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

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

Notices

Onan Generators Restoring, operating and maintaining vintage Onan generators.

Onan Generators

Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L


this thread has 39 replies and has been viewed 1165 times

Reply
 
Thread Tools Display Modes
  #1  
Old 02-07-2018, 11:45:28 AM
maineboy maineboy is offline
Registered
 
Join Date: Oct 2010
Location: cornwall VT
Posts: 11
Thanks: 12
Thanked 2 Times in 1 Post
Default Onan JC - Problem With My “Very Reliable” 15JC-3R/3998L

Problem with my “very reliable” 15JC-3R/3998L
I was wonder if I could pose a question or two to the great minds of the Onan Forum.
As stated in the title I have a 15JC-3R/3998L ser # 55C828097 - in-line 4 with about 3000 hours on it.
15KW - 62.5 amps - 120/240 volts - 60 cycles - 1 phase - 1800 RPM
It was converted to LP about 20 years ago with a Garretson LP conversion kit.
It is piped to a LP tank- at the machine it has an inline solenoid which is energized at start-up and has a KN regulator.
This machine has been purring like a kitten for the past 6 years. I cycle / run / exercise it about once a month to keep it in shape and I use it whenever we lose power from the grid (probably about 20-30 hours annually).
Problem-
Last week when I was exercising the machine, it stalled after 5 minutes of running (which it has never done). I started it again and it ran for a few minutes and then stalled again. Then it would not start, it would run on what sounded like a couple of cylinders and it would kind of “diesel” for a few seconds and quit. It seemed fuel starved, or it seemed to be out of time.
I checked the LP fuel supply and the electric in line solenoid and everything was functioning properly. The diaphragm on the KN regulator looked stretched out so I ordered and new KN reg and installed it, I would have bet my last dollar that it was a fuel issue. It does not appear to be a fuel issue.
Interesting point - I tried to start it probably 6-8 times ( 10 second cranks) strong battery, good fuel flow, good spark. On the last try it back-fired a few times and then one really big back fire, which was more like a bottom end (crankcase backfire) which blasted the dip stick across the room and blew the crankcase breather off.
Do you think it is possible that the distributor gear skipped and is now out of time?
Is it possible that the timing chain jumped?
I’m going to try and check to see if the valves are closed on cylinder 1 at TDC and if the distributor button is in the right position to send spark to cylinder 1.

Any insight or things to check would be greatly appreciated.
All the best,
Jason
Attached Thumbnails
Click image for larger version

Name:	onan.jpg
Views:	91
Size:	178.0 KB
ID:	302548  
Reply With Quote
Sponsored Links
  #2  
Old 02-07-2018, 11:55:22 AM
Billy J Shafer's Avatar
Billy J Shafer Billy J Shafer is offline
Subscriber
 
Join Date: Nov 2004
Location: Centerville, Texas
Posts: 16,573
Thanks: 8,517
Thanked 13,943 Times in 6,555 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

It has no timing chain. It is gear to gear. Timing could be off or a valve problem. I would also make sure the vents on the fuel system are clear. Also check over the ignition system.
__________________
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 02-07-2018, 12:28:53 PM
EnginePat EnginePat is offline
Subscriber
 
Join Date: Aug 2011
Location: Connecticut
Posts: 588
Thanks: 343
Thanked 166 Times in 119 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

Points and condensor would be one place to look.
__________________
Pat
5GO 3/RA
7.5 jb's x3
Reply With Quote
The Following User Says Thank You to EnginePat For This Post:
  #4  
Old 02-07-2018, 12:30:13 PM
Kevin K Kevin K is offline
Registered-III
 
Join Date: Jan 2005
Location: upstate New York USA
Posts: 3,641
Thanks: 3,345
Thanked 3,732 Times in 1,992 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

Did you check the propane supply by connecting a manometer to the Garretson input test port to verify you have 11"WC propane pressure with the engine running?
Reply With Quote
  #5  
Old 02-07-2018, 12:51:29 PM
JohnnyC JohnnyC is offline
Subscriber
 
Join Date: Jun 2014
Location: Boonton, New Jersey
Posts: 4,330
Thanks: 1,364
Thanked 2,058 Times in 1,217 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

Blew the dipstick out as well as the breather?? Do a compression test on all cylinders to start with.

