Cummins 4BT & Diesel Conversions Forums banner

21 - 35 of 35 Posts

·
Registered
Joined
·
67 Posts
I'll throw my 2 cents in here as well. As a former fuel injection tech, I'll share some insight with everyone.
First, I'm not sure how many of you are familiar with the German engineering philosophy, but in a nutshell it has two rules. It's right, or it's wrong!
When I first started rebuilding VE pumps I thought they were the most persnickity little [email protected][email protected] I'd ever seen. And why in the hell do you need all these little gadgets and fixtures and gauges to rebuild one anyway? It was running (well, kinda) before, so it should be close enough now right? WRONG!
After attending the Bosch training school and getting certified I realized that if you actually use all those cute little gadgets and guages instead of just dusting them once a month and staring at them, the pump is 95% right before it ever hits the test bench.
Point being, there's some engineer somewhere who has more thoughts in a second than I'll have in a week, who thought all of this through and designed all those tools to make the job almost fool proof, if you use the tools.

So here's the thing with the factory calibrations. GM designs the step van then goes to Cummins and says, "We'd like to purchase xxxxx engines. They are going in a xxxlb delivery truck with a xx coeficient of drag, top speed ofxx, and needs to operate at all temperatures and altitudes found in the US at any given time of year. So that's what these little guys are set up to do.
Me personally being in South Carolina, I could give a rip if the thing runs well at -20F or how it runs at 10,000ft above sea level. Those in northern Canada probably don't care if there engine would overheat if the ambient temperature rose above 90*F. As stated earlier, think about what you're doing before you do it. If you live in south Florida and don't feel like running a cold starting aid, don't use it. If you live in Minnesota, may want to rethink that.
It's not to say you can't tweak your engine for more performance, but just know which features will be affected, and be sure you're not shooting yourself in the foot.

One last point, and I can't stress this enough. Governors on a diesel are designed to shut off the fuel at a specific engine speed. If the governor is not adjusted properly, you may render this feature inoperable. I would hate to hear of someone who went to all the trouble and expense to fit one of these engines in there truck with all the go fast goodies, only to have it run away and chunk a rod through the fender the first time they fire it and blip the throttle. A runaway diesel is nothing you want to experience, trust me. They can and have killed people.
If you think you may have done something to cause this, stop and ask before you hit the starter. And always be prepared for a runaway. Be ready to cut fuel and air to the engine if neccesary.
This doesn't mean have the wrench that fits the fuel line laying on the bench across the shop. Have it in your hand, preferably on the fitting while a helper hits the starter. It may seem like overkill, but how much did you just drop on that engine again?
Have fun with it, but be safe while doing it!
Later,
SS
 

·
Moderator
Joined
·
3,907 Posts
SS, on the aversion (or shutting down of) a runaway on initial firning (after whatever tweaking), I wholeheartedly agree on the "have it in hand", but I always thought the accepted method was to cut off the air.

Can you shut the fuel supply off with a wrench (ie unhook the line) fast enough (perhaps counting on drawing air into the fuel)?

Not on the prod here, just asking.
 

·
Registered
Joined
·
67 Posts
No problem Erik. It's true you can shut the engine down by starving for air, but it's hard on the engine. Here's an off the wall example for you. Two athletes, one diabetic, one not, are having a race. Close to the finish line the diabetic's sugar drops and he slows down and stumbles. An angry fan jumps the fence and chokes the crap out of the other till he passes out. Kinda off the wall, but you get the point. Here's the problem with choking the engine. Let's say you have all the plumbing connected exept for the air inlet to the turbo. So you decide to fire it yourself and hop in the driver's seat and hit the switch. The engine catches and heads for the moon. By the time you get out of the truck, run around the door, trip over the jack stand, almost skate on the creeper, and get the board, the engine could be close to 6k or above. It's very possible for the engine to suck the oil right out of the turbo and suck the seals out of the front and rear main. Thus filling up the aftercooler or dumpin it right into the engine and burning it for fuel. Detroit used to have an emergency shutdown flapper on the air side of their engines, and more than one has ran away due to a stuck rack. When the operator realized there was a problem, they would pull the flap, and the engine was turning so fast it could suck every seal on the motor and still get enough air to hang on long enough to burn most of the oil out of the engine.
One other thing to remember is if you're going for the injectors to shut it down, remember to wear a glove because of the high pressure fuel. I used to keep an inlet fitting for the 855 cummins in my toolbox that was drilled out very thin and made of brass. That way if I ever got into trouble I didn't have to worry about wrenches or boards, just leave a large hammer on the tire and give it a whack.
It's just like the precautions for modifiying the engine, think it through before you do it. And you only need the helper once. It's not like the engine will run away because you hooked up the air conitioner or added an oil cooler.
Think it through, and do a dry run with your helper before you hit the switch. Make sure you're both on the same page about what's supposed to happen, and what each of you will do if something goes wrong.

Something like this:
Erik: Okay Bob, let's fire it up. But first, here's what should happen. You hit the starter. If it doesn't start after ten seconds, stop cranking. If it does, I'll work the throttle.
Bob: So I just work the key and keep my foot of the gas, got it.
Erik: Now, when it starts I'm gonna let it idle for a few seconds and then give it two short blips and return to idle.
Bob: Two short blips, got it
Erik: Then I'll give it one good full throttle goose. As soon as it reaches full speed, I'l let it return to idle. If the engine is accelerating for more than two seconds or you see me running, kill the key and be ready to go for the air if neccessary.
Bob: Two seconds, kill the key, go for the air. But what will you be doing, Erik?
Erik: I'll be on the other side killing the injectors. So hop in but don't hit the key and let's go through it to make sure we have a clear path and all the tools are right there.

