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CarlH

Why Won't My Diesel Run?

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CarlH
Well, actually, it WILL run but won't stay running longer than 40 - 60 seconds. It starts when cold, then dies and won't start again until its cold. I rebuilt it 2 - 3 years ago and had been using it as my regular mowing tractor when it stopped running. It has always tended to be reluctant to start when hot. When it dies, its like the load has been turned up on a dyno and the engine just goes to sleep. My first thought was fuel. Swapped injectors, injector pump, put on electric lift pump. Cleaned tank and replaced filters. Fresh fuel several times. Still the same behavior. I could conjecture mechanical things like rings going solid with temperature or valve lash tight but I used it many hours before having these problems. I gapped each ring when I installed them (not to say I couldn't fouled that up though). I would expect valve lash to loosen up over time not tighten. The only other bit of data is that I've never gotten any black smoke out of the stack so I doubt its running rich. Any ideas are welcome.

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Dark
possably check the head for crackes when the engine warms up the crack gets bigger then releases all compression. rings would cause black smoke valves if to loose may cause compression loss glow plugs only heat the cylinder pressure regulater if equiped would cause lean out some engines also have a compression release (if equiped may case problem)

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D-17_Dave
I'd check the valve lash. A valve can heat up and streatch whitch will slowly loose compresion. Then I would replace any old fuel lines you have on the tractor. A serious restriction can seep fuel by it but not flow enough to run. You say it will start right up when cold does not sound like fuel. If the valve lash checks OK then I'd pull the head and do a visual inspection of things like any burn marks on the valve seats and piston/cyl. issues.

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2burning
The exhaust valve adjustment has that compression release setting on it too. Is the kill cable doing ok? This site mentioned mixing in 10% clean motor oil with the fuel to see what happens on a hard hot start (for a GM V8 though): http://flashoffroad.com/Diesel/troubleshoot/starting.htm It still does sound a lot like air in the fuel lines though...

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CarlH
Thanks for the link, I will study it also. I don't believe the Lombardini diesel has a compression release associated with the exhaust valve. This model has no compression release period. The models with compression release use a petcock that is manually opened. I will check the kill cable adjustment - good idea.

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arnoldir
I don't know if this is applicable, but here's my 2 cents. I have the Lombardini 28 HP twin on Magnatrac 6000 crawler. It is equpiiped with a combined fuel filter and shutdown solenoid mounted on the fuel pump side of the block. It developed the problem that you describe, sounds like it was running out of fuel within 30-60 seconds after starting and needed to sit a while to restart. I removed the entire assembly and replaced it with an in line filter, and she regained normal operation. I have left it this way, and just use the manual kill cable to shut it down. Good luck.

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acken
On some diesels a plugged return will act just like you describe. I don't recall how that one is routed without looking at mine. Some can be tested by removing return line at injector, and let it run out (messy).

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2burning
quote:
Originally posted by CarlH
I don't believe the Lombardini diesel has a compression release associated with the exhaust valve. This model has no compression release period. The models with compression release use a petcock that is manually opened. I will check the kill cable adjustment - good idea.
I stand corrected, I see the release is optional and not on the ones put into our 7790/920D's Sorry.

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CarlH
Not much time to play with work on the diesel tonight. I did check that the return line was clear and the stop cable was not holding the stop lever partially closed. I dug out the Lombardini service manual and was reminded that the cold valve clearance was specified at .006" to .008". I vaguely recall that when I rebuilt the engine, I set the lash a bit looser than that though because it seemed a bit tight. Maybe a little more play time tomorrow evening.

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2burning
Another idea just remembered, to check for air in the fuel lines, a person could replace the return line and maybe even other lines with a piece of clear tubing to see if there are any air bubbles appearing.

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haykarenhardy
I was looking for oil for my new 7790. The Manual calls for S.A.E. 40 over 68 degrees, 20W for 32-68, 10W -4,32 and 5W -4 and below in a CD( DS series 3 ) service classification. Do not use multi-viscosity oils. I know this manual was written in 1985, but I can only find a 40, 20W or 10W in a SM/SL oil. I found 30w in a CJ oil and 15W-40 in a CJ-4/4SM oil. What type of oil should I use? Stan

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olcowhand
Sounds like fuel delivery problem. Without reading back, did you change fuel filter? These pumps make super pressure, but don't pull fuel at all. Gotta have good fuel delivery with not a bit of air getting mixed with the fuel.

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CarlH
Stan, AMSoil has several multi-viscosity synthetic diesel motor oils. I have been using 15W-40 in my Lombardini. Thanks to everyone for your inputs. I will try them when my schedule allows a little time.

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