Generators and Motors
[Home] - [HELP] - [Forums] - [Library] - [Photo Gallery] - [Groups] - [Classified Ads] - [Subscribe] - [Links] - [Books] - [Sponsors] -

Go Back   SmokStak > SmokStak® Vintage Electrical Equipment > Generators & Motors General Discussion > Onan Generators
Forgot Password? Join Us!

Notices

Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan 7.5 JB-3CR running issue


this thread has 173 replies and has been viewed 4888 times

Reply
 
Thread Tools Display Modes
  #1  
Old 03-16-2017, 04:29:50 PM
mheltunen mheltunen is offline
Registered-I
 
Join Date: Mar 2017
Location: Atlantic Mine, Michigan, USA
Posts: 85
Thanks: 56
Thanked 20 Times in 11 Posts
Default Onan 7.5 JB-3CR running issue

Hello everyone and here is my problem. I recently acquired a 7.5 JB. Owner had no idea if it ran or not. I was able to get the propane hooked up and got it to start but it immediately shuts down after firing. After some research I discovered that the points cover and the centrifugal switch is missing and the wires leading to it are cut. They did have a crude on/off switch wired in to bypass it but I removed it. I also discovered that that how they had wired the bypass had heated up and ruined the ignition coil as well. Does anyone have a source for these items? Sorry for the long post. Any help is appreciated. My email is mheltunen@yahoo.com

Thanks,
Attached Thumbnails
Click image for larger version

Name:	IMG_2333.jpg
Views:	86
Size:	149.9 KB
ID:	277657   Click image for larger version

Name:	IMG_2331.jpg
Views:	129
Size:	130.1 KB
ID:	277658   Click image for larger version

Name:	IMG_2330.jpg
Views:	119
Size:	114.3 KB
ID:	277659   Click image for larger version

Name:	IMG_2329.jpg
Views:	107
Size:	102.1 KB
ID:	277660  

Reply With Quote
Sponsored Links
  #2  
Old 03-16-2017, 04:43:26 PM
Billy J Shafer's Avatar
Billy J Shafer Billy J Shafer is online now
Subscriber
 
Join Date: Nov 2004
Location: Centerville, Texas
Posts: 16,236
Thanks: 8,265
Thanked 13,579 Times in 6,393 Posts
Default Re: 7.5 Onan JB-3CR running issue

Just give everyone time to show up. Some one will have the parts.
__________________
I don't talk to myself. This early in the morning. Why the hell should I talk to you.
Reply With Quote
The Following User Says Thank You to Billy J Shafer For This Post:
  #3  
Old 03-16-2017, 04:46:54 PM
Max Thompson Max Thompson is offline
Sponsor
 
Join Date: May 2009
Location: N.W. Missouri, USA
Posts: 5,717
Thanks: 4,952
Thanked 5,252 Times in 2,873 Posts
Default Re: 7.5 Onan JB-3CR running issue

I do not have either of the parts needed. There is a thread titled "Parting Out Thread" https://www.smokstak.com/forum/showt...=99191&page=14 below and that may be a good place to start with a parts need. Onan Parts is a sponsor here at The Stak and he may be able to help also. Otherwise flea-bay may be the next stop.

If you do not have a parts manual, you can find it here http://www.twinslan.net/~n0nas/manuals/onan/ #967-0223 should be the parts manual for your set. You also need the vibration isolators that go under the "feet" on your set.

You can safely run your set with a switch to bypass the centrifugal switch, some of the older sets had a "Hand Crank" switch that did about the same thing. You just need to be SURE to shut it off after the set starts.
Reply With Quote
The Following User Says Thank You to Max Thompson For This Post:
  #4  
Old 03-16-2017, 04:56:34 PM
mheltunen mheltunen is offline
Registered-I
 
Join Date: Mar 2017
Location: Atlantic Mine, Michigan, USA
Posts: 85
Thanks: 56
Thanked 20 Times in 11 Posts
Default Re: 7.5 Onan JB-3CR running issue

Max, do you know of a schematic/diagram to wire a bypass switch properly? And how my picture shows is all the parts I have, so no way to operate the plunger.