Sorry for the novel, but you get the idea. I don't mean to scare anyone away from tweaking their engine, or make them afraid of these engines, but just be sure you know your limits, and that you've thought it through. Have fun and be safe.
Later,
SS
 

·
Registered
Joined
·
808 Posts
I must disagree. You are mentioning two different conditions, engine over speed and a true runaway.

When people screw with the IP and governor spring sometimes they get to a point where the engine is no longer governed with the governor. The engine goes into over speed, yet its running on diesel fuel fed from the fuel tank. Simply shutting off the fuel, ie; Turn off the key (fuel Solenoid) closes and engine no longer gets fuel and stops. Or you can pull the manual fuel shut off on the Bosch VE to also shut down the fuel and stop the engine. Remember the engine is running on the diesel fuel supply even though its in over speed.

A true runaway is caused by lubrication oil being drawn into the engine and creating its own fuel source. A true runaway can also be caused by the engine entering a atmosphere where combustible or flammable vapors are present. These vapors now become the fuel source. In either condition, the lubrication oil or combustible/flammable vapors have now become the fuel supply. Shutting down the diesel fuel with the fuel solenoid valve or the manual pull will NOT shut down the engine. In this condition of a true runaway, the only way to stop the engine it to kill its air supply. If a true runaway happens, events happen fast and the engine will climb in rpm's like a home sick angel. To save the engine, it must be stopped NOW. This is why all my trucks run Rhoda Deca air shut downs.............just in case.

Good reading here;
http://www.pump-zone.com/valves/valves/controlling-runaway-diesel-engines.html

http://en.wikipedia.org/wiki/Diesel_engine_runaway

http://en.wikipedia.org/wiki/Overspeed_(engine)

Also google "diesel engine runaway"

Paul
 

·
Registered
Joined
·
1,366 Posts
That was one of my fears when I first put my 4BT together. I had introduced a lot of air into the fuel system, replaced the governor spring and turbo without having started the engine. I feared a troubleshooting nightmare in case something went wrong, but fortunately the engine ran well after I bled the injectors.
 

·
Registered
Joined
·
2 Posts
This is only a suggestion for the newer folks with limited Cummins engine exposure and pertains to doing multiple engine repairs to a running engine and ending up with an engine that will not start.

The first thing you should do is a test run of your engine immediately after your purchase. Test runs should be limited to no more than a 30 second run without coolant. This does not mean run 30 seconds and shut off and immediately restart. The early engines with the 9 mm injectors have enough head failure problems with head cracking in the injector to valve seat area without any additional encouragement. If possible test the engine with a temporary coolant system connected. This will show if there are any problems with a head gasket leaking coolant. I personally would NEVER buy or even consider buying a Cummins B series engine that was demoed on Youtube or anywhere else showing a run time of over one minute without coolant. Of course, you may get lucky or your results could vary. That's your own personal choice.

EDIT: I can't believe I omitted this! BUY, BEG or BORROW a service manual BEFORE you begin any repair. There are a few unique procedures that in implementing are different from the things that you may have learned in repairing other engines. The service manual also shows tolerances of service acceptance on questionable components, ie; cylinder head cracks.

Do a compression check. This procedure can be found in the Tech Topics Index. Use the correct test gauge! These engines are far easier to work on whenever they are out of a vehicle.

Check your crankshaft end play. It should not exceed the approximate thickness of a matchbook cover. If in doubt, buy or borrow a dial indicator and make sure. There is a well know thrust bearing problem found in some of these engines. This procedure can be found in the Tech Topics Index.

On a running engine, if you find that you need to replace a head gasket, reseal the injection pump, replace the lift pump, install a governor spring, replace the injectors, I highly recommend the following to be incorporated. Incorporate only one component repair at a time and restart the engine. Then on to the next item to be replaced. It seems to be a very common recurring situation where a person unfamiliar with one of these engines does multiple repairs and ends up with an engine that will not start. This creates a situation of many variables and turns the usual long distance internet diagnosis into a nightmare kind of crap shoot. IE; replace the injectors and restart, reseal the pump and install the governor spring and restart; replace the head gasket and restart; etc. This narrows the problem down to only one repair and makes troubleshooting focus on only one problem area. Granted you may need to repeat removing the injector lines but that is a lot easier than trying to sort out multiple repairs that have multitude of possibilities.
Very practical and informative article I did some of these suggestions before.
 

·
Registered
Joined
·
54 Posts
Detroit runaways are the best! But not the stuck rack runaways, they're pretty lame, Detroit put just enuf return spring on the injector plungers to make rated rpms plus a few extra, so they wind up and start missing.
The absolute Best are a crankcase full of fuel, or about a half gallon of motor oil in the airbox, haven't seen a great one on YouTube , YET!!
You know a good ones Comin when she gets a little eradic, exhaust looks a little off, you got about one second to find the emergency or
whatever. Hats off to the guys running Turbo motors without an emergency shutdown on it.
 

·
Registered
Joined
·
521 Posts
Good calls here on this thread. This is making me rethink my governor spring and doing it in the truck after I confirm a good start and idle with the known good pump and settings. Thanks for reviving this.
 

·
Premium Member
Joined
·
289 Posts
Having worked on electronic,electrical and mechanical things or supervising others in that endeavor I found out a long time ago to read and understand the technical literature dedicated to that specific piece of equipment and to a great extent trust the engineers that designed that piece. If technical literature is not available spend an inordinate amount of time learning the piece and understanding how it accomplishes what it does what it was designed to do. If you do not understand something about it find out or get the assistance of someone who does. This advice from Bob about doing one thing and then verifying the results is very good advice. As you do a specific task verify each step of that task,then go to the next step.As Randy said know your limitations. Glenn
 
21 - 35 of 35 Posts
Top