Expedition engine?

[flatwerx]

Hello SS!
Theres a ton of info and knowledge on the 3116/3126/C7. Thanks for all your experience and input!
I have a friend who has a couple rigs and normally doesn’t sell but is going to sell me one. She’ll be an expedition vehicle but wanna keep her as light as I can (habitat/camper will be no more than 2,500lbs full).
My question is not which engine is better as all 3 engines have their quirks but more on which do you think would make for a better expedition rig engine and why.
I have options:
- 1083 with a 3126
- 1078 with a 3116
- 1078 with a C7

The info I’ve read here and other places has been great. @GeneralDisorder , @Awesomeness , @Suprman and many others have provided some great reading here!
Not looking for anyone to make the decision for me, just some info from the experts. I have been set on the 1083 with 3126 until I was told about the 1078 with the C7.

 

[TomTime]

Well you have to different vehicle chassis, 4x4’s and a 6x6. Maybe choose the chassis you would want and go from there. If you choose the 6x6 then there you go. If you choose the 4x4 then choose the engine.

 

[serpico760]

Hello SS!
Theres a ton of info and knowledge on the 3116/3126/C7. Thanks for all your experience and input!
I have a friend who has a couple rigs and normally doesn’t sell but is going to sell me one. She’ll be an expedition vehicle but wanna keep her as light as I can (habitat/camper will be no more than 2,500lbs full).
My question is not which engine is better as all 3 engines have their quirks but more on which do you think would make for a better expedition rig engine and why.
I have options:
- 1083 with a 3126
- 1078 with a 3116
- 1078 with a C7

The info I’ve read here and other places has been great. @GeneralDisorder , @Awesomeness , @Suprman and many others have provided some great reading here!
Not looking for anyone to make the decision for me, just some info from the experts. I have been set on the 1083 with 3126 until I was told about the 1078 with the C7.

I don't consider myself an expert on the three engines, but I can say if you're going to have a light habitat there's no point in having a 6x6 m1083. Having three axles gives you a 55 mph highway speed limit (in some areas anyway) and you're over the 26k license weight limit, as well as a larger turning radius and more expensive in tires. That's probably why when BAE systems sold the fmtvs as civilian vehicles ( marketed as the SD Brazos) they use the 2 ft longer frame from the m1083 but with only two axles instead of three. If you do go with the 3116 make sure you fix the oil line of death!

 

[GeneralDisorder]

C7. More power to drive the ECO hubs. Better transmission and transmission control. If it's a later model truck it will have the high pinion rear diff also - better ground clearance and fewer driveline problems. Diagnostic capabilities, less wiring from engine to cab, and of course the whole truck will be newer as a consequence of that choice.

 

[ckouba]

...I can say if you're going to have a light habitat there's no point in having a 6x6 m1083...

x2!!

If you don't need the capacity (and at 2,500 pounds, you certainly don't), you would be best to stay with a 2 axle rig for all the reasons already listed. Having ridden in Rick's C7 rig with ECO hubs, I would highly recommend it for all the listed reasons.

 

[fuzzytoaster]

I covered this in a few past posts and believe the A1 trucks between 2003-2004 would be the clear winners in my opinion. They have the 3126 and fall in a narrow serial range where they received many of the newer truck upgrades that became standard on the 2006+ A1R models. Battery disconnect, engine remote start, and etc are nice to have and you've got ABS, exhaust brake, and more HP without physical modifications which are stock on all A1 trucks. These 2003-2004 A1s are still modern platforms which parts and support are available without being price gouged for having a C7 engine. It pays (or saves) to be one step behind the most cutting edge of tech and the slightly older stuff (early 2000's) will be more relevant out of country if you plan to expedition there. You'll have all the perks without any of the down sides. There's also a higher chance of catching an A1 truck that has gone though a rebuild/depot which is always nice.