Thanks,
Reply With Quote
  #5  
Old 03-16-2017, 06:28:39 PM
Max Thompson Max Thompson is offline
Sponsor
 
Join Date: May 2009
Location: N.W. Missouri, USA
Posts: 5,717
Thanks: 4,952
Thanked 5,252 Times in 2,873 Posts
Default Re: 7.5 Onan JB-3CR running issue

What I am thinking is just wire the 2 wires that go to the centrifugal switch to a single pole single throw switch. The switch would be closed (on) to start the set, then turned off.

One of the smart guys (Leon, where are you) will be along and let you know if I am leading you astray.

In the JB / JC service manual #0967-0500 on page 82 you will find a diagram for the older spec. P set with a "hand crank" switch. I think this will allow you to start & run your set. The centrifugal switch is only "necessary " when remote starting the set.

If Yellowlister does not have cover for the points box, I think I have an extra somewhere.
Reply With Quote
The Following User Says Thank You to Max Thompson For This Post:
  #6  
Old 03-16-2017, 07:30:53 PM
Ray Lynch Ray Lynch is offline
Subscriber
 
Join Date: Aug 2014
Location: New Windsor, New York, USA
Posts: 430
Thanks: 304
Thanked 265 Times in 175 Posts
Default Re: 7.5 Onan JB-3CR running issue

Welcome to the Stak.
Make sure your cooling tins are all in place once you get the set up and running.
The set can overheat in a few minutes without the covers in place.
JB 's are nice sets. Good luck with it.
Ray
Try this vendor. He may have a centrifugal. switch as well.

http://m.ebay.com/itm/ONAN-JB-IGNITI...220?nav=SEARCH

Last edited by Ray Lynch; 03-16-2017 at 07:41:22 PM.
Reply With Quote
  #7  
Old 03-16-2017, 07:49:20 PM
len k len k is offline
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,530
Thanks: 382
Thanked 5,243 Times in 3,822 Posts
Default Re: 7.5 Onan JB-3CR running issue

Problem with manual switch bypassing the centrifugal switch is that applies power to coil all the time. If gen ran out of fuel power would still be applied to coil and it would eventually burn out again.

Want some type of auto shut down for coil power. Even if it was as simple as oil pressure switch driving a relay, so when oil pressure drops coil power stops.
Reply With Quote
  #8  
Old 03-16-2017, 07:57:22 PM
Dennis19508 Dennis19508 is offline
Registered-I
 
Join Date: Jan 2016
Location: Birdsboro, Pennsylvania
Posts: 57
Thanks: 51
Thanked 48 Times in 32 Posts
Default Re: 7.5 Onan JB-3CR running issue

Actually if you wire a switch in place of the centrifugal run switch it will need to be closed to run and turned off when stopped. This will be fine for testing but should not be left that way. That circuit is used for the LP gas valve and the ignition. If it is left on when the engine stalls, LP could leak. Plus the ignition coil will be energized if the points are closed and it would probably fry again.
Reply With Quote
  #9  
Old 03-16-2017, 08:53:57 PM
Leon N. Leon N. is offline
Registered-III
 
Join Date: Oct 2009
Location: N. Chelmsford, MA, USA
Posts: 3,426
Thanks: 634
Thanked 1,959 Times in 1,174 Posts
Default Re: 7.5 Onan JB-3CR running issue

Max I agree with your thinking in post #5. However, not knowing what this specific JB was built too, I would suggest someone provide the factory build sheet to see if the actual control wiring diagram can be identified.

Another side point about that hand-crank feature. If someone is going to hand crank the JB to start it, the physical exertion required to start the JB is practically impossible unless one is either using gasoline or the Garrestson has a primer button.I have no primer button, and I could never hand crank sufficiently to start it when using NG.

On the other hand ( no pun intended) I have used the hand crank to start the JB when the 12 volt battery was discharged, that is could only spin the JB for 1 or 2 seconds OR when the ignition start relay was not working.
Reply With Quote
The Following User Says Thank You to Leon N. For This Post:
  #10  
Old 03-16-2017, 09:09:38 PM
len k len k is offline
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,530
Thanks: 382
Thanked 5,243 Times in 3,822 Posts
Default Re: 7.5 Onan JB-3CR running issue

Agree hand crank might be OK with a semi dead bat helping.
Were all getting older, few winters ago my back didn't like pull starting just a 7 hp snowblower that had issues.
JB is ~980 CC engine, ouch.

