Different Diesel Direction

[M715mike]

Oh wise and all-knowing M715 gurus! I humbly kneel before you and to ask for opinion, guidance and support for my diesel conversion project.

Hello everyone: my name is Mike Bennett, I live in central CA and I'm addicted to the super cool rugged go-anywhere looks of the M715. First time poster: what a great site! I have a '69 M715 I've recently purchased from my brother. He had obtained it from one of the National Guard units and thought it was pretty straight and complete. He promptly took everything off down to the chassis intending to do a full rebuild and then lost interest. Years went by and I finally had the opportunity to purchase it from him. It seems complete to my untrained eye with the exception of the engine: no engine.

I have a genuine desire to make this truck diesel for a variety of reasons. I understand there are multiple ways of doing this.

Within the next 2 months, I will have the opportunity to purchase a '91 Dodge Cummins 1 ton 4wd truck at a very reasonable cost. First generation Cummins, with intercooler and manual pump, NV4500 tranny. Old style body, sheet metal tired, doors loose, beat up but usable service body on back. Big winch on front. Runs and drives great, truck has only 70,000 miles on it.

I am leaning towards putting the M715 body on the '91 Dodge 4wd Cummins chassis. Seems to me that may be the best of both worlds: the look of the M715 on a modern chassis. I understand from the archives and all the excellent info on this site about the lack of space in the M715 engine compartment for a 6bt. Because the wheelbase of a M715 is 126 inches and the wheelbase of the '91 Dodge is 131 inches, I have to "stretch" the M715 body 5 inches to match the Dodge anyway. I realize simply increasing the space between the bed and cab would be easiest, but if I stretch the engine compartment instead, it should theoretically be possible to fit the 6bt.

And so here is my question to all you experts out there. Theory aside for the moment, please give me your practical opinions. What do you think of stretching the M715 engine compartment sheet metal: hood, outer and inner fenders, enough to allow a 6bt to fit with stock fan, and room for a radiator and intercooler? Would you stretch the hood and fenders, or add length at the fire wall, effectively pushing the hood hinge point and fender mounting locations out, say 6 inches? This would allow the continued use of stock fenders and hood, but may be much more difficult to accomplish than simply stretching the hood and fenders themselves. I don't know a lot about sheet metal work, though it seems like this sort of thing is done routinely in the hot rod world. I am experienced in engine swaps and custom vehicle fabbing issues having completed a sbchevy fuel injected computer controlled engine swap into my '75 Land cruiser 12 years and 80,000 trouble free miles ago. I think I understand the bigger issues associated with this proposed chassis swap, but I'd love to hear other opinions, especially about lengthening the hood and fenders.

Thanks for the help,

Mike Bennett
Madera, CA

[gimpyrobb]

Well to give a quick answer, don't "stretch" nothing. I have heard that there is alot of room between the firewall and the dashboard. Make a custom motor hump, or graft in something from a van so you have a removable pannel. I have pulled no tape measures, I am just going from what I retained from this site in other topics. Someone else will chime in with a better answer/reason soon.

[Doug]

I'd look real hard at moving a portion of the firewall back before I'd consider stretching the exterior sheet metal. Same with moving the drivetrain to your existing frame, or at least shortening the dodge frame to meet the M715's wheelbase.

I'm not saying it's impossible, but it sure would be a heck of a project when there are easier ways to skin the same cat.

[Barrman]

Welcome!

The biggest "don't do it" reason I can think of is the under bed tool box. You will have to cut it up to make the bed sit anywhere close to level on the Dodge frame.

Other than that, take lots of pictures, buy stock in a welding supply company before you start the project, build it like you want it, not how somebody tells you to and enjoy.

[M715mike]

Thanks for all info, I do appreciate the thoughts.

I agree pushing the center section of the firewall back into the cab would be easier, but I'm unsure how far back I'll need to go at this time: my wild guess would be in the 8 inch range because of my need to run the stock fan and include an intercooler. Pushing the firewall back is easy, figuring out how to comfortably reach the shifter which has also moved back 8 inches inside the cab may be more difficult. This option would be much easier with an auto tranny. Another drawback to this option IMHO is the increased access issues with the back half of the engine.

I understand the relative benefits of doing an engine swap into an existing vehicle chassis with possible upgrades like axles and transmission. My initial concern with the 6bt was one of strength of the existing 715 frame. I assumed the front section of the M715 frame was designed with the 230 Tornado engine in mind. Putting the 6bt into that frame (sheet metal issues aside for the moment) makes me wonder how well the original frame would hold up under such a severe increase in hp, torque, and weight.

Thanks for observation regarding the under bed tool box. I'd hate to lose it as it is one of the many unique features of the M715 that sets it apart from everything else.

Thanks again,
Mike Bennett

[Doug]

6bt- They've been installed with just a body lift sans intercooler.

Just tossing thoughts out- recess the rad and intercooler into the valence as much as possible, electric pusher fan or fans installed on the front of it. Then the body lift, or 2-3" into the firewall, or combination of both. 8 inches seems like a lot.

Oh, the frame. It was designed for the 230, but was also designed as a 1-1/4 ton truck. It is lacking in a couple areas. Rear half is not boxed, that could be done. Rear spring hangers are single shear as opposed to double shear. These are a problem and can break, but it would be an easy enough fix to make them double shear. That said, many of the guys hear can tell you their own story of overloading them. Don't recall hearing of anyone damaging a frame.

[Mikel]

I recently parted out a 1990 Dodge Ram W350 4x4 with the Cummins, I was shocked at how flimsy the frame was. It didn't look much beefier than my J300's, and in some areas, I think my Jeep frame was stronger (the front half is fully boxed).

I vote for keeping the M715 frame.

[2ndA]

Moving bodies around on frames and getting them level is easy: Body lift. Hack your spacers as needed and voila, level bed/cab. Also, raising the cab an extra couple inches more than the bed should help clearance issues with the engine and reduce the amount of movement needed on the hump. Lastly, that shifter point can be about anywhere, just means you'll have to get creative in bending the shifter itself.

Oh, shorten the frame, pleeeeez.

[LuckyPabst]

I'd be keen on shortening the Dodge frame to fit the 715 WB. My second suggestion would be to lengthen the cab to make up the difference and hack the firewall as needed to fit the engine. You could add the length to the doors or to the area behind the doors or split the difference between the two - you'd gain leg room for sure.

Chris

[gun512]

Here are some pictures of how avalanche engineerging put a 24v 6bt with a NV5600 in a M715.

http://www.avalancheengineering.com/m715.htm