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

Engine ran without cover on Onan 15JC


this thread has 24 replies and has been viewed 823 times

Reply
 
Thread Tools Display Modes
  #11  
Old 03-18-2017, 01:59:28 PM
Kevin K Kevin K is offline
Registered-III
 
Join Date: Jan 2005
Location: upstate New York USA
Posts: 3,772
Thanks: 3,457
Thanked 3,876 Times in 2,064 Posts
Default Re: Engine ran without cover on Onan 15JC

How much speed did it drop? I know it is difficult to estimate, but did it sound like the engine was lugging down? Was it really 4 minutes, or a lot longer? When cranking to restart it, did it seem like it was cranking slowly?

If you have a bore scope, check the cylinders with it. You could try cranking it by hand with the spark plugs removed to check for any additional drag. A compression test is in order, and a leak down test as well.

I would not tear it down just yet. An oil change would be a good idea,.

It was started from cold (30 degrees) and ran four minutes with no load. Even with the cover missing it would have had some cooling. I'm not sure it would overheat in four minutes under those conditions.

Could it be the engine speed change you thought you heard was really a change in engine sound as the choke came off and the mixture changed?
Reply With Quote
The Following 2 Users Say Thank You to Kevin K For This Post:
Sponsored Links
  #12  
Old 03-18-2017, 02:08:58 PM
beezerbill beezerbill is offline
Subscriber
 
Join Date: Sep 2012
Location: Boulder, Colorado
Posts: 1,151
Thanks: 180
Thanked 622 Times in 415 Posts
Default Re: Engine ran without cover on Onan 15JC

Your idea of a borescope is a good one. Do as others recommend - change the oil and filter. You could go as far as examining the oil that came out for debris or aluminum flakes (start with a clean drain pan) and peel the old filter apart and look for debris in it. With fresh oil and filter, run it for an hour or more under a pretty good load and listen for any new noises, particularly piston slap. Then drain the oil again and look for any debris that might come from a piston that started to seize and is wearing back in. Also look for oiling on the spark plug. And don't worry about it too much. Years ago when I was building performance British motorcycles I would occasionally have one try to seize right after rebuild, would back off on it for a bit, and it would be just fine after that. This was back when I had the belief that the best way to break in an engine is to run it hard right from the start. I've even pulled a few apart that went many trouble-free miles, only to discover light seize marks on the pistons.
Reply With Quote
  #13  
Old 03-18-2017, 03:32:16 PM
bowser22 bowser22 is offline
Registered
 
Join Date: Oct 2016
Location: Bras d'Or Lake, Nova Scotia, Canada
Posts: 22
Thanks: 7
Thanked 1 Time in 1 Post
Default Re: Engine ran without cover on Onan 15JC

It only dropped a couple hundred rpm, then I thought hmm thats weird. It was still even within range on the frequency meter. It wasn't lugging or anything. Then I reinstalled the cover and started it, started normal, not labored. It was really only about 4 minutes.
Reply With Quote
  #14  
Old 03-18-2017, 04:27:10 PM
Max Thompson Max Thompson is offline
Sponsor
 
Join Date: May 2009
Location: N.W. Missouri, USA
Posts: 5,923
Thanks: 5,212
Thanked 5,606 Times in 3,006 Posts
Default Re: Engine ran without cover on Onan 15JC

I will take a chance and try a different thought.

If this is a gasoline set, maybe the choke just finished opening up all the way and made the engine sound different. At 30 degrees for 4 minutes with no load, damage is very unlikely. Or maybe as the cover was falling off, it caught the throttle linkage and pulled it down a little.

It can not hurt anything to change the oil and filter and keep an eye on it for an extended loaded run. But at 30 degrees the shutters on my JC will not open for at least 10 - 15 minutes.
Reply With Quote
The Following 3 Users Say Thank You to Max Thompson For This Post:
  #15  
Old 03-18-2017, 04:31:30 PM
Wayne 440 Wayne 440 is online now
Registered-III
 
Join Date: Nov 2004
Location: Kentucky
Posts: 5,881
Thanks: 357
Thanked 4,949 Times in 2,378 Posts
Default Re: Engine ran without cover on Onan 15JC

Quote:
Originally Posted by Max Thompson View Post
...maybe as the cover was falling off, it caught the throttle linkage and pulled it down a little...
Good possibility.

