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Onan twin running on one cylinder. I'm stumped...

Started by Kbeitz, July 07, 2017, 12:33:28 PM

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Kbeitz

My air cleaner filter would need to have a hole in it for a mouse or rag to get past it.
But you are right it seem like one side is not getting any gas.
Collector and builder of many things.
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Jeff

You need to confirm that air fuel can get down that side. Mice and bees can get in a hole not much bigger that a pencil eraser.
Just call me the midget doctor.
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Commercial circle sawmill sawyer in a past life for 25yrs.
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Kbeitz

I bought another compression checker. This new one I got says I got 100 psi on the running side
and 95 psi on the non-running side. So just for the heck of it I took the top of the engine off and
backed off the tappets on the non-running side one turn. Now it will run on both side at full throttle
but nothing lower. I'm busy tomorrow but Tuesday I'm going to back off the tappets another turn
and see what happens. They are suposta be set at IN: 0.005" and EX: 0.013"  but that's not working.
I'm still puzzled. I drove it around for about 30min to see if it would change. Nope...
Collector and builder of many things.
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slider

Kebitz this may not help but i had a similar problem with a 24 hp onan and it was trash in the main jet.Under load it would stumble and seamed to be running on one cylinder.Jeff is right about the coils the oem coils were not cheap.
al glenn

Kbeitz

I have tried different coils and I switches the wires from one side of the coil to the other with no difference.
I'm going to pull an intake and car off another engine and try that.
Collector and builder of many things.
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whitepine2

  Did you ever find out what was going on with your one cylinder firing?     

Ljohnsaw

Also waiting for a solution.  I had a mouse family move in to my air box on my Grizzly 550 - what a mess...

Unrelated but interesting (to me).  I have a 16hp Wisconsin on my trencher.  Was running great last year and earlier this spring but just couldn't get it to start a few weeks ago.  No spark.  I had put in new points and coil along with a new carb last year.  I opened up the points cover (could not see into it with the engine installed in the trencher).  I scraped a knife through the contacts (corrosion?) and now it runs great again.  I did not feel any roughness when scraping, though.
John Sawicky

Just North-East of Sacramento...

SkyTrak 9038, Ford 545D FEL, Davis Little Monster backhoe, Case 16+4 Trencher, Home Built 42" capacity/36" cut Bandmill up to 54' long - using it all to build a timber frame cabin.

Kbeitz

No... It's sitting in line to be worked on. I have other onan engines for parts.
I guess I got to do the shade tree mechanic thing and start swapping parts
and see what works. First thing I'm trying is to switch the intake and carb.
The tractor is in very good condition so I don't want to give up on her.
This has been a very busy year for me. After I finish my edger I have a can
conveyor I need to build for the junkyard so I will be awhile until I can get
to the tractor, but I will keep you all posted. Thanks for your interest.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
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Ox

I'm also waiting.  I've never heard of such a thing and want to see what caused this problem.

What is a can conveyor?

I don't know how this will matter, but a backfire can sometimes half shear the key off holding the flywheel which can throw the timing off.  But since the other cylinder is firing this don't make any sense.  Just figured I'd throw it out there to maybe spark a thought or something.

It may be a slightly bent valve stem or something like that.  I've seen the ethanol fuel actually stick valves in the guide and then they bend.  This happened after sitting over the winter mostly I think.



K.I.S.S. - Keep It Simple Stupid
Use it up, wear it out, make it do or do without
1989 GMC 3500 4x4 diesel dump and plow truck, 1964 Oliver 1600 Industrial with Parsons loader and backhoe, 1986 Zetor 5211, Cat's Claw sharpener, single tooth setter, homemade Linn Lumber 1900 style mill, old tools

coxy

I'm sticking to what I said before of it being a week cylinder and the hotter it gets the less compression it has to fire  :)

Ox

K.I.S.S. - Keep It Simple Stupid
Use it up, wear it out, make it do or do without
1989 GMC 3500 4x4 diesel dump and plow truck, 1964 Oliver 1600 Industrial with Parsons loader and backhoe, 1986 Zetor 5211, Cat's Claw sharpener, single tooth setter, homemade Linn Lumber 1900 style mill, old tools

