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Old 02-09-2016, 04:35 PM   #21
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I've been told to never turn a diesel over manually even slowly (as with a bar) since they can pop off and run for a few revs on whatever is in the lines and/or cylinders. Remember...they don't need any "spark"...just air & fuel that gets compressed.

I have hand propped a few airplanes and would not want to see a bar spinning like a propeller. I may have been told wrong, but then...I have never tested the theory.
On an older engine, I'd agree. But with this being electronic the odds of it taking off by barring it over are slim to none. I also doubt he'd be able to spin it fast enough with a bar to get the fuel to combust in the first place.
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Old 02-09-2016, 05:56 PM   #22
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Given that the guy who so advised me was a very old-timer, I doubt he ever worked on anything but all mechs and most those were probably 2 strokes.

But I do know for a fact that a hot, fuel injected aircraft engines can fire with the ignition off and a really short rotation of the prop. And it usually ain't pretty. A trained A&P mechanic at LaPorte Airport near Houston lost a leg that way...so maybe I am a tad spooky on the subject.
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Old 02-09-2016, 11:49 PM   #23
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I wouldn't bar over a 2 stroke diesel unless both fuel and air were both cut off. My 2 stroke Detroit 8v92 starts the first time a piston comes up even when it is stone cold. Its actually spooky to watch. Jack
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Old 02-11-2016, 08:10 PM   #24
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Story time!

I was pulling the radiator out of a 1978 Unimog U1100L, and in order to do so you sort of turn the engine fan while lifting the radiator, so the lower outlet meshes between one of the blades, until the gap points upwards, at which point you pull the rad out of the top. (between fan and grill of cab)

As I got that last turn, the engine, which wasn't cold, caught and started all on it's own because the fuel was set to the idle position instead of the cut position.

So yeah, I know what you mean.


I think the thing is, if you are not sure how to prevent the fuel from getting into the injection pump, and/or the air into the intake while attempting to see if the engine turns freely, I think as a general rule they may need some extra help determining the state of the engine.

That's just a generalization, and shouldn't be taken as a sleight to anyone.

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Originally Posted by Tango View Post
Given that the guy who so advised me was a very old-timer, I doubt he ever worked on anything but all mechs and most those were probably 2 strokes.

But I do know for a fact that a hot, fuel injected aircraft engines can fire with the ignition off and a really short rotation of the prop. And it usually ain't pretty. A trained A&P mechanic at LaPorte Airport near Houston lost a leg that way...so maybe I am a tad spooky on the subject.
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Old 02-11-2016, 11:01 PM   #25
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There was a horrible incident with a truck and transfer. The driver was killed. If you're not familiar with the setup, it goes like this. Truck comes with a load of rock and unhooks the trailer. Truck dumps the load and backs up to the trailer to slide the box from the trailer into the box on the truck. The driver leaves the truck in reverse WITH THE KEY OFF!!! Then the driver goes to the back of the truck where he or in this case she presses a button connected to the starter to move the truck back. Key off, the truck will come back far enough to transfer the second box. Do this with the key on and you die a very painful and gruesome death. You hit that button with the key turned on and in reverse, the engine will fire up and take off. She was pinned in between the truck and trailer.
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Old 02-12-2016, 06:17 AM   #26
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Quote:
Originally Posted by Tango View Post
I've been told to never turn a diesel over manually even slowly (as with a bar) since they can pop off and run for a few revs on whatever is in the lines and/or cylinders. Remember...they don't need any "spark"...just air & fuel that gets compressed.

I have hand propped a few airplanes and would not want to see a bar spinning like a propeller. I may have been told wrong, but then...I have never tested the theory.
Tango,

I've done it with my M1109s and my M1031. No issues because I was working on the fuel injection distributor pump. A couple of times I did it working on other systems, but never had the engines take off and run on me. I disconnected the batteries and that left the fuel shut-off valve on the cut-off position. Always be careful to have that valve in the off position!!!!!!!
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Old 02-12-2016, 03:59 PM   #27
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Good stories by all. The common theme between them all was that the engine was either warm, or the ignition was on. If he bars it over by hand, with it cold, I still doubt that it would start. Don't get me wrong, you do have to take precautions, but I've done it on loads of engines and have never even had the hint of one starting. Bar it over slowly and there should be no worries.
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Old 02-12-2016, 06:38 PM   #28
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Yes, this.

After taking noted precautions, listen to the noise the engine makes when leaking the compressed cylinder past the rings (you can hear a hissing sound of air inside the motor)

If it sounds sort of louder than expected, or seems "too easy" it might be worthwhile to stop and figure out whats going on. If it feels damn near impossible to turn over by hand, you're probably fine.


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Good stories by all. The common theme between them all was that the engine was either warm, or the ignition was on. If he bars it over by hand, with it cold, I still doubt that it would start. Don't get me wrong, you do have to take precautions, but I've done it on loads of engines and have never even had the hint of one starting. Bar it over slowly and there should be no worries.
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Old 02-12-2016, 06:58 PM   #29
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I'm a diesel novice so I apologize if this is comes off as snarky (it's not).

Couldn't he just pull the glow plugs to relieve cylinder pressure? Do they work like a spark plug in that it's sealing up the chamber?
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Old 02-12-2016, 11:32 PM   #30
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Good compression is one of the signs of a healthy diesel engine. If you remove the glow plugs, you can't check compression.
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