Update on MT-647 - MC-5C install

[bevans6]

After a long winter's break, I am working on this again.  I am adapting and installing an Allison MT-647 behind (in front of?) the turbo 8V-71 in my 1980 MC-5C.  I am at the fettling of install stage, and being retired and quite lazy taking my time with it.  I have successfully adapted my Cummins ring gear onto my modified Allison SAE 1 Detroit flex plate, wherein I cut off the SAE 1 ring gear, trimmed the flex plate to fit the ring gear, and made up a crankshaft adaptor to bolt the whole mess onto the crank shaft.  Critical clearance was to the pinion of the starter motor.  The Cummins ring gear is one tooth larger in diameter than the Detroit flywheel ring gear, so I modified the nose of the starter motor to move it out radially about .100".  Next, I measured the clearance from flex plate to transmission mounting flange, and made up some shims to move the transmission back for perfect spacing.  I needed 1/4", I used two 1/8" spacers, one between bellhousing and adaptor and one between adaptor and transmission.  That left enough register engagement so alignment is ensured.  In the process of installing the transmission onto the engine the torque converter moved forward an inch or so - I pushed it back and and am really hoping that I didn't damage the front seal of the transmission.  I guess I will be using the bright red transmission fluid so I can tell if it leaks.

So I rolled the engine complete with transmission in and set it in place.  My driveshaft (made of unobtanium parts to judge by how much they cost and how hard they were to find) is 16.5" fully collapsed between flange (on the drop box end) and yoke center (transmission end).  I have, with the engine in the stock position, 16 5/8" space, so 1/8" of wiggle room on the driveshaft length.  That puts the oil pan of the transmission only 1/8" away from the cross-member as well, so I will probably shift the engine 1/4" forward of the stock location.  I installed the driveshaft and jacked the axle up to confirm what I already knew - the driveshaft will hit the axle at full droop.  Now, I am finessing the angle of the dangle.  I will be lowering front of the engine by cutting the engine cradle mounts down and re-welding 1/4" - 3/8" lower, and I will be shimming the rear of the engine at the motor mounts, the idea being to create an angle that raises the rear of the transmission by about 1"  without raising the actual engine all that much (no headroom in the engine bay of a MC-5C).  At the same time I will be working out how to mount the oil cooler - probably on the floor of the passenger side engine bay, kind of where the door opens and the air conditioning pump used to be.  Still working that out, but grinding wheels are in stock...

Goal is to go for a nice run later in the summer, so working on at a steady pace, keeping up with all the other chores no one else seems to do around here...   

[lostagain]

Sounds like a great project. Wrenching on these old buses is as satisfying as driving them and camping with them. You will savor the fruits of your labor later when you drive it. How does all that moving the engine around affect the pulley alignment for the belt. Or do you think there is enough adjustment to make up for it?

JC

[Lin]

We needed a longer belt.

[bevans6]

I am quite worried about needing a longer belt.  My blower drive is stock, with the air cylinder tension setup, and it moves up and down about an inch, it's designed so that if you dump the air to the tension cylinder you can pull the blower drive down and put a lot of slack on the belt to easily change it.  I am going to try to work out how much I can lower the front of the engine within the parameters of that scope of adjustment, so I can use the same belt.  It's not aligned all that well stock, so moving the lower pulley 1/4" won't make much of a difference, if any. 

Brian

[bevans6]

How interesting!  My belt is a MCI part number, it would seem, a Dayco 8C-27-5.  It comes up in MCI parts lists, but dayco doesn't seem to know about it.  I recall when I bought it, it had to come from MCI.  It crosses over to a Gates CX-105, and is 109" around.  They list a Gates CX106, which is 110" around, so perhaps a useful option.

[lostagain]

While you are at it, ha ha, you could replace the pulley on the blower drive with a smaller one to spin the squirrel cages faster. That is what I have. It is 8".

JC

[RJ]

Brian -

Doug Pierre has a 5C that he stuffed a 6V92T/V730 combo into the engine compartment, which is the same powertrain JC has.