JohnnyC
New Jersey
Reply With Quote
The Following 3 Users Say Thank You to JohnnyC For This Post:
  #6  
Old 02-07-2018, 01:21:07 PM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 15,465
Thanks: 412
Thanked 5,571 Times in 4,044 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

Agreed!!!!

Blew the dipstick out as well as the breather?

Unless propane somehow leaking into crankcase, I'm thinking hole in piston letting propane into crankcase, then igniting and pressure blowing out the dip stick
Reply With Quote
The Following User Says Thank You to len k For This Post:
  #7  
Old 02-07-2018, 01:23:23 PM
Leon N. Leon N. is offline
Registered-III
 
Join Date: Oct 2009
Location: N. Chelmsford, MA, USA
Posts: 3,715
Thanks: 671
Thanked 2,130 Times in 1,279 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

Interesting! Blew the dip stick out! I would suspect somehow propane is getting into your crankcase. How could that occur? Via the carburetor cc breather or a malfunctioning KN regulator or a combustion chamber malfunction. I suspect when the JC backfired it set off the combustible mixture in the cc. Maybe your gas regulator is not properly set?

Can you explain what you meant bu a stretched diaphgram? I have a KN regulator which is now some 48 years old and the only problem I had with it was a plugged vent screen.
Reply With Quote
  #8  
Old 02-07-2018, 02:03:03 PM
BigBlockChev's Avatar
BigBlockChev BigBlockChev is offline
Subscriber
 
Join Date: Jan 2007
Location: Coquitlam, BC, Canada
Posts: 1,952
Thanks: 350
Thanked 1,504 Times in 883 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

I have seen propane engines leak a considerable amount of propane into the oil sump then backfire as described . Back to basics , check the fuel pressure with a manometer to make sure it is correct and not getting too much fuel which can cause ignition failure. Propane has a narrow % range of limits of combustion too much and it won’t burn same as too little. Cheers Dan
__________________
It's always something simple.
One test is worth a thousand guesses.
If some is good and more is better then too much is just enough
Reply With Quote
The Following User Says Thank You to BigBlockChev For This Post:
  #9  
Old 02-07-2018, 02:18:18 PM
len k len k is online now
Registered-III
 
Join Date: Jun 2012
Location: Manchester, New Hampshire
Posts: 15,465
Thanks: 412
Thanked 5,571 Times in 4,044 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

Since you have a magnaciter I'ld disconnect the magnaciter from 120V lines untill you get engine running properly. Low rpm (low hz) can smoke the magnaciter coils.
Reply With Quote
The Following User Says Thank You to len k For This Post:
  #10  
Old 02-07-2018, 02:23:40 PM
Motorhead's Avatar
Motorhead Motorhead is offline
Subscriber
 
Join Date: May 2007
Location: Central Coast, California
Posts: 3,580
Thanks: 1,648
Thanked 2,434 Times in 1,284 Posts
Default Re: Onan JC - Problem with my “very reliable” 15JC-3R/3998L

On the Garrettson regulator, there is a small VENT that is on the outside edge of the regulator. It is a brass fitting with a small screen pressed into it. Check it to make sure it doesn't have an obstruction.
I would also check your point gap on the distributor points. The distributor cam can get dry and wear the point rub block down enough to close your point gap.
LET US KNOW WHAT YOU FIND.
__________________
Back of 1958 5CCK
Contractors model
On trailer owned by
"Ma" Bell.
Reply With Quote
The Following 2 Users Say Thank You to Motorhead For This Post:
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
Emerson Btantingham Gasoline Engine Type “N” 4.H.P TractorDom Antique Gas Engine Discussion 0 11-20-2015 10:13:08 PM
Problem with Onan 15JC Kpack Onan Generators 9 10-31-2012 01:23:24 PM
“The Schuchardt’s Last Car Show” Auction September 15, 2012 Craig A Antique Autos and Trucks 4 09-15-2012 09:30:43 PM
Solenoid for a 15JC-3R/3998L maineboy Onan Generators 12 11-11-2010 02:21:29 PM


Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 05:39:55 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