When it comes to the C7 trucks, I've had 7 A1Rs and still have 3. They're a royal PITA when they want to be and any issues related to the truck, and not a specific component like the engine or transmission, you will be on your own. TM's are electronic and not for distribution legally. The HP flash sounds exciting on paper but the torque output is near the same between a 3126 @ 330 hp vs a C7 @ 370 hp. It's about 40 ft/lb difference and the C7 will be within 3 ft/lb of torque of the limit of the torque converter so unless you're all out in the most extreme conditions you won't see the difference. I do enjoy my C7 trucks but they aren't common enough yet in civilian hands to have any true support beyond major off the shelf components. You will need to be a master of your vehicle.

I have to disagree with the end of GeneralDisorder's last sentence about the A1Rs being newer trucks so everything is newer. The A1R trucks are nearing the end of their useful service life. Not many A1Rs have been rebuilt and remained as soft cabs. Those who are selected go to Oshkosh and become A1P2 and are retained for service. Most A1R trucks will be original but some A1 trucks (2001-2004) and A0 trucks (94-98 ) went through late rebuilds being full resets and are newer in every way. A prime example of this is the 2006 M1078A1R (non-reset) and the 1997 BAE Systems M1078 (2010 rebuilt) trucks I currently have. The A1R shows its age and the M1078 is absolutely mint! I have a M1083A1 w/w that was a late rebuild too.

At the end of the day you will have to evaluate each truck individually and make a judgement call. You can't take the internets word as a definitive so you need to evaluate what skills you have and challenges you're willing to take on should the situation arise. If you want a C7 truck then go for it, they're a blast! But again, evaluate each truck on its own and what you're willing to take on.

 

[flatwerx]

Thanks gents! Just what I was looking for.
@fuzzytoaster I missed your past post on this in my search. Apologies.
@ckouba love your build and appreciate your input/experience.
@GeneralDisorder and @serpico760 always enjoy your knowledge.

I'm evaluating what I need vs what is cool as well. I'm not in a rush which is good but I do hope to get moving soon. Thanks again!

 

[eaw46]

Expedition Portal

The global resource for overland and adventure travel.

expeditionportal.com

Lot of good info here.

 

[Awesomeness]

One thing that I've thought about is the computerization of modern engines. You hear a lot of people say that the older mechanical engines are more reliable (e.g. M35 Duece vs M1078 LMTV), but the statistics clearly show that the newer engines get significantly more reliable as they become more computerized. (There are other non-computerization engineering improvements going on too, of course.)

So why do people perceive it that the mechanical engines are more reliable, when they aren't (not even close)? My guess is that it's the way in which they fail. The mechanical engines may start to fail, but they don't die completely, and you can still drive it until you can fix it. The newer electronic engines have sensors and components that are very reliable, but when they fail, you are just totally stuck (e.g. the engine won't even start without the ECU). As many of our trucks are old, those components have reliably run for 20+ years, and now the plastic/rubber and other delicate portions of them are failing, so do we see a steep increase in failures?

This is pure conjecture, but something to draw your own conclusion on.

 

[Ronmar]

The problem with that chart is it does not say what exactly of the many systems actually failed, just that the truck experienced a failure. These trucks were not designed and built to support a profitable enterprise, so design compromises WERE MADE. All those A0 failures could have been in the electrical system, a system that was significantly changed twice as it morphed into the A1 and A1R… they also changed engines and transmissions in there, so…

cat has made a lot of these engines, sold worldwide with billions of miles behind them. I think the fact that there are still a lot of the 3116 still chugging away speaks well of them in general. The 3116 was the pinnacle of mechanical unit injector technology. Since a lot of them are still in operation, i think it has as much potential for reliable service as anything else. Sadly mechanical diesel is starting to fade, so unless you are prepared to accumulate the knowledge to work it yourself wherever you may be, service when needed(all machines break) may be more problematic. But as mentioned, they also don’t typically just quit, and do not require a computer and a whole different skillset to diagnose and repair…

So what exactly is an ”expedition engine“? Are you planning on taking this thing abroad? As mentioned all the cat engines are perfectly adequate for the task, especially if you are keeping the weight light(my goal as well). Cat parts are available worldwide, but I think I would rather not rely on someone else to provide the supply chain and instead create my own by procuring another engine, controller/governor, turbo and other parts you see fit, and storing them crated and arrange with someone to be able to ship these to you if called upon… Turbo failed, send me crate #4…