Kbeitz

Quote from: coxy on August 27, 2017, 11:10:06 AM
I'm sticking to what I said before of it being a week cylinder and the hotter it gets the less compression it has to fire  :)

Every time I check it it has at least 100 psi or more.
Is that not enough?
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Kbeitz

Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

hamish

Quote from: Kbeitz on August 28, 2017, 07:36:51 PM
Google say an engine will run as low as 45psi

https://www.lawnsite.com/threads/compression-test-for-small-engines.72249/

A four stroke engine will not run with a mere 45psi of compression, regardless of what Mr Google says.
Even engines with an automatic compression release when run in there normal orientation will not run with 45 PSI Compression.
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DelawhereJoe

I've got an old b&s 3.5 hp push mower with so much blow by from the rings that it will choke itself out if the breather line is hooked to the carb. It will however start on the 1st or 2nd pull after sitting all winter sith the same old gas in it. I've been waiting for the thing to die for the past 8 years but it keeps on starting every time.
WD-40, DUCT TAPE, 024, 026, 362c-m, 041, homelite xl, JD 2510

coxy

Quote from: Kbeitz on August 28, 2017, 07:32:04 PM
Quote from: coxy on August 27, 2017, 11:10:06 AM
I'm sticking to what I said before of it being a week cylinder and the hotter it gets the less compression it has to fire  :)

Every time I check it it has at least 100 psi or more.
Is that not enough?
are you checking it after its hot  the Honda motor I had tested good till you run it for a half hour or more at full throttle then would loose compression on one side and run like crap  I'm not saying that's whats wrong with yours

Kbeitz

Quote from: hamish on August 28, 2017, 07:56:59 PM
Quote from: Kbeitz on August 28, 2017, 07:36:51 PM
Google say an engine will run as low as 45psi

https://www.lawnsite.com/threads/compression-test-for-small-engines.72249/

A four stroke engine will not run with a mere 45psi of compression, regardless of what Mr Google says.
Even engines with an automatic compression release when run in there normal orientation will not run with 45 PSI Compression.

I found more links that say you can make an engine run with 30 psi.
Others say above 75 pounds then the engine has enough compression to run.

I know my old Hit&Miss engines are very low compression engines.

But from everything I read I think my 100 psi should be running.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

starmac

Probably is not your problem, but I have several times had new plugs that would throw a pretty spark, but not fire a lick under compression, this has usually been with ngk plugs, but seen the same thing with other brands too.

9 times out of 10, I could pull the plug and spray it with WD40 and it would crank at least once. I do not know the compression the onan should put out, but it should at least hit on 100.
Old LT40HD, old log truck, old MM forklift, and several huskies.

martyinmi

Just for giggles, back off your intake lash to .020" and exhaust to .030".
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Know God, Know Peace!

Kbeitz

Quote from: martyinmi on September 10, 2017, 06:49:15 AM
Just for giggles, back off your intake lash to .020" and exhaust to .030".

Thanks... I will try that...
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Kbeitz

Well I put a few more hours working on it and still nothing.
I changed out the carb and intake. It made no difference at all.



 



 



 
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Andries

My LT30 has a 24 hp Onan, which had the same problems that you describe.
After a whole lot of head scratching, it came back to reply #19.
Replaced the old coil with aproven and new coil.
That was five years ago.
She runs like a champ now.
LT40G25
Ford 545D loader
Stihl chainsaws

Kbeitz

Quote from: Andries on September 17, 2017, 06:56:26 PM
My LT30 has a 24 hp Onan, which had the same problems that you describe.
After a whole lot of head scratching, it came back to reply #19.
Replaced the old coil with aproven and new coil.
That was five years ago.
She runs like a champ now.

Tomorrow I will swap a coil off one of my other running tractor and report back.

Thanks for all the ideas..
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

coxy


elitts

If you don't end up finding a solution, I would suggest taking your question to mytractorforum and asking it under the "Lawn & Garden Tractor"/Gravely forum.  The old 1970-1990 Gravely tractors frequently used Onan 16hp & 18hp engines and there are a couple of guys there who really REALLY love Onan engines and have spent decades restoring them.

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