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Psychlopath's Cummins swap

55K views 170 replies 41 participants last post by  psychlopath 
#1 · (Edited)
Well, I figured since I’m starting to make some headway, maybe I should begin a write up. I’ve seen several that deal with ongoing builds, so I wont feel so out of place here.

The idea of putting a Cummins into my vehicle has been kinda-sorta kicked around for a while. I finally got to a place where I have the time and know-how available to me. I also wanted to try to do something that, in retrospect wound up being a LOT larger than I’d planned, but could also be done by just about anyone. So the idea is to try to keep “custom,” at bay, frame hacking and special know how stuff to an absolute minimum.

I got ‘hold of a 91 6BT out of a wrecked bus. Several of the engine doodads were broken on it, including what used to be an engine mount (This bus used the front engine mounts, which I will be NOT using) and an alternator mount. One thing that was a surprise, was it has an air to water aftercooler on it. From the pictures, before I bought it, it looked like it had no charge air cooler. Score one for me! The plan was to add a cooler from a Dodge after the vehicle was running to reduce the initial headache.

After receiving the engine, all I could really do ‘till the old engine came out (A healthy 400 with some mild warming) was try to make it look half way decent and deal with any issues I could see right now. Having a friend who was a heavy equipment mechanic for many years was helpful in giving it the once over.



The obvious problems I found were that the front timing case locating dowel pin was starting to back out (AKA: Killer Dowel Pin or KDP, if youre into that sort of stuff) and it looked as if the oil sump had sat for years in the dirt; It had some pin holes.

To fix the dowel pin, I hammered it back into its proper spot and made a crappy little retainer out of some thin sheet that I found somewhere. It’s home for good, now.





As for the sump, I’m having to get a friend to weld up the pin holes before I get it painted and attached.

When I got the engine, it had this crazy contraption of steam pipes and electrical tape involved with the heater hoses. Part of it was some sort of cobbled together throttle linkage that looked like it’d been backed over by a Buick and the rest must have been how they figured out they could shut heat off to the passenger compartment in the summer.



Here’re some pictures of the engine paint job. I was inspired by a few pictures of marine engines I’d seen floating around through some magazines. I wanted to go a step further and have everything really looking ship-shape; bolts, mounts and the whole shebang, but not only is it a pain in the ass, but bolts don’t hold paint well as far as I can tell, and I tend to get a little carried away with one project and leave the little things behind.





My engine came sans motor mounts, so that left me a lot of room to build my own or figure out what, exactly, would work best for this particular application. After a quick test fit with an engine hoist (And DAMN, will it be close to that radiator! SO close, I don’t think I’ll be able to use any of my V-belt pulleys…) and some online detective work, I settled on the vanilla Dodge 24V engine mounts. They are stout as hell, and seem to lend themselves to the stock engine towers in the Bronco pretty well. Plus, it fits in with the theme of fabricating as little as possible.





I DID have the minor issue of having the turbo drainline (My turbo came set up BACKWARDS of all the ones I've ever seen! May make routing exhaust easier, however...) attempt to get friendly with the right hand motor mount. Nothing a little cutting of that drain tube and running of flexible line cant fix.



As far as getting the engine to work with the transmission, I wanted to stick with the C-6. I knew it would be a challenge; I still haven’t gotten EVERYTHING worked out with it, but it would do a few things for me. One, since it was a fresh rebuild, with a few extra goodies tossed in, it should hold up well to the mild amount of power I intend to get from the Cummins. Two, being a C-6, they are everywhere and are pretty easy to re-build, when the time comes. And three, it doesn’t have any of the PITA that hooking an E4OD (Probably a much more ideal choice, honestly) would have brought into the equation…like getting another transfer case or desperately hoping I could get the front drive shaft to clear if I kept my NP205.

I did a ton of reading on which engine to transmission adapter to use. I wound up going with the one from Diesel Conversion Specialists. Their customer support has been great so far, and the price was better for the package I thought I’d wind up needing than the other two companies I found out there. When the parts got here, they seemed to be of pretty good quality. The flex plate adapter wasn’t QUITE what I would have let leave my shop if I were turning this stuff out, but it’ll be functional.