If you are staying small and light, I would stick to a 4X$… (no thats not a typo)…

 

[flatwerx]

The problem with that chart is it does not say what exactly of the many systems actually failed, just that the truck experienced a failure. These trucks were not designed and built to support a profitable enterprise, so design compromises WERE MADE. All those A0 failures could have been in the electrical system, a system that was significantly changed twice as it morphed into the A1 and A1R… they also changed engines and transmissions in there, so…

cat has made a lot of these engines, sold worldwide with billions of miles behind them. I think the fact that there are still a lot of the 3116 still chugging away speaks well of them in general. The 3116 was the pinnacle of mechanical unit injector technology. Since a lot of them are still in operation, i think it has as much potential for reliable service as anything else. Sadly mechanical diesel is starting to fade, so unless you are prepared to accumulate the knowledge to work it yourself wherever you may be, service when needed(all machines break) may be more problematic. But as mentioned, they also don’t typically just quit, and do not require a computer and a whole different skillset to diagnose and repair…

So what exactly is an ”expedition engine“? Are you planning on taking this thing abroad? As mentioned all the cat engines are perfectly adequate for the task, especially if you are keeping the weight light(my goal as well). Cat parts are available worldwide, but I think I would rather not rely on someone else to provide the supply chain and instead create my own by procuring another engine, controller/governor, turbo and other parts you see fit, and storing them crated and arrange with someone to be able to ship these to you if called upon… Turbo failed, send me crate #4…

If you are staying small and light, I would stick to a 4X$… (no thats not a typo)…

Thanks @Ronmar !
My plans are for North America, Central, America, South America. I don't have plans to ship the rig. I want to drive it as many places as possible. I'll have another rig with me on these adventures but accumulating spares and storing them is a great idea and not too much of a stretch for me.
Could the itch for overseas travel come up? Sure, just isn't on my radar at them moment. I've spent more time traveling overseas than here, so that's my plan.
Appreciate the insight, knowledge, and questions!

 

[GeneralDisorder]

When it comes to the C7 trucks, I've had 7 A1Rs and still have 3. They're a royal PITA when they want to be and any issues related to the truck, and not a specific component like the engine or transmission, you will be on your own. TM's are electronic and not for distribution legally. The HP flash sounds exciting on paper but the torque output is near the same between a 3126 @ 330 hp vs a C7 @ 370 hp. It's about 40 ft/lb difference and the C7 will be within 3 ft/lb of torque of the limit of the torque converter so unless you're all out in the most extreme conditions you won't see the difference. I do enjoy my C7 trucks but they aren't common enough yet in civilian hands to have any true support beyond major off the shelf components. You will need to be a master of your vehicle.

TM's are available. Just not easily downloaded. I really haven't had any issues with obtaining parts. Things like the 260A alternator (if equipped), high pinion differential, slide out battery tray, etc are really nice features. I have no regrets AT ALL owning a 2008 M1079 A1R. As you pointed out - these will continue to enter civilian hands in the coming years - the military still has thousands of them to auction off.

The 3126b is 275/860, or 330/860. The C7 (when flashed to the M-ATV map) is 370/931. Peak torque is 71 ft/lbs higher. But peak numbers don't tell the whole story - the entire performance curve is different and with the ECO hubs it's a totally different truck than any other FMTV. People are very surprised by my truck. It's like a sports car compared to stock.

One specific area of note between the 3126 and the C7 is in the ECM itself. C7 ECM's are VERY common on ebay, etc and it's no problem to pick one up for $100 to $500 any day of the week and reprogram it. They don't have the capacitor/battery issue of the early 3126 ECM, in general I have found them more reliable and 3126 ECM's are actually kind of hard to find. Either way you go I would recommend programming and testing a spare and carrying it onboard. I carry spares on board my truck for virtually every electronic component.

I offer programming services for both 3126 and C7 ECM's as well as CTIS controllers (the black one's anyway - haven't messed with any programming of the green ones). I can clone an existing ECM to a used unit in order to carry as a spare, etc.

