Hello again, at what air pressure does the fast idle kick in on a 8v71t and at what pressure does the air dump. when I start the engine the air builds up to about 130 lbs really fast and stays there but the fast idle doesn't kick in and the air never dumps. I bought the bus about two months ago and haven't had time to check everything out maybe I should check the gages. I have had two MCI s one with a 8v71 an the next one I had was a 6v92t that was ten years ago an I have forgot most what I knew about the engines.. Thanks again for the help Richard "Happy Bussing"
If you have a fast idle air cylinder, it is pressurized by the auxiliary air system, which gets air after the main tank has reached around 60 psi. So it can operate sometime after you see 60 - 70 psi on the dash gauge. It is operated by the dash switch which controls a Skinner valve on the rear engine wall just forward of the rear control switch box. There are two Skinner valves there - one controls the shut down air cylinder and one controls fast idle. There are actually two air cylinders controlled by the fast idle Skinner valve, the other one locks the main speed control lever to off, so that the engine cannot come off the idle control inside the governor.
8V-71T in an MC9 (just guessing here, you don't say what bus you have but your name implies MC-9) would be a transplant, probably a truck or military engine. They often did not come with fast idle, so your engine could well not have it. Your air governor should be set to tell the compressor to cut in at 95 psi and to cut out at 120 psi, that is the normal range for MCI's. Your air dryer should purge when the air governor switches to cut out.
Brian
Hello, Brian I forgot to say about the bus, I had a MC9 and sold it now I have a 1965 01 Eagle. I understand now about the fast idle the 8v71T was a government rebuild from Redstone Arsenal, Al. The turbo Is mounted on the side of the engine the amazing thing to me is the way it was packed. It came in a crate an inside the crate was a sealed bubble and inside the bubble was the engine the bubble was pressurized with some king of gas , and I was told it was for a tank 405 HP Thanks again Richard PS the pressure holds about 130 lbs
Sounds like the same engine I have, or started my engine conversion with, a 405 hp ex-NATO military engine. Mine did not have a fast idle installed when in military configuration, I installed the one from the MCI engine when I did the conversion. At 405 HP gross, it will have N-80 injectors and smoke like a freight train at over 3/4 throttle under load. It will climb hills with the big boys though.
Brian
The last model of 8V-71TA from Detroit had N80 injectors producing 400hp @ 1200lb/ft torque. If you're smoking at full throttle, you don't have the correct turbo. On those tank engines, the turbo was an old style and gigantic. There are newer turbo's that will put out the boost so the 8V-71 should not smoke. Mine with 7G75 injectors smokes a bit on acceleration, but climbing a hill all I see is heat coming out of the exhaust pipe (I have an up exhaust I can see from the driver's seat). I had a truck driver friend that put 90's in his 8V-71 and changed the turbo. Ran like a scared deer. Good Luck, TomC
Tom, that is exactly what Don Fairchild told me at the time. Just being Scottish and all I didn't see buying a new turbo to replace a perfectly good turbo, so I just drove so I didn't get smoke. Now I have N75's in and a lot less smoke.
Brian
Not all the military engines use a fast idle cylinder on the buffer some use a cylinder made into the cover for the adjustments of the idle and speed it works from air and just pulls on the idle adjustment screw, that type requires no holding cylinder. The newer fire trucks used that type with the 8V92
My military 8V-71T just had a normal buffer screw, was the point I was completely failing to make. Sorry about that. ;D I took the fast idle setup off my MCI engine and transfered it to the military engine.
Brian
Here is a picture of the engine I have except mine was painted black "why black?"
picture of bus before I start upgrade conversion, now got to figure out how to start my project page
It's really pretty easy to start a Project page for your Eagle. Just follow the simple instructions as outlined below.
"This section of the forum is for you to be able to share the stories and photos of your bus.
For it to be easy for people to find it, please use one thread per bus and for the subject line put the bus year, brand & model, and if you like, your name for it. For example:
1982 MCI MC-9 "John's Dream"
It doesn't have to be chronological, but if you do choose to organize your thread that way it will be easier for your fans to follow your progress.
Readers: As a courtesy to the OP of the thread, please practice extra care not to drift the thread. Keep replies specific to the bus and projects described in the thread. If you have a drifting side note, perhaps post it on the All Topics board and post a link over to the Project thread it is about."
BTW, very nice looking 01! What is the VIN#? Us 01 owners have to stick together! ;)
Same specification engine as mine but with the side mount turbo. That would have been in an M109 self-propelled 155mm howitzer.
https://en.wikipedia.org/wiki/M109_howitzer
Brian
Quote from: bevans6 on October 08, 2015, 04:16:06 AM
8V-71T in an MC9 (just guessing here, you don't say what bus you have but your name implies MC-9) would be a transplant, probably a truck or military engine.
Brian -The 8V71T was an option for the MC-9. The charter bus outfit I worked for back in the '80's had two in the fleet that they'd ordered new, both with the HT-754 Allison, too. IIRC, they were 1981s, tuned to 350hp. Those were really sweet coaches - especially climbing all the various 6% grades we have in this area of CA.
Not sure what happened to one of them, but the other is still earning it's keep for Fresno Pacific University (private), along with a newer D series.
FWIW & HTH. . .
;)
Don't know if is the same bus or not RJ but there is a MCI 9 in Lake Havasu that has the same power train as you mention
My 75 mc8 only whistles when u flick the fast idle switch and never speeds up as the cold weather gets closer I'd like it to work but idk