Last edited by len k; 03-17-2017 at 12:46:46 PM.
Reply With Quote
  #11  
Old 03-16-2017, 10:58:21 PM
David C David C is offline
Registered-III
 
Join Date: Mar 2006
Location: Lake Jackson,Texas
Posts: 1,335
Thanks: 951
Thanked 822 Times in 540 Posts
Default Re: 7.5 Onan JB-3CR running issue

If you just want to get it running, you can just run a hot wire from an on/off switch through the oil pressure switch (as long as it is normally open) then to the ignition coil (and resistor if coil requires on) and then to the points. Get a HD push button switch and run a wire to the "S" terminal on the starter solenoid for the start circuit. A very basic electrical system, but it does eliminate the capability of remote start. I know most of the guys here cringe when I mention this type of wiring, but it does allow you to use the generator until the time comes that you have rounded up all of the parts to return it to the original Onan design.

David C.
Reply With Quote
  #12  
Old 03-16-2017, 11:22:34 PM
yellowlister yellowlister is offline
Subscriber
 
Join Date: Feb 2010
Location: Granada Hills, California
Posts: 3,907
Thanks: 1,798
Thanked 1,922 Times in 1,258 Posts
Default Re: 7.5 Onan JB-3CR running issue

Pretty sure I have a centrifugal switch and may have the cover..
Reply With Quote
The Following 2 Users Say Thank You to yellowlister For This Post:
  #13  
Old 03-16-2017, 11:46:28 PM
mheltunen mheltunen is offline
Registered-I
 
Join Date: Mar 2017
Location: Atlantic Mine, Michigan, USA
Posts: 85
Thanks: 56
Thanked 20 Times in 11 Posts
Default Re: 7.5 Onan JB-3CR running issue

Thanks guys, I sure appreciate all of the feedback.
Reply With Quote
  #14  
Old 03-17-2017, 09:20:53 AM
mheltunen mheltunen is offline
Registered-I
 
Join Date: Mar 2017
Location: Atlantic Mine, Michigan, USA
Posts: 85
Thanks: 56
Thanked 20 Times in 11 Posts
Default Re: 7.5 Onan JB-3CR running issue

Will any 6V duel plug wire coil work for this unit? The onan coil is pricey and considering we have $250 into it now we are unsure what the budget for repairs will be. When it initially fired it ran for a few seconds before shutting down. What caused the ignition to lose power? and does anyone have an ignition schematic for this model. I'm not even sure what year the generator is. Can this be determined by the plate on the side of the cover? I do have the cover for the "Fan" side, but the cover over the carburetor and exhaust manifold is missing. can it be safely run without those without overheating?

I sure appreciate all of everyone's help.

Thanks!

---------- Post added at 09:20:53 AM ---------- Previous post was at 08:59:51 AM ----------

I should point out that when it fired it was using a coil off of an old miller welder with an onan engine. Spark was pretty weak though. Points were gapped to .020
Reply With Quote
  #15  
Old 03-17-2017, 09:40:43 AM
Ray Lynch Ray Lynch is offline
Subscriber
 
Join Date: Aug 2014
Location: New Windsor, New York, USA
Posts: 430
Thanks: 304
Thanked 265 Times in 175 Posts
Default Re: 7.5 Onan JB-3CR running issue

Built March 1977
It will overheat if the tins are not installed.
Ray
Reply With Quote
  #16  
Old 03-17-2017, 09:47:23 AM
Kevin K Kevin K is offline
Registered-III
 
Join Date: Jan 2005
Location: upstate New York USA
Posts: 3,479
Thanks: 3,112
Thanked 3,441 Times in 1,875 Posts
Default Re: 7.5 Onan JB-3CR running issue

Quote:
Originally Posted by mheltunen View Post
Will any 6V duel plug wire coil work for this unit? The onan coil is pricey and considering we have $250 into it now we are unsure what the budget for repairs will be.
That should work fine. If you eliminate the 1.72 ohm ignition resistor, you should be able to use a 12 volt dual tower coil.

The age of your Onan is in the serial number. March (C) 1977 (77).