His solution to the top-mounted turbo was to raise the blower floor.  His squirrel cage housings miss the coolant surge tank by 1/8" - you can't even get a finger between them.

He also cut the discharge opening of the blowers to 14"x14" - he said that that modification really made a big difference.

My engine swap is on hold for the time being. . .

FWIW & HTH. . .

[luvrbus]

Brian -

Doug Pierre has a 5C that he stuffed a 6V92T/V730 combo into the engine compartment, which is the same powertrain JC has.

His solution to the top-mounted turbo was to raise the blower floor.  His squirrel cage housings miss the coolant surge tank by 1/8" - you can't even get a finger between them.

He also cut the discharge opening of the blowers to 14"x14" - he said that that modification really made a big difference.

My engine swap is on hold for the time being. . .

How did he make a V730 work on a T drive MCI 5 inquiring minds would like to know


FWIW & HTH. . .

[luvrbus]

That big turbo on a military engine you would need to remove the blowers  those things are huge and lazy,I need to send Brian 5 or 6 the turbos I have and let him play around a bit

[bevans6]

I would love a smaller turbo!  This one is huge, and I am going to have to move things for it to fit this time...

Brian

[lostagain]

RJ, my trans is a HT740. You knew that, but forgot and typed V730. Isn't the aging brain a treat!

JC

[lostagain]

Sorry double post somehow.

[TomC]

With the hot rod tank military 8V-71 turbo, you'll have to watch the acceleration torque to the transmission. The only time you should do full throttle is after the torque converter is locked up and in a gear. If the transmission is going to shift, lift your foot and let the transmission get into the next gear. Typically, once the transmission is set in gear, you can then floor it again. Or-lower the injectors back to 7G65's. You'll still have 325hp and 975lb/ft torque. Good Luck, TomC

[bevans6]

Tom, I already de-tuned it down to N75's.  From what I have read, that puts me at the top of the window for torque on the 647 at peak torque, but I take your advice to back off when shifting...  I rarely have to use full throttle anyway.  I am below the torque rating at 2200 rpm, which is the full throttle shift setting (if I understand what the tech who set it up told me).  We discussed rpm range and torque output quite a bit when I was ordering the transmission.  This isn't a take-out, it was built to my application, which I think will be a useful thing.

Brian

[bevans6]

Well, Brian has been a busy boy...      I mentioned that I planned to both cut down the front engine mounts and shim the rear ones to get the angle I needed to clear the rear axle.  I cut the front engine mount to lower the front of the engine by about 3/8".  I added .450" shim under the rear engine mount, for a total change of about 3/4" (which has been mentioned as a good starting point in the past).  That should have raised the coupling on the tail of the transmission by a little under 1 1/4".  I took the air governor off the compressor, because it was guaranteed to not fit, and leaving the front of the cradle arms loose I slid the engine back in the bay.  The compressor itself has about 1/8th inch clearance under the roof of the bay, which I call good, and I will remote mount the air governor somewhere on the back of the engine.  I installed the driveshaft and the angle sure looked better at full droop.  I jacked the axle up towards full bump, and the driveshaft still had about 1/8th of clearance when the axle was about 3/8" to 1/2" from the stock, old, decrepit bump stop (new ones on order).  Since my plan is to space the new bump stops down about 3/4", I think I will be good to go on clearances.  The last thing I did was put the fan belt on, and it still fits fine, went on with only a small helping from a screwdriver to flip it over the pulley.

Next is to weld the front engine mounts back up, pull the whole thing out again and start to dress it for final assembly, put loctite everywhere loctite should be, torque all the bolts that should be torqued, put the starter motor back on (I am wrenching on the torque converter bolts through the starter motor hole, much easier to see what I am trying to accomplish).  Put all the plumbing back on, etc.  Then I will have to finally address mounting the oil cooler, which is 26" by 24" by 3" of bloody heavy goodness.  I am at the stage where I can definitely see the light at the end of the tunnel, pretty sure it's not a traim, 80% of the work is done and only 80% left to go...