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Author Topic: Shoving a 6V92 into a 6V71 hole  (Read 4723 times)
Craig R
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« on: July 29, 2006, 09:56:10 AM »

I have an MC5c with a DD 6V71 engine and an Allison MT644 automatic transmission. In my idle moments I think about repower. Folks talk about the 6V92 being a simple “bolt-in” replacement because of virtually identical dimensions  but then other people describe turbocharger replumbing necessitated by minimal vertical clearance in the engine compartment.

If my engine were to seize up tomorrow, is there a 6V92 with which I could replace it as simply as with a 6V71? For perspective, would even another 6V71 be a simple “bolt-in” replacement?

When I look around for available engines I see engines out of transits & Prevosts & Neoplans & skoolies & bigger (newer) MCIs, I see stationary engines & marine engines and engines from COEs & fire equipment & heavy machinery, I see DDECs and non-DDECs, I see T’s & TA’s & TT’s & TTA’s –and the very occasional naturally aspirated 6V92. I forgot lefties and righties!

What’s a boy to do? Will one from an MCI slide into the box with less fanfare than one from a different make of bus? From a bus versus from a different vehicle? Versus marine? Versus stationary?

Would using a naturally aspirated 92 avoid the need to reposition the turbo and also decrease the oft lamented problem of insufficient engine cooling capacity encountered in such a repower?

Should one keep the transmission that’s currently in the bus or use the one that’s often hanging off the repower? How big a problem is bell housing mismatch? Weight? Mounting points? Driveshaft length and angle? Shifter compatibility (hey, that brings up the issue of engine controls too!)?  How about horsepower and torque rating?

Is there a handy reference somewhere out there that addresses these matters?
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Len Silva
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« Reply #1 on: July 29, 2006, 10:14:04 AM »

I can remember many years ago, probably the late sixty's (that's a feat in itself) driving through Delaware or South Jersey, I drove past a shop that said:

Sam's Welding and Truck Repair
We Adapt Anything to Anything
[/b][/size]

That's the guy you need to see!  Grin

Len
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NCbob
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« Reply #2 on: July 29, 2006, 11:47:31 AM »

Craig, I cannont answer many of your questions but I might be able to throw some light on others.  I own an MC5A and here's some of the items I see.  First, you have a drop box between the transmission and the drive axle.  That is going to limit your selection of transmissions.  As far as I know there's only one automatic transmission that will work with the 71 series and whether or not it's rated for the higher HP and Torque of a 92 Series...I can't answer.

Another item is the blowers.  Since the MC7 thru 9's have a higher roofline than the 5's the blowers are higher allowing for more room for turbo's etc.  If the 92 Profile is much higher than the 71 profile you could be in trouble there.  Another question is...will the engine stringers handle the extra weight?  Dunno!

Your 5 must be worth putting all that additional HP and money in but the question is....will you be able to get it back out of the investment?  It's one thing to get out there and run with the big dogs but I don't believe it's worth the cost.  That's an opinion.
Too, that 92 is going to create one helluva lot more heat and I'd guess the current radiator and fan setup might be a source of a problem you'd wish you didn't have.

The 5's were designed for the 71 series engines...Be sure you get answers to all your questions before you proceed.  I wouldn't want to see you in the list of 'former' bus owners.

Bob
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TomC
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« Reply #3 on: July 29, 2006, 03:06:40 PM »

The ONLY exact change out would be the 6V-92N, of which there are few around. You'll go from 238hp and 600lb/ft torque to about 275hp with about 750lb/ft torque.  An improvement, but the 6V-92TA with 350hp and 1050lb/ft torque would be better with the HT740 transmission.  Course, you'd have to increase cooling, plumb in the turbo and exhaust, contend with the bigger transmission.  You could also built your 6V-71 into a turbo also, then it would be about on par with an 8V-71N's power.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
christopher
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« Reply #4 on: July 29, 2006, 03:56:27 PM »

email me again w/your# and i will call you
chris
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pvcces
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« Reply #5 on: July 29, 2006, 09:41:35 PM »

And while you're thinking about the possibilities, you might consider the 8V71N. I seem to recall that the MC-5s had them from the factory. I don't know how serious the transmission constraints would be, but the engine should be available cheap and there should be enough MC-5s around with that configuration to answer your questions.

