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Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke


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  #51  
Old 01-10-2018, 11:02:36 PM
zuhnc zuhnc is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

In regards to compression pressure: searching the Onan publications reveals this information, copied and pasted from the referenced document. - From Onan document 967-0751 – Compression Testing:

The cylinder compression test can be used to determine the condition of valves, pistons, piston rings and cylinders.

To check compression, run the engine until thoroughly warm. Stop engine and remove all injection nozzles. Insert the compression gauge in one nozzle hole. Crank the engine and note the reading. To check for piston blow-by, squirt a small amount of SAE 50 oil into the cylinder and repeat the check. An increase in compression indicates piston blow-by.

Compression of a standard new engine cranking at about 300 rpm is about 300-350 psi (2070 to 2415kPa) prior to Spec P and 350-400 psi (2415 to 2760 kPa) Spec P and later. Compression should be fairly uniform, normally with less than 10 psi (69 kPa) difference between the highest and lowest cylinder, taken at the same cranking rpm. Excessively high readings indicate carboned combustion chambers.

Thought everyone would like to know there IS a number published by Onan. I would presume these numbers would also be good for ANY J-series diesel engine. zuhnc

As an aside, the very first Onan diesel I worked on was an MDJB, in about 1975. It was extremely hard to start, even with extensive preheating, white-smoked heavily, and would only carry about 1/2 load. No one knew what the issue was. Boss said "fix it". I found out, after extensive reading of the manuals, and other documents, that the pump (PSU) was 180* out of time. Fuel injection was toward the end of the exhaust stroke, but there was enough fuel left in the cylinders to start and run. Corrected the timing, it started waaaaay easier, and would carry full load with no problem. zuhnc
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  #52  
Old 01-22-2018, 01:51:21 PM
sscummins sscummins is offline
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Ok everyone, I got back from vacation and batteries all recharged and feeling great,

So great I had to dive in and check my flow timing, and the fuel stops (maybe a hair less) 1 and 1/2 teeth AFTER P/C mark on flywheel. Checked it double checked and triple checked it with exact same results. BTW, it seemed very simple of a test to do.

Please advise?
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Old 01-22-2018, 02:36:32 PM
alco539 alco539 is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

If I understand what you are saying correctly, then the pump timing is substantially retarded. I would have to look at my ring gear to measure it but I am thinking it would be be measuring nearly 1/2" retarded. You are going to have to get an exact measurement to determine exactly how much thicker the timing button will need to be. Directly from the AMBAC M-50 manual "To select correct button size, carefully measure space between PC mark and timing
pointer. Each 0.100 inch (2.54mm) on flywheel circumference is equivalent to 0.003 inch (0.076mm) button thickness."

That seems like a lot out of time to me. If this pump has been know to run correctly at one time then I would make absolutely sure that the pump and cam gears are in the correct mesh/time. It may be off one tooth.

Jimmy
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Old 01-22-2018, 03:46:27 PM
sscummins sscummins is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

i BOUGHT IT NOT RUNNING, damn caps lock,
had pump and inj rebiult.
got it running in its current condition.
checked pump position and at first it was about 1 tooth off when i installed it, i made a widest puin to lock in place and it seems to be right in the middle of the play in hole of pin compared to flywheel p/c mark.

Please advise,

thanks steve
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Old 01-22-2018, 04:32:36 PM
alco539 alco539 is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

Since the pump has been rebuilt, then the timing could very well be off from original. If you have the pump installed at the PC mark and it is pinned at the correct point, then using the flow method make your measurement how far past the PC mark the flow stops then calculate which timing button you need.


Jimmy
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Old 01-22-2018, 06:11:54 PM
sscummins sscummins is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

I read this in the manual
If the spring is not seated properiy the valve holder can be tightened only about one-fourth of the way down.When the spring is properly seated the valve holder can be tightened about three-fourths of the way down by hand. Make certain that the spring
is seated properly in the valve holder and on the delivery valve before torquing.

I noticed the seat was all the way in and when i threaded the cap/valve holder in I was able to thread all the way in , also it did not have a gasket copper or other material, also it did not look like either of the older or newer models according to figure 49 and 50 in manual 974-0750. it looked like both together, threaded sleeve with cap nut on end and it was tapered both body of pump and cap nut head matching for sealing.
is there a 3rd type of pump?
should there be compression on spring to delivery valve?
also it looks like both valve holder from fig.49 and cap screw from fig 50. note i did not try to seperate the cap nut from valve holder if thats possible?

please advise,
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  #57  
Old 01-23-2018, 03:30:37 PM
sscummins sscummins is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

Good morning (if ur in my time zone) to all. First I want to thank everyone again for all your patience with me being a newby asking and learning. I know I probably was getting on at least 1 or 2 of your nerves.
But I have found out from another source the possible smoking gun and wanted to share with everyone as you all have shared your knowledge with me.
Spoke with Mark at deisel fuel inj in portland or. and what he caught from my explaining of what I did and noticed as I was preping and putting back together for the flow timing test, he said that the cap nut and the valve holder are 2 separate pieces, also mentioned more than likely the pump was put together incorrectly during rebuild cause a loose fit against the valve holder to the spring and delivery valve. Makes sense now that I understand a little more of this Pump.
So what I am going to do is when I get home tonight, take off the 15/16 cap nut and un thread the valve holder from it and make sure I have the cap nut gasket in there then insert spring and then screw in the 5/8 12 point hand tight making sure it gets harder at 3/4 way in like book says, torque 70 - 75 loosen and re torque to 60-65 thenj cap nut and gasket torque to 50-55 loosen and re torque to 60-65 and hopefully white smoke will be gone.
does anyone have any other suggestions?

Steve
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  #58  
Old 01-23-2018, 03:43:04 PM
nothingbutdarts nothingbutdarts is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

Here's the thing in my mind, if the outfit that had already rebuilt it couldn't put it together correctly how in the heck could they have calibrated it correctly?
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Old 01-23-2018, 05:19:09 PM
Wayne 440 Wayne 440 is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

Quote:
Originally Posted by nothingbutdarts View Post
Here's the thing in my mind, if the outfit that had already rebuilt it couldn't put it together correctly how in the heck could they have calibrated it correctly?
It would not be the first time that good money has been paid for incompetent work at a diesel injection shop.
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  #60  
Old 01-23-2018, 06:38:49 PM
sscummins sscummins is offline
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Default Re: Onan 12MDJC-3R/2268D Serial #16c859299 White Smoke

I dont know, It does make sense with it being loose

causing all the smoke and excessive fuel usage, Cant wait to get home a get it put together right

One more thing I know is I wont be going back for any work to be done at that shop in florida.

The guys in Portland were walking me through how to change the button if needed until he heard what i said about the parts coming out together..

Have a great night everyone, I will follow up tomorrow if I actually get the time to work on her tonight.
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