Quote:
...It can not hurt anything to change the oil and filter and keep an eye on it for an extended loaded run...
That was my thinking, oil and a filter is cheap compared to most engine work.
Reply With Quote
  #16  
Old 03-18-2017, 04:44:42 PM
Billy J Shafer's Avatar
Billy J Shafer Billy J Shafer is online now
Subscriber
 
Join Date: Nov 2004
Location: Centerville, Texas
Posts: 16,899
Thanks: 8,724
Thanked 14,258 Times in 6,729 Posts
Default Re: Engine ran without cover on Onan 15JC

I think you may have just been hearing things. I have gone to JCs to work on them. To find the cooling door off and on the floor. I have a hard time believing a short time in that temp. Doing any damage. They can ice up in the carb,if conditions are just right. Ice breaks off and effects the running. Choke delay on opening can also cause a problem. I wouldn't worry about.
__________________
I don't talk to myself. This early in the morning. Why the hell should I talk to you.
Reply With Quote
The Following 2 Users Say Thank You to Billy J Shafer For This Post:
  #17  
Old 03-18-2017, 05:49:09 PM
Gunny Gunny is offline
Subscriber
 
Join Date: Feb 2005
Location: North Carolina
Posts: 3,695
Thanks: 1,567
Thanked 1,585 Times in 1,008 Posts
Default Re: Engine ran without cover on Onan 15JC

Going to agree with Billy on this. As it was not under load, doubt it was hot enough t do any damage, especially in under 5 minutes. I've seen them run for 20 minutes with the cover off for weeks at a time for exercise with no apparent damage.

Think all is good.
Reply With Quote
The Following 2 Users Say Thank You to Gunny For This Post:
  #18  
Old 03-18-2017, 06:09:42 PM
geezer88 geezer88 is offline
Registered-I
 
Join Date: Dec 2014
Location: Corvallis, Oregon
Posts: 219
Thanks: 40
Thanked 154 Times in 74 Posts
Default Re: Engine ran without cover on Onan 15JC

I'll go with Billy and Gunny on this one. Without the covers on, you've got a motorcycle engine. From a cold start, no load, four minutes wouldn't seem that bad. I bet it's fine.

tom
Reply With Quote
  #19  
Old 03-18-2017, 06:42:56 PM
Troll's Avatar
Troll Troll is offline
Subscriber
 
Join Date: Jan 2017
Location: Farmington, Illinois
Posts: 869
Thanks: 22
Thanked 513 Times in 267 Posts
Default Re: Engine ran without cover on Onan 15JC

I think it's junk and to alleviate your pain should be put on a truck headed my way in an expeditious manner.....

I don't need to repeat good advice but don't think there is anything to worry about. I'm willing to take the chance and make use of it however.....
Reply With Quote
  #20  
Old 03-18-2017, 07:11:30 PM
Mike57 Mike57 is offline
Subscriber
 
Join Date: Sep 2013
Location: Sunnyvale, Texas, USA
Posts: 169
Thanks: 120
Thanked 92 Times in 60 Posts
Default Re: Engine ran without cover on Onan 15JC

I have several indicator gauges on my JC, including CHT and EGT. I've run mine without covers up to 5 minutes, at a lot higher ambient(80) than what you were at. It took 5 minutes for the CHT to hit 325 and I shut it down. If you were truly only at 4 minutes, you're probably fine.
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 15JC air cooled engine timing cjgpokny Onan Generators 15 05-02-2014 08:21:14 AM
Help me out with an Onan 15JC wilson Ross Onan Generators 21 08-29-2012 12:00:29 PM
Onan 15JC Stuck engine ?? John10 Onan Generators 2 10-25-2009 06:50:44 PM
Possible frozen Onan engine on a 15JC Gen Set John10 Onan Generators 4 10-03-2009 03:29:30 PM
15JC top cover crbearden Onan Generators 2 12-28-2007 05:07:37 PM


Use "Ctrl" mouse wheel to change screen size.
All times are GMT -4. The time now is 07:00:19 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