For what it's worth.

Tom Caffrey
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Tom Caffrey PD4106-2576
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Stan
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« Reply #6 on: July 30, 2006, 04:48:40 AM »

The factory options were 8V71 with four speed stick or 6V71 with 740 Allison. There is not enough length for a 8V71 with a 740. However many updates have been done with the 8V71 and 600 series transmission.  Since Craig already has a 644, he could tie a 8V71 onto it. He could push the 8V71 to whatever HP he wanted with turbos.
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TomC
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« Reply #7 on: July 30, 2006, 09:17:18 AM »

Stan- the MT644 behind the 8V-71N is at its' limit.  To go to a turbo a HT740 should be used for reliable long lived service.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Stan
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« Reply #8 on: July 30, 2006, 10:36:31 AM »

Tom: I don't remember all the numbers but I think the 644 was rated for 70k pounds GVW but the limiting factor was torque. It was a common transmission in gravel trucks pulling 40k out of the pit so it would last a long time in a highway coach. As with all components, it depends on how you drive. Some drivers can wreck anything. Long life becomes a relative thing when few conversions ever get driven more than 50k miles by the original owner.
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jjrbus
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« Reply #9 on: July 31, 2006, 06:14:42 PM »

If your 5C is a Saudi bus, check your radiators. The Saudi models used the radiators from I belive the MCI 7 and should be sufficent for the 6V92. Also the 644 is a keeper with the 6V92 or the 8V71.
 I've got the 6V71 with 644 and it is one slow bus, very frustrating going up hills in WVa g oing 30 with everybody else going by you at 70. I've often thought about this swap but it is just not economicaly fesible. I can pick up a motor for $2/6000 and then maybe spend that much again on parts and accesories. Cannot possible be worth it.
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Rodsmc5c
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« Reply #10 on: August 06, 2006, 06:36:47 PM »

hi
   I'm picking up my 79 mci5c with a 671 tomorrow. is this engine/auto trans that big a problem?  i mean performance wise like down the highway. This is my first experience at driveing a bus, should be interesting huh.
                                                         thanks  Rod
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RJ
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« Reply #11 on: August 06, 2006, 06:57:28 PM »

Rod -  I've said it before, and I'll say it again:

When driving a bus, and I don't care if it's a skoolie, transit, or highway model, with 150 or 500 horsepower, you have to keep in mind the children's fable of the Tortoise and the Hare.

Expect to drive it like a Hare, and you'll be frustrated and disappointed.   Angry Angry Angry

Drive it like a tortoise, and you'll be a happy camper.   Smiley Smiley Smiley

This from someone with 25+ years in the bus industry. . .

If you've never driven a bus before, these links should be helpful:

http://www.busnut.com/bbs/messages/11/14184.html?1154188465

http://www.busnut.com/artrjl2.html

http://www.busnut.com/artrjl1.html

Good Luck, and enjoy your new toy!

FWIW. . .
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RJ Long
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« Reply #12 on: August 07, 2006, 02:30:45 PM »

If you can do the work your self. Go with the 6V92Ta and the 644 transmison. You will need to install a side mount torbo in your coach. But I have seen several that way It will cost you about $1200 for the parts. As for the 644. I no it is not rated for that amount of power. But I have a friend that has a MCI 7 that has that transmision in it and it has been in it for 12 years. It has never given any problems. !000s of miles. If I had a 5 that is how i would fix it. I also no of a 5 that has that same transmison and a 6V92TA that they full time in it and they have never had any trouble with it. Fred
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Ray Powell
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« Reply #13 on: December 27, 2006, 09:33:51 PM »

Better late than never!! I am installing a 6V92T with a MT644 in a 5C. My hang up is finding the crankshaft to flexplate adapter. The Allison part # is 23046435 but it's not coming up. Maybe thats wrong number. Anyway I'm looking for the adapter.
C Ray
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Stan
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« Reply #14 on: December 28, 2006, 06:13:39 AM »

Ray: A 6-92T is going to be pretty high HP for a MT644.
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