| Author | Message | ||
| Moe Hollow (Moehollow)
Registered Member Username: Moehollow Post Number: 25 Registered: 12-2007 Posted From: 68.183.235.126 Rating: N/A |
The emergency shut down on my MC5a/8v71 was non-functional when I bought it. Today, I traced out the wiring thanks to the schematics since my tone generator did not seem to be able to do the job (maybe something is wrong with it)and removed, cleaning up and reinstalled the solenoid. So now I have a convenient dash button for emergencies. I tried to test out how well it worked by starting the engine and hitting the button. The solenoid worked, and the valve sprung closed as it should. However, the engine did not shut down. The engine obviously was impaired but was still getting enough air to sputter along. My speculation is that, although it does not seal well enough to shut down at idle, it would do so if the engine was racing. Is this how it is supposed to work? Also, are there negatives to shutting the engine down in this way? | ||
| John and Barb Tesser (Bigrigger)
Registered Member Username: Bigrigger Post Number: 55 Registered: 9-2007 Posted From: 24.197.246.104  Rating: N/A |
I am not sure how the shut off works on a bus, but when I had dd 8v71 in a truck, the only downside to using it was you had to jack the cab up and reset the valve manually. It didn't cause any harm to the engines, all its doing is shutting the air off (at least in the case of a truck). | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1187 Registered: 12-2000 Posted From: 76.68.123.18  Rating: N/A |
Hello Moe. Your emergency shut off is working fine. Its job is to obstruct the airflow to the engine. Some will stall the motor out completely, some will do as yours does, and let it chug along with great clouds of smoke. It all depends on how well the flap inside the intake fits against the screen above the blower. As you already know, this feature is there for an alert driver to prevent the engine from destroying itself, if some part of the fuel delivery system fails and allows too much fuel into the engine. Stuck injector, broken return spring in the fuel rack, binding rods, broken pins in the rod ends, broken/seized bits in the engine governor, etc. Reusing parts beyond their useful service life is a common culprit in these misadventures, and busnuts are unwittingly on the receiving end of many of these shoddy practices. Only those who fail to maintain their fuel delivery system will have a need for the emergency stop, and in that case, it probably won't work either. Good job, getting it functioning again! happy coaching! buswarrior | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 226 Registered: 7-2006 Posted From: 4.240.213.164 Rating: N/A |
Excellent question, Moe...important and very pertinent. Great answer BW...and thanx for a detailed, clear explanation that, theoretically at least, involves all of us. What a great board. Thanx, Ian!!!  RCB | ||
| Moe Hollow (Moehollow)
Registered Member Username: Moehollow Post Number: 26 Registered: 12-2007 Posted From: 68.183.235.176 Rating: N/A |
Thanks for the answer. Now that the emergency shut down is working, I will test it periodically to make sure it keeps working. I actually had an incident when I reinstalled the fast idle cylinder incorrectly, putting the pin in first and then screwing the cylinder in, that caused the pin to jam into the governor housing. When I started the engine, it went wild. Since there was no emergency shut down, it kept going until there was enough air for the fuel shut off to work. It may have run like that for 20-30 seconds, but it sure seemed like a long time to me. | ||
| AL (Proudeagle10)
Registered Member Username: Proudeagle10 Post Number: 54 Registered: 4-2005 Posted From: 75.104.192.37 Rating: N/A |
An idea I have been thinking about, but don't know if it's safe or even practical. I have been thinking of installing a fuel shut off solenoid just aft of the fuel fillter and prior to the engine. I would install a normally open, energize close solenoid. This solenoid when energize would shut the fuel to the engine. Encase of a runway engine. AL | ||
| Bruce Henderson (Oonrahnjay)
Registered Member Username: Oonrahnjay Post Number: 214 Registered: 8-2004 Posted From: 68.33.63.53  Rating: N/A |
Al wrote "An idea I have been thinking about, but don't know if it's safe or even practical. I have been thinking of installing a fuel shut off solenoid just aft of the fuel fillter and prior to the engine. I would install a normally open, energize close solenoid. This solenoid when energize would shut the fuel to the engine. Encase of a runway engine." __. That's a good idea, Al, but some runaways come from other sources (blown gaskets, cracked parts, broken lines, etc.) that allow engine oil into the intake (we won't even talk about "crankcase ventilation systems" ... too stupid to even consider). I like the idea of *both* a fuel shutoff solenoid (my bus has an electric one standard) AND an emergency air shutoff. | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 587 Registered: 11-2005 Posted From: 208.54.200.239  Rating: N/A |
Moe, I would recommend testing your emerg shutoff with the engine not running. This is just as good a test as with it running and there is no chance of damaging the air box or blower gaskets. | ||
| john w. roan (Chessie4905)
Registered Member Username: Chessie4905 Post Number: 869 Registered: 10-2003 Posted From: 71.58.48.5  Rating: N/A |
It would be nice if you could reset it from the driver's seat- be great to get tailgaters to back off. | ||
| Moe Hollow (Moehollow)
Registered Member Username: Moehollow Post Number: 27 Registered: 12-2007 Posted From: 68.183.235.176 Rating: N/A |
Gus, I did test it that way first. I can actually hear it distantly click when I hit the button. However, with so many things having been altered or removed over the the 42 years of this buses life, I felt I had to see it in action to know what I had. What if there were no butterfly in the pipe. | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 138 Registered: 3-2006 Posted From: 209.50.74.42 Rating: N/A |
The best way to test the Emergency shut down is at idle. If you activate it at high rpms you stand a chance of destroying the seals on the blower. The high suction suddenly being shut off by the flap above the blower will cause the engine to try to suck air from anywhere it can. If the flap closes at idle it will cause the engine to blow a lot of black smoke without any damage. Just a word of warning. | ||
| Gus Causbie (Gusc)
Registered Member Username: Gusc Post Number: 588 Registered: 11-2005 Posted From: 208.54.200.143 Rating: N/A |
Moe, A good point, never thought about a missing flapper. Now that you know the flapper is there you can test it with the engine off. One other good idea is to put a guard on the panel switch. It could ruin your whole day to hit it by accident while at speed! Little kids love switches too. Mine is next to the reverse switch so it would be real easy to hit by mistake. (Message edited by gusc on February 17, 2008) | ||
| Moe Hollow (Moehollow)
Registered Member Username: Moehollow Post Number: 30 Registered: 12-2007 Posted From: 68.183.235.224 Rating: N/A |
Yes, I think you are right about protecting the button. It looks so harmless that even I might be tempted to push it at some point. | ||
| Buswarrior (Buswarrior)
Registered Member Username: Buswarrior Post Number: 1190 Registered: 12-2000 Posted From: 76.68.123.43 Rating: N/A |
Stock install has one of those red plastic switch guards over the emerg stop switch. Yes, get a cover for it! happy coaching! buswarrior |