Oil & Fuel Diesel engine shut-off "shudder"

ArkCivEngr · Jun 9, 2005

Diesel engine shut-off \"shudder\"

Just curious as to what causes this. My JD X495 and the Cummins in my pickup both do what I call "shudder" when shutting off the engine. It's basically just intense shaking for about half a second as it quits. I've seen others do it; apparently it's normal.

The odd thing is that the engine on my Kubota L3400 doesn't. It shuts off very smoothly.

So what causes this "shudder," and why doesn't the Kubota do it? /forums/images/graemlins/confused.gif

joecdeere · Jun 9, 2005

Re: Diesel engine shut-off \"shudder\"

It's just the cylinders firing on the last breaths of fuel they get, as it stops the cylinders drop out as they run out of fuel, and an engine as heavy as a diesel will tend to shake as cylinders quit firing. Things just aren't balanced as this is happening.

hudr · Jun 9, 2005

Re: Diesel engine shut-off \"shudder\"

I have a 6.5 chevy w/ a 5 speed tranny. There is actually a damper on the flywheel to quell some of that shut down shudder. The motor used to die really hard w/ lots of shaking. I had the tranny rebuilt and had to get a flywheel in the process. When I first got the truck back it was almost gas burner like on shut down. Now the shudder is starting to creep back in as the damper wears. Anyway, I agree, a diesel has a lot of heavy parts moving around. They just don't shut down like other stuff. I remember all those Macks we used to have and how the big 6 motors rattled on shutdown. Diesels just don't like to quit, they want to keep running.

Partsman2 · Jun 10, 2005

Re: Diesel engine shut-off \"shudder\"

My Kubota BX2230 does it but my JD 4710 doesn't. All of the small Kubotas I've seen do this. I had never seen it with any other diesel.

garchib · Jun 10, 2005

Re: Diesel engine shut-off \"shudder\"

My 4100 does this as well, so I guess it might be a Kubota painted green ?! /forums/images/graemlins/grin.gif

SkyPup · Jun 10, 2005

Re: Diesel engine shut-off \"shudder\"

The best way to avoid the shut down shutter in a diesel engine is to have an electronic solenoid valve in the air intake that blocks the air 100% when the key (and the fuel pump) is turned off. That way there is no shudder as the engine dies instantly.

Highbeam · Jun 10, 2005

Re: Diesel engine shut-off \"shudder\"

I was always told it was the high compression of the diesel that causes the rough shut down. As the fuel is cut off and the engine slows down it has less and less momentum to overcome the high pressures at Top Dead Center so as it compresses the air it slows and then as it gets past TDC it speeds up again like a bouncing ball. There's nothing smooth about how a diesel engine stops when you have 3-6 of these bouncing balls.

This isn't as obvious on a gas motor with less than half of the compression ratio and lots of dampening but still exists.

Jagmandave · Jun 13, 2005

Re: Diesel engine shut-off \"shudder\"

Is the idle set right? Maybe it's coming down from too high an idle RPM?
My 3 cyl Yanmar shuts off like the just crank seized! It just stops........

coveredbridge · Jun 13, 2005

Re: Diesel engine shut-off \"shudder\"

</font><font color="blue" class="small">( Just curious as to what causes this. My JD X495 and the Cummins in my pickup both do what I call "shudder" when shutting off the engine. It's basically just intense shaking for about half a second as it quits. I've seen others do it; apparently it's normal.

The odd thing is that the engine on my Kubota L3400 doesn't. It shuts off very smoothly.

So what causes this "shudder," and why doesn't the Kubota do it? /forums/images/graemlins/confused.gif )</font>

I don't know what causes it, but my bx1500 (40 hrs) shuts down and starts up that way /forums/images/graemlins/confused.gif. My JD 820 (5400 hrs) on the other hand, starts and stops very gently. Maybe it's a function of operating hrs?

dieseltoys · Jun 14, 2005

Re: Diesel engine shut-off \"shudder\"

The type of engine mounting has a lot to do with the amount of shudder the engine creates on shutdown. Rubber mountings absorb higher frequency engine vibrations while the engine is running but on shutdown when the engine's internal motions slow down and become less smooth and balanced, the mount cannot dampen the motions and it is felt through the machine as the engine is allowed to shake. Many tractors, such as the 3400, have the engine bolted solid to the transmission and are part of the framework of the tractor, therefore the mass of the entire machine acts as one. So when the engine shuts down the internal inertias are overcome by the mass of the entire machine and little motion is felt. Usually on larger machines the higher frequency vibrations are isolated from the operator through rubber mounted operating platforms, seats and steering. A good example of how speed and compression affects the smoothness of an engine would be to try to pull the starter on a chainsaw or string trimmer slowly and you will find it uneven and hard to pull at a smooth steady rate. Give it a quick pull and the cylinder pulsations are less noticable. Now remove the spark plug and relieve the compression and it becomes very smooth to pull.