Runaway diesel
- Thread starter Captain Larry-DH
- Start date
My thoughts - pretty close to deadly.... As in, it could kill you.
Candidate for the Darwin awards.
dj
Actually, it should make you nervous. Hand cranking an engine requires knowledge of technique - body position, the way you hold the crank, and how you spin the crank.
I forget about these things because I was taught how to hand crank engines from a very young age by my grandfather. OK, so I'm old, you can imagine my grandfather was a lot older, and lived through the dawn of the combustion engine. Of course the early engines were pretty finicky...
I think an option might be to get a second hand crank, modify it so you could run that modified hand crank with a drill. That way you still have to proper connection to the engine.
Also, thank you for bringing this up. It's a really important point...
dj
I didn't know that the new diesel engines are actually four cycle not two cycle as the earlier small diesels were. Thanks for the discussion.
Worse is when the prop takes your head off...
Yeah, those were the planes I learned to fire up... Those you get taught before trying...
dj
My thought was to get the engine spinning, pull off the drill and close the decompression levers.
Mark
It would not likely work. You need power on the crank going through the compression stroke where the engine fires.
dj
I had a simular thought as well. On my Universal M25XP, I cannot get a socket on the crankshaft nut without lifting the engine off its mounts so that is a non-starter. I can get a socket on the alternator bolt and turning it clockwise will cause the engine to spin in the correct direction.
Possible system.
- pull compression release handle [one lever controls all three cylinders].
- Use drill to turn alternator which gets engine turning over.
- When at max speed the drill is able to produce, pull the drill back to let engine freewheel and drop the compression release.
In my experience with hand cranked diesel engines, you won't have enough stored energy in just the fly wheel to start the engine. The fly wheel stores enough energy to give the hand crank energy provided enough back up energy to push the piston through the compression cycle fast enough to fire. This especially applies to Yanmars.
Not saying don't try it, but if you actually do get it to work, I would certainly love the hear about it. Just don't try to keep that socket on through ignition.
dj
Agree. I would not want to be connected to the nut if the engine fired.
If only I had a ratcheting socket adapter. So I typed it into Bing and what do you know!?!?
Performance Tool 1/2 Dr. Ratcheting Adapter W32137 - Walmart.com
That might work, but bear in mind how the hand crank connector actually works. When the engine fires, it actually pushes the connector off.
There is also the issue of speed of rotation to fire. Do you have a touch tachometer? If you do, you might want to measure the RPMs of that alternator nut when the engine is at idle. There is a minimum RPM a diesel engine has to spin in order to fire. I don't recall what that is but it's probably close to RPM at idle. If you can spin up to at least that, you'll have a better shot at starting the engine.
dj
It is not correct that you need a minimum rpm to fire. With a compression ignition engine, the injectors always spray the fuel into the cylinder after top dead center. If there is enough compression, the diesel will fire and provide the rotation to continue to run. Back in my Motana cowboy days, the one tractor that we could always get to start was an old Massy Furguson which was hand cranked. You would slowly turn the engine until you felt the start of the compression stroke with the handle at 10-oclock. You then give one hard pull from 10:00 to 2:00 which would take that cylinder past TDC and fire. Even in -20º temperatures, it seldom took more than two or three tries. As somebody else stated, a diesel is very unlikely to kick back because it cannot fire until the introduction of the fuel which is after TDC. Gas engines always have the spark before TDC so you need enough inertial to force the engine to keep rotating over the top after the gas has exploded.
One other thing I am thinking about testing is a way to heat the engine to assist in starting. The Universal really benifits from glow plugs. IF the problem is a dead starter, you would still have the glow plugs so that ould not be an issue. If the problem is a dead start battery, I have the ability to link my 560Ah LFP house battery to my start battery so I could do that.
I wonder if it would be possible to open the compression release and then blow a hair dryer down the intake which should flow warm air through one of the three cylinders. Then rotate until the next opened, etc. After a few minutes of this, you should have a fair amount of the steel heated. It would also be of benifit to blow the hot air down the intake as the engine is cranked. In principle, this is the same way that the grid heater works on my Cummins. If all batteries are dead, I could not do this alone but could run an extension cord from a buddy boat tied alongside.
Interesting thought exercise.
I wonder if it would be possible to open the compression release and then blow a hair dryer down the intake which should flow warm air through one of the three cylinders. Then rotate until the next opened, etc. After a few minutes of this, you should have a fair amount of the steel heated. It would also be of benifit to blow the hot air down the intake as the engine is cranked. In principle, this is the same way that the grid heater works on my Cummins. If all batteries are dead, I could not do this alone but could run an extension cord from a buddy boat tied alongside.
Interesting thought exercise.
That's not been my experience. We've diesels that wouldn't start simply because the starter motor wouldn't turn the engine over fast enough. Might be engine dependent though.
dj
I've done it several ways, using a burning rag held near the air intake, using a propane torch with the flame aimed into the air intake...
dj
My Perkins will squirt a little diesel into the air intake, start it on fire with a glow plug , then suck the fire into the cylinder for cold start. I think this is a common system on older engines but I was always a little worried about starting a fire on my boat. I must say it works well even when the batteries are a little down.
That can't be the case because 1) nobody could ever spin a hand crank 800rpm to start the engine, and 2) I know for sure my engines start before the starter ever gets them to 800rpm. They usually start on the first or second compression stroke of any cylinder, which is almost instantly.
The reason a weak battery/starter can't start an engine is because it can't push it through the compression stroke.
Mark