-if thats all u did was gasket and filter, is it possible fuel line is rotted, or has a small crack? Or pin is worn to the point of sucking air?

It does sound like what Max mentioned but kinda weird it would fail after what u did.

Also i just got my JB and sinse its been so cold have read manuals before hand so when i get to the things i may encounter, or are going to be doing i am familiar ahead of time. 967-500 and 967-320 should have everything u will need and both have very much the same stuff.
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  #35  
Old 03-14-2017, 11:52:18 AM
len k len k is offline
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Default Re: ONAN JB 7.5 new life

DO have to hold start switch till engine rpm comes up enough for centrifical switch to pull in. Read manual but think it activates at ~ 900 rpm
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  #36  
Old 03-14-2017, 02:43:57 PM
fisherman81654 fisherman81654 is offline
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Default Re: ONAN JB 7.5 new life

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Originally Posted by len k View Post
DO have to hold start switch till engine rpm comes up enough for centrifical switch to pull in. Read manual but think it activates at ~ 900 rpm
Not sure I'll read it later have to go back out for now.
If that's the case maybe the battery wouldn't crank it fast enough to get the rpms desired. Getting a new battery today as that one had a dead cell.

---------- Post added at 02:42:40 PM ---------- Previous post was at 02:40:47 PM ----------

Quote:
Originally Posted by squidtrap View Post
Fisherman-if thats all u did was gasket and filter, is it possible fuel line is rotted, or has a small crack? Or pin is worn to the point of sucking air?

It does sound like what Max mentioned but kinda weird it would fail after what u did.

Also i just got my JB and sinse its been so cold have read manuals before hand so when i get to the things i may encounter, or are going to be doing i am familiar ahead of time. 967-500 and 967-320 should have everything u will need and both have very much the same stuff.
The fuel line is new.
Thanks for the info on the manuals, Ill look then up later this evening.
Agreed its weird .

---------- Post added at 02:43:57 PM ---------- Previous post was at 02:42:40 PM ----------

[QUOTE=Max Thompson;1370383]
Quote:
Originally Posted by fisherman81654 View Post
[ I know nothing about the centrifugal switch, I didn't know it had one.

I'LL wait and see what this snow does and then try and see what's going on.
QUOTE]

Might be a good day to get the manuals out and do some reading.
yes a good day when time permits.
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  #37  
Old 03-14-2017, 02:54:56 PM
Leon N. Leon N. is online now
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Default Re: ONAN JB 7.5 new life

This threads author describes a newer version of the JB and one with a YD back end. There must be a newer or more recent version of the proper Onan Operators Manual and Parts List than 967-320. Yes, much of it may apply but thee PLs and the magneciter info obviously does not. Similarly for the JB/JC major overhaul manual, 967-500.
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  #38  
Old 03-14-2017, 04:04:37 PM
len k len k is offline
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Default Re: ONAN JB 7.5 new life

Starter won't bring it up to ~ 900 rpm, engine has to run at least partially to get it here.

When I got my JB the engine would skip and sort of run but would die when I released start button. I just had to hold start button longer till engine decided it wanted to run. Engine had been stored for few years.

For now just drive your car up to it and jumper cable your bat off the running car. Let car charge your bat for ~ 5 minutes first. Car alternator will keep it up enough. Only let starter crank for maybe 10 seconds then let it cool or 30-60 seconds, don't want to cook starter windings. Feel starter temp with your hand.

Last edited by len k; 03-14-2017 at 04:25:04 PM.
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  #39  
Old 03-14-2017, 04:11:29 PM
Leon N. Leon N. is online now
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Default Re: ONAN JB 7.5 new life

Len K that is true unless you have the hand crank switch temporarily on.
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  #40  
Old 03-14-2017, 04:21:02 PM
len k len k is offline
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Default Re: ONAN JB 7.5 new life

Forgot about that, I have spec AA no hank crank switch on it. His is spec AD , might be same , don't know

I just re-read the thread , try dribbling some gasoline down carb throat then cranking it. You said you took carb bowl off but didn't say you took jets apart to clean them, nor blew out the carb. I've taken my JB carb and many others apart to clean them. I've never installed new parts and they all ran fine afterwards.

When I first worked on my JB the carb was clogged. I made up a squirt bottle (shampoo bottle) with a VERY fine tube to restrict flow of gas. I was able to keep engine running by SLOWLY trickling gasoline down carb throat for a test run, even though carb did not flow any gasoline.

Last edited by len k; 03-14-2017 at 04:31:43 PM.
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