Repowering a MCI 9 is not for the faint of heart

RickB · May 05, 2019, 05:22:33 AM

Hey all,

The 8V71 is out on a mobile stand and the 8v92 is in... Removing the 8V92 was the easiest part of the job and installing it in my bus was by far the hardest part. I wouldn't do it again at my age (57) and I am seriously worse for wear physically from this. Have a couple remaining issues... The shifter linkage from my previous 754 Allison seems like it's going to need a fair amount of adjusting to get it to work with the 740 I got with the 8V92. Also, I know where the two small wires hook up to the back of my alternator but I don't know which is which. My air connections to the engine shutoff and governor are different because I had jakes and I have decided not to add them to my new drivetrain.

So, it's in. It's not running yet and I would never do it again... Too much work and too dangerous.

Rick

bevans6 · May 05, 2019, 06:27:00 AM

Good that you got it in OK. I might have had to put my 8V-71T in and out of my MC-5C a dozen times when I was installing my MT647. Measuring for angles, head room clearance (an issue you don't have so much with the MC-9), driveshaft angle and length, shims, cutting the cradle for angle, shifter linkage, air governor install, rear plumbing connections. I had it sat on a pallet jack and if the floor was clean I could just roll it in and drop it down in five minutes. Then I would rest for five or ten minutes - 3,000 lbs on a pallet jack is heavy, even on smooth concrete. Did you get your driveshaft sorted?

Edit - if you are dumping the Jakes, you only need one skinner valve and the No-Fuel air cylinder, the other two air cylinders and their skinner can be removed/not installed. The two wires are the F1 (field) wire and the R (relay) wire. The F1 wire is 12 gauge and might have a yellow tracer, the relay wire is 16 gauge and should be black. Easy to tell apart, and the alternator has cast in markings. If you have a buzzer, the F1 wire goes to stud 48 in the rear panel, the relay goes to stud 33 and terminal 2 of the Blower Disharge relay.

Edit again - I assumed (bad on me) that you had the fast idle jake system on your old engine, because you mentioned that it has an air connection. Obviously it's the fast idle part that is air controlled, the Jake is purely electrical. Does your new engine have fast idle?

gumpy · May 05, 2019, 07:38:47 PM

Some day you'll learn to listen to those wise individuals who told you your old 8V71 was a good strong engine and you should learn to drive it and enjoy it rather than waste time and money on a repower.

RickB · May 06, 2019, 05:48:20 AM

Bevan's, thanks for the info. It is very helpful. I have two unresolved issues moving forward. The throttle linkage and the transmission linkage, both mine are short by about an inch. How does one adjust the throttle linkage? So I went from jakes to non jakes as well are there only two air lines running to the engine in total? I'm guessing the hi idle is on the left side of the chassis looking forward from the rear of the bus and the fuel shutoff is on the right correct?

RickB · May 06, 2019, 06:07:52 AM

Gumpmeister, it was either repower or sell the bus. If you drove a non-turbo'd engine in the mountains you'd see it's too freaking dangerous. My son and I almost got in a head on collision because an impatient millennial passed us on a double yellow. I swore I'd never do mountains again without a turbo. I figure in the black hills I'm down to 175 hp at the peaks and in Colorado I'd be down to 100 hp with my 8v71. Pretty tough running up a mountain with 32,000 lbs with a 100 hp.

Fred Mc · May 06, 2019, 12:18:17 PM

I have an 8/71 that I have had forc30 years and have driven in "real" mountains on the west coast of Canada and the US including a trip to Denver. Going up can be slow yes. It's coming down that is more concerning to me. Mind you, I have a gm4106 -the sports car of busses so maybe that's the difference. 😁😁😁

bevans6 · May 06, 2019, 12:25:27 PM

Rick, as far as the throttle and trans linkages are concerned, mine are both cables and i just adjusted the routing of the cable. I would check that you have the engine in far enough on the slides, the governor should be in the same location as the one you took out if the engine is slid in all the way. As far as the air lines are concerned, I still don't understand if you have fast idle or not. If you have fast idle, that air cylinder sticks out of the vertical left hand (driver's side) wall of the governor, in the buffer screw location. It replaces the stock buffer screw. It will have one air line going to it, and a second air line going to an air cylinder that locks the throttle lever in idle. You must have both air cylinders hooked up and working, they both run to the same skinner valve. The engine stop lever is on top of the governor, one of two levers, it's the left hand-most one, and it has an air cylinder that presses it into the no-fuel position. It goes to the second of the skinner valves.

On my MC5C there is a notch on the right hand rail that the AC belts go through. The engine cradle has to be flush with the edge of that notch. Picture:

TomC · May 06, 2019, 10:13:40 PM

Why don't you run the HT754CR-it is rated for the 8V-92TA. The 8V-92 is virtually the same dimensions as the 8V-71, except for the additional vibration dampner on the front of the engine. Good Luck, TomC

RickB · May 07, 2019, 03:32:23 AM

Bevans,
I'm hoping the since the "T" motor mount fits in the slot on my bus that I have the engine all the way in. The plate on top of the governor on the 92 is different and so I'm going to try retrofitting the plate off my 71 in hopes that it works. The transmission linkage is a bit wonky too... maybe because I'm going from a 754 to a 740 and the lengths are different.

On a side note, got it running last night. Ran it for a couple minutes. Runs good. I have the intake of the turbo open because I'm still working out the routing of some air lines so I didn't run it long.

TomC, I really wanted to keep the drivetrain intact and my 2nd gear start 754 slipped a bit at takeoff years ago so I was running straight 30 weight engine oil in it. It never slipped again after I made that change but I'm doubling my horsepower so I decided to stay with the 740.

When I figure out both linkages, work through a couple air line issues and route the intake plumbing I'll be ready for a test run

Rick

bevans6 · May 07, 2019, 04:03:10 AM

If you mean that funny aluminium top plate that MCI installed all the air cylinders and linkage mounts on, I would swap it over too. I did on my engine repower, and I think the basic governor is the same on both of your engines. I would also swap over the MCI throttle lever, it has the right connections for the pull cable for the throttle and the push cable for the modulator.

luvrbus · May 07, 2019, 07:24:49 AM

Watch changing the cover on the governor the 8v92 uses a starting aid the cover needs to match they can have external or internal starting aid if not careful you can have your handful trying to shut it off

bevans6 · May 07, 2019, 09:47:20 AM

My 8V-71T has an external starting aid adjustment, so the plate over the actual governor top didn't affect it at all. I think we are talking about the add-on, kind of home made looking 1/4" thick aluminium plate that MCI used to bolt the cables and air cylinders to, not the actual top cover of the governor.

Question - the HT754 would have a similar modulator and cable that should work on his HT 740, wouldn't it? The one you sent me I had to take apart and swap it to be a push type to work with my MCI throttle lever setup, and I had to make up a way to bolt the cable housing to that plate. Based on remembering that, I thought it worthwhile to mention that the modulator cable can be either a pull type or a push type, and you need to make sure it matches the way the throttle lever is acting on it.