I have to disagree with the end of GeneralDisorder's last sentence about the A1Rs being newer trucks so everything is newer. The A1R trucks are nearing the end of their useful service life. Not many A1Rs have been rebuilt and remained as soft cabs. Those who are selected go to Oshkosh and become A1P2 and are retained for service. Most A1R trucks will be original but some A1 trucks (2001-2004) and A0 trucks (94-98 ) went through late rebuilds being full resets and are newer in every way. A prime example of this is the 2006 M1078A1R (non-reset) and the 1997 BAE Systems M1078 (2010 rebuilt) trucks I currently have. The A1R shows its age and the M1078 is absolutely mint! I have a M1083A1 w/w that was a late rebuild too.

For sure each truck will have to be judged on it's specific merits. Regardless of reset or no reset the A1R trucks will retain a higher resale being the last trucks made available to the civilian market in complete form and seem to still be appreciating in value. Depending on the deal he is getting from his friend and the condition of the respective trucks will definitely determine the right course.

To the OP - post pictures/videos of each truck so we may see how they are optioned and their condition. There may be a clear right answer with more information.

 

[87cr250r]

Food for thought, control modules with batteries are typically designed for a 25 year life expectancy. That can get much shorter at higher temperatures. I have successfully replaced batteries in one specific control module.

 

[GeneralDisorder]

Food for thought, control modules with batteries are typically designed for a 25 year life expectancy. That can get much shorter at higher temperatures. I have successfully replaced batteries in one specific control module.

The early 3126 ECM had problems with an on board power source that, once depleted, would render the ECM inoperable. Most of these ECM's are off the road having already been swapped out. The later ECM's and the C7 ECM have a power source for date/time settings so they can time stamp event log entries, etc. I have yet to find a military ECM with an actual working battery. They are all dead from what I have seen - fortunately CAT changed up the software so a dead ECM memory power source doesn't affect their operation. They just revert back to their manufacture date/time every time they are power cycled. In practice it has been a non-issue.

As far as replacing them - could be possible. I haven't tried. I've swapped out many batteries on PC motherboards - both CR2032 style as well as the older style one's soldered to the boards. If anything, since the ECM doesn't need the battery to function, I would be inclined to just delete it so it can't leak and damage the board.

 

[Third From Texas]

Just my two cents:

As mentioned above, do you want the 4x4 or the 6x6 chassis?

That's the bottom line here, IMO.

The M1078 A1R w/C7 "should" have the upgraded rear dif that lets the drive shaft connect pretty much straight back. So will the 6x6 (any model). But the M1078 A0 with the 3116 has the drive shaft of doom that juts down at a crazy steep angle of attack (which is a whole other thread on vibrations, etc). I'd avoid it anytime there is an option to do so. ymmv

So I'd take whichever of the two remaining trucks that has the frame length that best fits your needs.

Mine is my daily driver and it's just me and the dawg. The 4x4 is a lot easier to whip around a Home Depot parking lot and fit in a single space. And the resale value on the A1R base truck is going to be waaaay more than an A0 or A1. A 12.5 to 14 foot hab is easily doable on the 4x4, but not much longer.

But if it's going to be a three person habitat and a lot more serious off-roading, I'd lean towards the bigger rig. You can toss a monster sized box on the 6x6. Of course, the maint and tires are 150% that of the 4x4.

Pros/cons with either variant...

But given your choices, I'd scratch the M1078 A0 all else being equal.

 

[87cr250r]

A straight driveshaft is not necessarily a good thing. In fixed applications it's standard to build 7-15 degrees of offset into cardan shafts because you need oscillating motion to keep them lubricated. My experience is transmission between to fixed locations.

 

[flatwerx]

Just my two cents:

As mentioned above, do you want the 4x4 or the 6x6 chassis?

That's the bottom line here, IMO.