I found the production order for your generator. The wiring diagram number was difficult to read, but it looks like 612-4794.
Attached Files
File Type: pdf 75JB3CR12424AA.pdf (24.1 KB, 14 views)
File Type: pdf 612-4794.pdf (158.8 KB, 20 views)
Reply With Quote
The Following 2 Users Say Thank You to Kevin K For This Post:
  #17  
Old 03-17-2017, 09:54:29 AM
Leon N. Leon N. is offline
Registered-III
 
Join Date: Oct 2009
Location: N. Chelmsford, MA, USA
Posts: 3,426
Thanks: 634
Thanked 1,959 Times in 1,174 Posts
Default Re: 7.5 Onan JB-3CR running issue

Mr. Heltunen: To answer some of your questions, such as finding the correct wiring diagram for your JB, we need one of the stack members to produce the factory build sheet for this particular machine. Also, what are your intentions or plans for this JB?

Yes, one can in some cases substitute non Onan parts and modify the wiring, etc, but looking at your pictures, this puppy need lots of attention and restoration of missing parts to return this machine to a reliably operating unit.

To answer some of your other questions, this JB was built in March of 1977. What caused the ignition to lose power?, Hmmm, hard to say since it appears the unit was modified and we do not know exactly what you have here. Yes, you do need the cover for the carburetor side and all the sheet metal enclosures to operate and provide adequate cooling.
Reply With Quote
The Following User Says Thank You to Leon N. For This Post:
  #18  
Old 03-17-2017, 10:00:16 AM
mheltunen mheltunen is offline
Registered-I
 
Join Date: Mar 2017
Location: Atlantic Mine, Michigan, USA
Posts: 85
Thanks: 56
Thanked 20 Times in 11 Posts
Default Re: 7.5 Onan JB-3CR running issue

Our intentions for this unit was to provide power to a remote hunting cabin. I don't have any interest in a restoration just looking for a reliable and cost effective power source. I have a strong dislike for cheap Chinese gensets. Onans when properly maintained have always seemed like excellent units.
Reply With Quote
The Following User Says Thank You to mheltunen For This Post:
  #19  
Old 03-17-2017, 12:52:01 PM
len k len k is offline
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 14,530
Thanks: 382
Thanked 5,243 Times in 3,822 Posts
Default Re: 7.5 Onan JB-3CR running issue

Can use modern 2 tower coils ( waste spark). Might need a resistor in series with primary if coil ohms are too low.

Here's some alternate ideas for using modern ignition moduals and coils

https://www.smokstak.com/forum/showthread.php?t=167037
Reply With Quote
  #20  
Old 03-17-2017, 03:19:57 PM
mheltunen mheltunen is offline
Registered-I
 
Join Date: Mar 2017
Location: Atlantic Mine, Michigan, USA
Posts: 85
Thanks: 56
Thanked 20 Times in 11 Posts
Default Re: 7.5 Onan JB-3CR running issue

Perhaps someone can clarify this for me as well. the coil on my model is a 6 volt 166C346. So i am assuming it is supposed to have a resistor on the wire feeding the positive side of this coil. Looking on my set I have been unable to locate one. There is a resistor on the negative side feeding the point. According to drawing 612-4794 the coil is fed from position #4 on terminal block 12. tracing it down on the drawing I see no indications of a resistor as well. I am not an electrician but usually I'm able to head scratch my way thru a schematic. The wires feeding centrifugal switch (wires #5 on TB12 and wire from B+ on tb11 have been cut and are hanging loose.

---------- Post added at 03:19:57 PM ---------- Previous post was at 03:17:13 PM ----------

I have also taken the time to remove any wiring modifications that were done and using the schematic I returned the wiring to their factory locations.
Reply With Quote
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

F o r u m Jump

Similar Threads Chosen at Random
Thread Thread Starter F o r u m Replies Last Post
Onan KY Microlite 4000 Running Issue bills02jeep Onan Generators 14 12-10-2016 12:32:44 PM
small associated running issue (help!) Chris Steffen Antique Gas Engine Discussion 8 12-25-2012 01:57:23 PM
Onan Model 4.0 DKC-3CR/1A Serial # E860820953 Running issue KWA915 Onan Generators 1 07-02-2012 10:29:47 PM
Maytag 92 running issue Lvolling Maytag Engine Collectibles 3 05-29-2011 01:34:09 AM
Onan DJC12 start/run, stay running issue dougvnbalto Onan Generators 2 10-29-2010 08:59:03 PM


Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 02:48:59 PM.

Smokstak and Enginads site search!


All use is subject to our TERMS OF SERVICE
SMOKSTAK® is a Registered Trade Mark - A Community of Antique Engine Enthusiasts
Copyright © 2000 - 2016 by Harry Matthews P.O. Box 5612 - Sarasota, FL 34277