6BT Help for the 715

[Joel]

I have been gathering parts for a while now and haven't been around long enough to do much. I am finally getting the time and going to start the build.

I have 2 questions before I get knee deep in this build.

I have a 90 Dodge 6bt w/ 727 trans. I also have a 95 F800 ford w/ 6bt and a Fuller 6spd trans. I bought the F800 for the trans and the 6bt has a bad cylinder and burns oil. I am not looking for much over stock power now but I know that I will get bit by the horsepower bug and want more in the future. I was quoted that 2000$ would fix the 95 6bt. I am wondering if it would be a good idea to swap the 95 6bt parts (head, pump whatever else) onto the 90 block or just fix the 95 6bt and use it. I hope some of the Cummins guys can let me know which way is the best way to go. I am sure it isn't as easy as swapping parts even though I heard that the Cummins engines have the same block and a lot of other similarities.

Next piece of advice or opinion I am looking for is; do I swap the M715 body on the F800 frame with rockwells and build myself a 25,000 lbs GVWR truck or stay with 1 ton axles under the M715 frame and get a diesel powered 1 ton? I am looking for a work truck/ expedition type vehicle that can go most anywhere. I know I won't necessarily need the 25,000 GVMR but it would definitely be solid. There would be a lot less fabrication with swapping bodies.

[Arch8]

For your intended use there would be lots of reasons to just do a body swap. If you were to modify the M715... Sure, you have the engine and transmission but then you'd want to change the transfer case. And likely to follow would be axles with disk brakes. You see where I'm going with this? A complete overhaul. If you're happy with the F800's gear then most of the work has been done for you. And like you said, it would be a solid, go anywhere truck. Oh, and parts would be easier to get a hold of too.

[tndonor]

As far as swapping parts from the 90 ot the 95 there are several things to consider. The 90 was a non intercooled motor, the 95 was intercooled. The spray pattern into the fuel bowl will not be correct. To finish the swap, you would have to lock the timing on the 95 IP, take the timing cover, pump gear, and injector lines.

It is usually cheaper to sell a complete 1st generation motor and buy a motor of you choice.

With the fuel potentially not going into the bowl, you will probably get hazing, lagging performance, and high egts.


my .02

[tndonor]

Oh yeah, lift pumps are different as well.

[Joel]

The 95 6bt is complete (though w/ a bad cylinder). What I am hoping to do is use the 90 block (and as many internal parts as possible) and put everything else from the 95 onto the 90 block. That way I only have to buy new piston(s) or rings and not get have to get any work done to the block.

I don't know if the bad cylinder is rings or the cylinder wall yet. I am going to pull the head and take a look in the next few days. Can I get a sleeve or would I have to get the cylinder(s) bored over to fix the 95 block if it is the cylinder?

[tndonor]

You can sleeve the cylinder or bore it. If you sleeve it, it takes special tools to get it in and you will have to sleeve all the cylinders to match. Or you can bore the walls and just get oversize piston (that is what I would do). You can overbore 60 over if I recall correctly.

[Joel]

Thanks, I just got a hold of a service manual and it says I can bore over twice if it doesn't exceed the limit. That is the route I will have to take.

Since this is a medium duty Cummins and mounted front and rear I am thinking about just swapping the M715 body onto the F800 frame with Rockwells instead of swapping motor & trans between the 715 frame. I will end up with a stronger frame and less fabrication and headache.