iDRY Vacuum Kilns

Sponsors:

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

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

Previous topic - Next topic

0 Members and 2 Guests are viewing this topic.

Kbeitz

Quote from: elitts on September 19, 2017, 08:56:33 AM
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.

Thanks... I'm a member there. I love that forum until they changed everything.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

starmac

If there is no vacuum leak and the dead cylinder has compression and is getting gas, it sure seems like the coil should be the culprit, but then again switching the plug wire should have changed the dead cylinder too. So far this is a head scratcher.
Old LT40HD, old log truck, old MM forklift, and several huskies.

Kbeitz

Quote from: starmac on September 20, 2017, 11:43:05 PM
If there is no vacuum leak and the dead cylinder has compression and is getting gas, it sure seems like the coil should be the culprit, but then again switching the plug wire should have changed the dead cylinder too. So far this is a head scratcher.

Sorry I just did not get time yet to try a third coil change.

I had the same thoughts as above. But then I remembered that
even though I swapped the wires in the coil and tried new wires
the wire going to the front cly that's not working is around  6-8"
longer that the one that's working. It shows a real good spark
when the plugs out but things change when under compression.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

starmac

Well I will be the first to admit that I have not seen everything (or even close to it). I have seen plugs that fired good when grounded, but not under compression several times, but never a coil. I do not see how compression could possibly affect the spark coming from the coil.

If the plug wire on the affected cylinder is longer, then you probably changed the wires at the coil itself, which makes me wonder if their might not be too much resistance in the wire itself.
Old LT40HD, old log truck, old MM forklift, and several huskies.

Al_Smith

Just for general info those Onan coils on some models are a double coil like a Harley .Both plugs fire at the same time .

Kbeitz

All coil wires that I changed came off other Onans engines.

Yes this has a double coil just like a Harley.

It's called a wasted spark system.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

Hilltop366

Kind of sounds like a intake vacuum leak or valve problem to me.

If it was a no spark issue I would think the spark plug on the dead cylinder would be wet after running.

Kbeitz

Quote from: Hilltop366 on September 21, 2017, 11:46:00 AM
Kind of sounds like a intake vacuum leak or valve problem to me.

If it was a no spark issue I would think the spark plug on the dead cylinder would be wet after running.

Changed the intake twice and it has a little over 100psi on the no running side.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

coxy

are you checking it after it has run for a little while and getting a 100

Magicman

Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

pineywoods

I don't think them onans had hydraulic lifters, if so, maybe collapsed lifter ? Way back in the dim dark past, seems I remember getting bit by a similar problem on a briggs. One lobe on the camshaft was completely worn off, intake valve never opened...
1995 Wood Mizer LT 40, Liquid cooled kawasaki,homebuilt hydraulics. Homebuilt solar dry kiln.  Woodmaster 718 planner, Kubota M4700 with homemade forks and winch, stihl  028, 029, Ms390
100k bd ft club.Charter member of The Grumpy old Men

Magicman

I was not considering hydraulic lifters but even so, whether the valves were lifting and at the proper time.
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

sawguy21

If that were the case neither side would run. Did you have the valves out and check for a loose seat?
old age and treachery will always overcome youth and enthusiasm

Magicman

Yup, you are correct regarding the timing.  Kb has made compression test which are OK, the spark is OK, carburetor is OK, so the only thing left is the gas mixture is not getting into the cylinder, or the exhaust is never leaving. 
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

Al_Smith

It doesn't make any sense it would fire one side of the coil and not the other .Assuming it's a battery spark which frankly is all I've
ever seen on that engine it only has a set of points and condenser plus the double coil .
Actually on that "wasted spark " it isn't really wasted .By firing every time the piston is near top dead center it has a tendency to keep the plug clean .

The only thing I can think off would be the coil halves  being wired in series which I doubt would be the case .Perhaps a weak condenser with the first coil in line robbing all the voltage but that is highly unlikely .
Rambling on I once had a mag coil go funky on an Eisenman mag on a D4 Cat pony engine .Temporarily to get it running I used the mag points and two car coils and a 6 volt dry cell lantern battery .If you collect junk some times you have to get rather ingenious . :D

Ljohnsaw

Quote from: Magicman on September 22, 2017, 08:36:30 AM
Yup, you are correct regarding the timing.  Kb has made compression test which are OK, the spark is OK, carburetor is OK, so the only thing left is the gas mixture is not getting into the cylinder, or the exhaust is never leaving.

Just thinking out loud, if the exhaust valve is not opening, I would expect to see some back pressure in the carb.  With the air filter off, see if you can feel puffs of air when it is running on the good cylinder.  Or maybe turn it over by hand and see what kind of pressure you get if you cover the carb with the palm of your hand.  May be able to tell if pressure is coming back from the intake (not being relieved by the exhaust valve)??
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

I'm about to give it up on this engine. I spent another 3 hours switching plugs, coil and wires.
I pulled the head again to check the working of the valves and to see if the head gasket was
still good. Then i pulled the valves and reground them and set to specs. Still nothing. It
wont even try to fire on one side.



 



 



 

Tomorrow I'm changing the point and condenser one more time and then I'm done.
If it does not run I quite.
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

whitepine2

O no you can't quit not after all you have gone through ya gotta make it go and let us know
just what was wrong,you gotta! :P :P :P 8) 8) 8)

Magicman

Well you certainly can't take it to the Junkyard.   :-X
Knothole Sawmill, LLC     '98 Wood-Mizer LT40SuperHydraulic   WM Million BF Club Member   WM Pro Sawyer Network

It's Weird being the Same Age as Old People

Never allow your "need" to make money to exceed your "desire" to provide quality service.....The Magicman

whitepine2

Quote from: Magicman on September 22, 2017, 09:36:58 PM
Well you certainly can't take it to the Junkyard.   :-X

Nope can't do that,it's probably something so simple sometimes ya just can't see
the forest for the trees. I have a feeling K isn't going to give up ether it's not in his
DNA.

Kbeitz

Compression is now the same 105 lbs both sides.
Ran extra hot wire to coil.
Put battery charger on battery for more amps.
Both spark plugs was new. Again

All swapped parts came off another running tractor this time.

carb
intake
coil
valve springs
coil wires
points
head gasket

Whats left to do ???
It looks to have very good spark both sides.
Dumped extra gas down the carb when running.
Valves are working.
Compression good.
Timing cant change only on one side.
One set of points
One carb.
One coil.

I even made my own gas engine from scratch and I had no problem getting it to run.



 

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

Kbeitz

I even had help the last time by someone that works on engines...
He had no clue...
Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

coxy

don't get mad at me but try a set of rings what do you have to loose but a few more hours and a 100 bucks if that don't work ill never give you advice again  :-X :D :D

Logger RK

I would still buy a new coil.  Years ago I had a dirt bike that quit,I changed the spark plug with my buddy's bike. My bad plug worked fine in his, but would'nt in mine. So even though you put one from a running motor, it might be something to consider,especially instead of giving up on it.

Jeff

Just call me the midget doctor.
Forestry Forum Founder and Chief Cook and Bottle Washer.

Commercial circle sawmill sawyer in a past life for 25yrs.
Ezekiel 22:30

Thank You Sponsors!