Detroit Diesel 3-53 would not stop after air intake closed? WTF?

I would guess that with the valve cover off, the engine is breathing through the "breather" hose on the valve cover? Normally the breather would be applying vacuum to the valve area & crankcase and only "breathing" the limited amount of blowby from past the rings... but with the valve cover off it's "breathing" fresh air?

Either you have a leak in your intake manifold, or leaky intake valves, or it's sucking air past the rings from the crank case. Or I have my head up my ass -- I'm no diesel mechanic, nor a truck driver.

I thought diesel engines were supposed to cut off fuel to stop, and only cut off the air as an emergency stopping measure?

I was told, a long time ago by someone who wasn't a diesel mechanic (but did drive them quite a bit, and pay for them when they broke) that a diesel can 'run away' by sucking both air and crankcase oil past the rings, and be unstoppable until it has seriously depleted the lubricating oil.

I:

1: don't know how often that happened. 2: don't know if it's true at all (but it was my dad, who didn't usually exaggerate, and who was in a position to know) 3: don't know if it's common now, as opposed to the mid 1970's when I heard it.

I owned a Volkswagan Rabbit diesel for a little while. The rings were worn and after a few weeks about an inch of crankcase oil would build up in the air box. Hitting a bump or going around a tight curve would slosh the oil into the intakes and give you a very exciting 5 seconds of about 150% full throttle. Especially if you were in that tight turn at the time.

I learned to pop the airbox open and mop out the oil about once a month.

That sounds plausible. Also wondering why he isn't using a fuel shutoff to shutdown like every diesel I've operated uses.

Here's a little update. This is sort of a "reply to all", I am reading everything that you guys post, and this is my update.

I have learned to run this diesel a little more safely, so that I do not freak out.

First, I added a ball valve on fuel intake, so I can easily shut off or restrict fuel at any moment.

Second, I start the engine with intake mostly blocked by that infamous board.

This way, the engine does not run frighteningly fast. It runs relatively slowly, is starved for air, smokes a lot, and I can shut it off by simply shutting off my ball valve on the fuel filter.

While it runs slowly, I can afford to experiment a little bit. Neither of the two controls does anything that I can perceive.

My feeling is that I need to read up the manual on how the governor functions in this engine.

Lastly, even when the engine ran too fast and too loud, the output pulleys seemed to rotate at a fairly reasonable speed. So perhaps I am just a little bit too girly and too sensitive to the noise of a two stroke diesel. But I do not want to take chances on this.

i

Great idea. Thanks.

I have added a fuel shutoff just 5 minutes ago. It helps in getting the situation under control.

Yep BIG mistake. With the VC off the engine now has an intake path for air. Through the crankcase via the oil drains and crankcase vent lines. Detroits are two strokes. They pass the intake air through the crankcase to vent any vapors (this is also why they like oil, they suck out any oil misting in the crankcase) and then it gets run into the engine through the separator.

BTDT with a couple Detroits. The BEST way to shut ANY diesel down is with a fuel shut-off. Shutting off the air intake is the last option. That is because the high vacuum that it creates can damage seals in the scavenging pump and intake.

Maybe I have my head up my ass too.

I have added a fuel cutoff valve.

I thought that it was all about just sucking oil, not air. That is a very scary possibility.

i

NOT a good idea. That WILL damage the engine, you control the engine speed using the fuel throttle NOT air.

Gee ya think!!!

Detroits run normally at 1900-2100 rpm. Much over 2400 and they start to destroy themselves. They are THE NOISIEST diesel out there. They also can be set up to make more power than any other engine of the same size due to being a two stroke.

A chap I used to know, now dead, told me lots of interesting stories from when he worked in construction and some of those included large earth moving machinery where the diesel engines ran away. In one case the operator realised what was happening and drove the machine into the tunnel wall to stall it before any serious problems occurred. Those big machines in question had oil bath air filters IIRC and in some cases the engine would start to run on the oil in those. The chap had an interesting life, he said on another occasion he was almost killed by shrapnel from a generator donkey engine exploding when someone used compressed oxygen to start the genset rather than compressed air, that was when he was working on the Aswan dam.

I think that I got it, thanks to you and Phil P from SmokStak.

The cause of this runaway condition is that a rod that is supposed to regulate the injector, failed on one of the three cylinders.

See just one picture here:

Any idea how to get it "unstuck".

thanks

i

Maybe valve seals are shot?

You commented about how fast the engine seems to run, even tho pulleys, etc, don't seem to be going so fast. As one guy said, this is a 2 stroke, so it makes twice as many power pulses as what may sound normal to you. We still have some of them around in farm tractors. You can hear them 2 miles away, sounding like they are running 10K rpms. I see that you found a bad part. Good. But just in case, my Case 800 Diesel's fuel pump-distributor/governor are two separate machines within a more or less common box. The governor connects to the distributor with a little link. Once, while out in the woods bringing home firewood, the link came off inside the thing. I totally lost rpm control. I shut off the fuel, but the thing kept going, winding up as it went. Exhaust manifold glowed red. I finally clamped a vise grip on a flexible part of the fuel line to stop it. Scary. It was 8 or 10 years ago. Engine still runs fine with rebuilt distributor system. The moral: make sure the governor is connected where it can do some good.

Pete Stanaitis

----------------

A very scary story. Thanks for sharing. I will work on it, when time and weather permits, which may be a while from now.

Ignoramus31413 wrote in rec.crafts.metalworking on Tue, 21 Jun 2011 13:01:38 -0500:

That's good. But figure out how it's supposed to be shut off. Cutting off the fuel before the injector pump starves the injector pump of its only source of lubricant. At slow speeds you can get away with it, but if you had it at high RPMs and did it too often, you might kill the injector pump. More of an issue with a truck or something if you were to run the tank dry and coast down a hill.

You should be able to hold the throttle (linkage to the injector pump?) closed, to stop the engine.

The issue is that one injector was stuck. I will probably just get a new one if I cannot take care of this one easily.

i

I just watched it 10 minutes ago. Sad

i

Bad gasket between the intake and the blower, for example.