Speaking of “Flex plate,” the one I had let me down. I hadn’t even considered that since it was out of a heavy vehicle there may be some difference between what I have and what I need. The one I had wound up being too large. I ordered one online, with the proper diameter and now I’m good to go.

Since I decided that this engine swap was going to give me a chance to do some of the other things I’ve always wanted to do, but never had the motivation, one of the other things I’m adding is air conditioning. I haven’t fully worked out the system yet, but the PLAN is to use the stock Bronco under dash stuff and go with whatever else fits under the hood. I’ll get the biggest condenser I can and run the compressor that fits on the engine. There was NO compressor bracket on the engine when I got it. So, back to the Internet for some forum searching. I found that I can use a Cummins bracket that went in Freightliners and Ford medium trucks to mount the compressor higher than the stock (yet cheap) Dodge mount. With Dodge’s idea, I’d have to cut out more of the front cross member than I want (which is none…we’ll see how that goes) AND a section of the frame. So, I went on a 4 week long trek trying to find a salvage yard, dealer or supplier near me who would deal with a single guy and not just a fleet shop. “Diesel Power,” not too far from me fit the bill. RL there helped me out a great deal with his willingness to check part numbers and actually order the damn thing for me.

So, now I have this:



The same day I picked up my compressor mount, I went to get a nice new compressor for a Dodge with a Cummins. When I bolted it on, I noticed (you cant really tell in the pic) that the AC pulley sits a little off from the water pump; Maybe about two grooves.



More reading and I found out that only a compressor from a medium truck will properly line up. So that’s on order now.

While the engine is out of the vehicle, I have a few things to get working on to make things a little nicer once it gets into its new home. First, I plan to paint the firewall and underhood white. I think it looks clean and it helps ID leaks. I’ve been too lazy to really mask the thing off, yet, though. Maybe tonight…

I also now have a transmission bellhousing to figure out. It was broken when the old engine was removed. I wish I could claim responsibility, cause I’d be a lot less mad but…It was the other guy.



Next few hurdles I see being a huge problem are getting the vacuum signal modulated from the vacuum pump (I picked up a vacuum pump/power steering pump from a Dodge) to the transmission. There’s a workaround mentioned in a pretty damn good write up on this very site, but our throttles are going to be set up differently, so I think I’m going to have to modify the idea some.

And that's about where I am right now. Transmission should be physically out tomorrow and I'll figure out if it can be welded or if it needs to be replaced. Hopefully that will be the last backwards step...

Feel free to send any ideas on things my way. Comments are welcome.

More to follow.
 
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#2 ·
Looking good

I'm anxious to see your progress on this project...I hope to gain some insight for my project. I recently purchased a bread truck, so planning a 4bta conversion for my 79 (also going to keep the C6). What do you plan to do for gearing in differentials, and or tire size to get cummins in sweet spot for rpm's. I did the E4OD 1st & 2nd gears in my C6, so I'm hoping that I may be able to go to 3.00:1 diff gears and not have it suck too much for accelerating. btw..As for your engine paint job...wow..thats bold...I havent seen those two colors used together since leisure suits of 1970's :histerica
 
#3 ·
The gears are 4.11 for now and the tires are 35" and wont be changed. They're the last item to deal with, but I dont see it being a huge deal. I intend to get it moving under it's own power before I make the final move.

I think the biggest issue with this build is going to be that I'm in Texas and I dont like mud.

You'll be ahead of where I started since you have a whole donor vehicle and that's a good thing.
 
#9 ·
Get that shiitake started. I'll race ya.

This weekend, I get to finish part of my alternator bracket and weld up the weak spots on the oil sump.

I got hit pretty hard by a cold, so things stood VERY still this week. And...well, may stagnate this weekend too, cause DAMN the thought of lifting my dead ass off the couch hurts.
 