The M1078 A1R w/C7 "should" have the upgraded rear dif that lets the drive shaft connect pretty much straight back. So will the 6x6 (any model). But the M1078 A0 with the 3116 has the drive shaft of doom that juts down at a crazy steep angle of attack (which is a whole other thread on vibrations, etc). I'd avoid it anytime there is an option to do so. ymmv

So I'd take whichever of the two remaining trucks that has the frame length that best fits your needs.

Mine is my daily driver and it's just me and the dawg. The 4x4 is a lot easier to whip around a Home Depot parking lot and fit in a single space. And the resale value on the A1R base truck is going to be waaaay more than an A0 or A1. A 12.5 to 14 foot hab is easily doable on the 4x4, but not much longer.

But if it's going to be a three person habitat and a lot more serious off-roading, I'd lean towards the bigger rig. You can toss a monster sized box on the 6x6. Of course, the maint and tires are 150% that of the 4x4.

Pros/cons with either variant...

But given your choices, I'd scratch the M1078 A0 all else being equal.

Thanks for the input!
It's just me and sometimes my girlfriend (she doesn't like to get out as much as I do). The habitat will be comfortable for 2 but more than likely it'll be just me.
I don't need a shower inside (outside would be nice), just the toilet part of a bathroom so that can be stored away.
I've seen some nice S-280 builds as well as some pop up campers (Alaskan). I believe @tennmogger has one on his Unimog. Apologies if I'm mixing up member's names.
The 6x6 with the 3126 was my first choice but honestly, I think it was more of a cool factor. The 1078A1 does have the high pinion rear. Keeping weight and costs down is ideal so I'll probably go that route.
I'll be heading out to my friends in a couple weeks and that will be the first time driving a 6x6 for me. Drove a couple 4x4's in Bahrain.
Ideally, I'd like to keep the bed, be able to unload the camper/habitat and use the rig as a truck when needed but I do a lot of off-roading/camping now and want to do more for longer times out. So I may end up with 2 if it comes to that
@GeneralDisorder I'll try to get some good video when I get out there.

As always gents, thank you for your time and knowledge.

 

[GeneralDisorder]

A straight driveshaft is not necessarily a good thing. In fixed applications it's standard to build 7-15 degrees of offset into cardan shafts because you need oscillating motion to keep them lubricated. My experience is transmission between to fixed locations.

First off they aren't straight. Nor is this a fixed driven object. Not to mention they changed this to the design already used by the 6x6 precisely because it was problematic and the 6x6 was not. Since the change they have been running the same design for 20 years and the incidence of u-joint and driveshaft problems and associated vibration problems has decreased significantly.

 

[Ronmar]

Yep, the trucks with low pinions are running the shafts way outside the angle/rpm charts which cause longitudial vibrations. The rear shaft is right at the 61" max length for this type, so has more mass which is what gets moved to cause the longitudinal vibrations in steep angles@high RPM driveshafts.

Now the front shaft is equally as steep, but it is shorter/has less mass.

Reducing shaft angle or RPM are good things for this vehicle...

 

[Third From Texas]

Thanks for the input!
It's just me and sometimes my girlfriend (she doesn't like to get out as much as I do). The habitat will be comfortable for 2 but more than likely it'll be just me.
I don't need a shower inside (outside would be nice), just the toilet part of a bathroom so that can be stored away.
I've seen some nice S-280 builds as well as some pop up campers (Alaskan). I believe @tennmogger has one on his Unimog. Apologies if I'm mixing up member's names.
The 6x6 with the 3126 was my first choice but honestly, I think it was more of a cool factor. The 1078A1 does have the high pinion rear. Keeping weight and costs down is ideal so I'll probably go that route.
I'll be heading out to my friends in a couple weeks and that will be the first time driving a 6x6 for me. Drove a couple 4x4's in Bahrain.
Ideally, I'd like to keep the bed, be able to unload the camper/habitat and use the rig as a truck when needed but I do a lot of off-roading/camping now and want to do more for longer times out. So I may end up with 2 if it comes to that
@GeneralDisorder I'll try to get some good video when I get out there.

As always gents, thank you for your time and knowledge.

You should check out Neil's build. One of my favorites...

He too retained the bed so the truck is still multi-role. Used a S280 and set it up so he can drive it on/off.