MCI 5C with 6V71 Need Info

[davidr]

I'm looking to buy a 35' MC5C but it's in California and I'm in Texas.  It has a (supposedly) rebuilt engine without any documentation.  It's got a 6V71 with an Allison 644.  A few years back I had a 5A with an 871.  Never driven a 6V with an auto.  How's the 671 with an auto tranny.  I'm not looking for speed, just reliability, cool running and most important gas mileage.  I got 7-8 mpg with the 871, any real world driving estimates for this busses set up?  Any info about how to confirm a rebuild.  If i fly out to look at it, I'll get an oil test and have somebody look at it.  any good mechanics (besides S&S) in the southern california area.  My local bus guy says the allison 745 was the best made, how does the 644 compare and will the 745 fit in this bus?
thanks for any info

[TomC]

The 644 will live alright behind the 6V-71.  At best the 6V-71 will put out 228hp and 600lb/ft torque with N65 injectors compared to the 8V-71 with N65's at 304hp and 800lb/ft torque.  Your performance will be leisurely, but reliable.  Your mileage will be about the same 7-9 since the 6V will be working hard all the time compared to the 8V being a little more relaxed with its' better power.  You could either turbocharge the 6V-71 with 80 injectors that will give you 300hp and 900lb/ft torque that will be close to the 8V-71 performance.  Or you could just plainly swap out for a 6V-92TA that is virtually identical on the outside to the 6V-71 for 350hp and 1050lb/ft torque.  They did make a 6V-92N with no turbocharger, but very rare.  That was 275hp and 750lb/ft torque.  Good Luck, TomC

[JackConrad]

   The 600 series transmissions are "medium duty", the 700 series are "heavy duty".  I know several people that have the 6V71/644 combination. I have not heard of any problems with this combination.  As far as overheating issues, if this bus was a Saudi model, it will have oversize radiators. Saudi models came with 2 doors (transit style) and a "double roof".  Jack

[luvrbus]

David, you can use the 700 series Allision with a V6 DD in a 5 but you are limted to the 500 or 600 series with the V8 DD   good luck

[lostagain]

I used to drive MC5 A's, B's and C's in the '70's for Brewster's (Banff, AB). Great coaches, very handy in tight spots. The A's and B's were sport cars with lots of power to weight ratio. The C's with 6V71/auto felt underpowered by comparison. Quite slow. It might be allright in a conversion if you don't mind a leisurely pace. I'd have to drive one again to see what it feels like. Like Tom says you could turbo the 6V71. I did that to my 4-71: well worth it, big difference. If you found one with a 8V71 in good shape, you could turbo that...

JC

[tekebird]

not all the saudi units had the center door, although all did have the desert roof

you should be able to determine a rebuild by having a look at the cylinders.  ( a well done rebuild will look like a new engine too...most people go to the trouble of painting them when they are out)

[jjrbus]

I have a 79 5C Saudi model. 6V71 with the 644. I thought the perfomance was terrible, till I rode in other buses the 671 with the 644 is not bad when compared.
Changeing the tranny would be a waste of time and money, The 745 might fit, but the drive shaft would be very short. The 644 has been mated up to 8V71s and 6V92's I have never heard anything negative about this tranny. It is also used in heavy duty trucks, where it will get much more abuse that it will ever get in a conversion.  
I also have a 50,000 mile rebuild, I bought the bus from a dealer who was selling it for a charter company. The documentation was lost in transferring. When I bought the bus the motor and transmission had 15K on the rebuild. The paint was fresh and obviousely done outside the bus. The mechanic that I became friends with assured me that the bus had an out of frame engin and tranny rebuild.  Some years have passed and the motor looks like it has a million hard mailes on it!!!!
What I have noticed on my "fresh" rebuild is that when I start it. The motor does not spin, crank, turn over. I push the button and it starts instantly. Even when cold, touch the start button it starts. I have noticed on tired engins that they crank a bit befor starting.
The Saudi model has oversized radiators (I belive they are MCI9 with 8V71 radiators) and no shutters. My bus runs very cool. I went up that big grade in California  Baker? cant remember the name. in the summer and the temp gauge barely moved.  I actually changed the thermostats to try and raise the temp a bit.
Fuel milage, I dont know, I do not care, I do not want to know. I have documented every fuel purchase I have made. I never figure them out.  I'm sure if I knew what it got I would never drive it again!!!!  When asked I tell people 15 MPG.  That is 9 on the hiway 6 in the city, 9+6 = 15 right???
Take your time buying, I am looking for a house and when I find one I will sell mine, I'm on the west coast of Florida so will be short trip for you.
                                                      HTH Jim

[mccarlk]

i just ordered a bunch of parts to go over my 644 in my 8v71 ta mci5a , and lots off the internal parts interchange with the 7oo series, ken