Cummins ISM Repower

[Jcparmley]

I have a 89 MCI 102c3 with a 6v92TA with a Allison 740 and a 3.36 rear end.  I have perhaps an opportunity to purchase a salvaged RV with a 450 HP Cummins ISM with a Allison HD4060.  It salvaged RV has the full drive train intact so I can strip everything from the RV to aid in the swap.  This includes the gauges, wiring harness, gas pedal, etc.  What I would like to know is would I need to change the gearing (3.36) in my bus for that powertrain?  Does anyone know what the rpm and speed would be for that engine/Trans combo?  Would this be a good swap?

[luvrbus]

You need to measure the ISM with the 4060 Allison is long combo you may not have enough room and the 3:36 is going to be to tall of a ratio 4:11 is what you need or block out 6th gear

[Jcparmley]

I thought that might be the case with the gearing.  Unfortunately the RV is in another state and I don't have access to measure the drive train.  Perhaps, I can have them measure.  Does anyone have that engine combo in an MCI?

You need to measure the ISM with the 4060 Allison is long combo you may not have enough room and the 3:36 is going to be to tall of a ratio 4:11 is what you need or block out 6th gear

[chessie4905]

Get the specs on length of ism and specs on length of transmission and add them up. Info on both sould be available with some Googling.

[buswarrior]

Nothing is impossible...

The engine room may also have height issues, not insurmountable, but you might not fit it under the rear seat or the fan compartment, and have room to take the cover off to adjust the overhead.

The length issue is likely the bigger challenge.

There are quite a few coaches out there that have had their rear ends loosened off, pulled back, and filler skins hide the evidence. Engine support lengthened, more radiator room, a little more rear bedroom room...

What vintage ISM? Rear gear with a World was often 4.56 before the downspeeding really took hold.

As luvrbus says, you just don't use 6th gear.

If you don't use that drivetrain, someone else on here will pay you a finders fee, fer shure!

Happy coaching!
Buswarrior

[Jcparmley]

It's a 1999 out of a gulfstream tourmaster motorhome.  I was able to easily find the dimensions of the ISM but haven't found the dimensions of the HD4060.  Has anyone swapped their rear gear in a MCI? How much trouble is that?

[chessie4905]

34.1 inches

[blue_goose]

I changed the rear in my 102C3, should have gone lower to about a 4:45.  The gear change was about $2000.00 with parts and labor.  I used a 4:10 and have to be over 63 to get in 6 gear.
Jack

[Jcparmley]

Blue Goose

Do you have that engine and Trans in your coach? 

I changed the rear in my 102C3, should have gone lower to about a 4:45.  The gear change was about $2000.00 with parts and labor.  I used a 4:10 and have to be over 63 to get in 6 gear.
Jack

[Jcparmley]

So Chessie said the HD4060 is 34.1 inches, correct?  The Cummins ISM is 50.78 inches.  That would make the Cummins/Allison combo 84.88 inches total.  So is 84.88 inches to long to work in a MCI 102c3?   I believe from what I found on the internet that the DD 6v92 is 41 inches long and the Allison HT740 is 37.4 inches.  So the engine/Trans that I have currently is 78.4 inches.  That's a difference of 6.48 inches.  Does anyone know if that would work?  I assume I would need to shorten my drive shaft or have another one made but 6.48 inches doesn't seem out of the realm of possibility. 


ote author=chessie4905 link=topic=33833.msg387543#msg387543 date=1552563304]


34.1 inches
[/quote]

[chessie4905]

Check the overall height of the 6-92 compared to the ISM. Make sure it has sufficient overhead space to accomodate the extra length.

[buswarrior]

Driveshaft on the stock install is already perilously short.

MCI took full advantage of the small size of the Detroit V motors, both height and length.

Dramatic changes were required to put inline 6 cylinder engines into the MCI chassis.

Note the significant difference in the distance from drive axle to rear bumper between the different generations.

Nothing stopping you from making it work. Consult with the U-joint manufacturer tech people on the limits, and extend the rear to get the rest?

Have you read about the shorter Series 50 successes of other busnuts?

Happy coaching
Buswarrior

[Jcparmley]

It looks like the height of the 6v92 is around 50 inches and the Cummins ISM is 45 inches.  I am not sure about the height of the ISM with jakes.  I know when Brian D did his repower he had to adapt the bedroom floor to make his ISM with jakes fit.  However, Brian has a MCI9.  I am not sure if the MCI9 has a lower floor than the MCI102c3.

96uote author=chessie4905 link=topic=33833.msg387571#msg387571 date=1552693836]
Check the overall height of the 6-92 compared to the ISM. Make sure it has sufficient overhead space to accomodate the extra length.
[/quote]

[Jcparmley]

I haven't looked into a series 50.  Would that be an easier swap?  I heard they have vibration issues.

 

Driveshaft on the stock install is already perilously short.

MCI took full advantage of the small size of the Detroit V motors, both height and length.

Dramatic changes were required to put inline 6 cylinder engines into the MCI chassis.

Note the significant difference in the distance from drive axle to rear bumper between the different generations.

Nothing stopping you from making it work. Consult with the U-joint manufacturer tech people on the limits, and extend the rear to get the rest?

Have you read about the shorter Series 50 successes of other busnuts?

Happy coaching
Buswarrior

[Jcparmley]

I just read that the 6v92TA is 44 inches long not 41 inches.  So that would make the 6v92TA/HD740 combo 81.4 inches.  That would be a difference of 3.48 inches.  That sounds better to me.  I wonder why the 6v92ta is longer.