#10 ·
Today's entry:

Not too much done. FINALLY got the oil sump to where it holds water and, therefore, oil.

Welded up the new lower alternator mount. Or...HAD it welded, since I tend to do more harm than good with a welder.

The lower weld is super fat because it's covering one of my botched attempts. It's good to have people around who know what they are doing, even if they couldnt give two squirts of piss about a Cummins swap.



Next step should be some transfer case work (likely with a twin-stick write up...schweet!!), to include new gaskets and seals and now, waiting for a new transmission mount.
 
#11 ·
Nothing exciting to add. Got the transmission to the guy who's doing the work on it. Got the twin stick mods done. Pushed the thing out of the work area and cleaned up everything so it's a somewhat respectable work area. Organized. Ordered a starter.

Near future projects: Getting the fuel tank drained and hooking up a return line, chopping on the block to fit the starter, painting the engine bay and installing the transmission and transfer case.

Mid term schedule: Fit the engine, move the transmission back 4 inches (not 100% sure if I'll need this yet) install the AC underdash stuff, wire the engine bay.

The plan was to have all the short term done next week, but the starter isnt here yet, the new transmission mount isnt delivered yet, the tranny work is going to take longer than I thought and work is picking up as of the 1ST of November.

So, now it's a waiting game. Again.
 
#14 ·
You do with the one I got, at least.

You have to chop on the transmission with all of the adapters I'm aware of.

As for the block, it's a small amount near the rear passenger side, but I'm not sure yet. Once I get the starter, I'll post up pictures. Hopefully THAT, at least, will be here today.
 
#15 ·
Hey psych, do you have a part number for the air-con compressor bracket? I seem to have forgotten about this need, as I have a 94 dodge truck engine with a/c mounted low as well. I may be able to locate one before I get home so as to save some time. I will be another career builder with my swap as I dont have much time off in my rotation. Anyway I am subscribed here, keep her moving forward!
 
#16 ·
Yep! It's Cummins P# 3930888 and your Dodge compressor will fit on it. If your engine is out of a Dodge (and you said it was) it looks like you'll NEED the Dodge compressor.

My engine came out of a bus and it seems like the serpentine system is set a little farther out from the block than the Dodge setup. I had bought a new Dodge compressor and the pulley sat maybe 1/8" too far towards the block to line up with the water pump.

I'll be ordering a Freightliner compressor soon and that's rumored to solve the problem.

I wish I had more to update, but for now, I'm still waiting for transmission work to get completed and am working on projects that arent engine related like mounting AC stuff under the dash and all that good stuff.

I ordered the vacuum control module, which I forgot about 'till today.

So, still just...waiting.
 
#19 ·
Awesome build - I want to see this thing run!
 
#21 ·
I'm not positive, but I suspect a C6 off an early 6.9 diesel will fit on the destroked adapter without any clearancing of the bellhousing at all.
 
#24 ·
I'm not positive what they did on mine, but Dynamic Racing in CT built it for $1700, which I thought was very reasonable. They could have built the max competition version for $3000, but I couldn't afford it. I don't think there is much if any difference in the valve body, as the trans shifts based on vacuum signal, (via the VRV mounted on the throttle) what IS important is the stall speed of the converter, as the Cummins will hit peak torque at around 1700-1900 rpm, where a gas engine is barely above an idle at that rpm. My converter is a billet unit, with 1200 rpm stall speed. Don't underestimate the importance of the converter, it's critical, both for longevity and performance.
 
#30 ·
Not much in the way of updating. I did lots of not working on the Bronco this weekend and not much in the way of working on it. But I wanted to do SOMETHING.

A small thing that needed to be done was to get a way for a fuel return line to the tank. I wanted something kinda trick rather than just drilling a hole if I could manage and I think I figured it out.

I wanted to replace this little check valve left over from the evaporative system:



It plugs into a grommet on the top of a fuel tank and had a rubber hose on it that used to go to a little charcoal canister. I dont think I need this with a diesel, so I wanted to gut the check-valviness out of it and just run the return line through the stock hard lines and dump into the tank. But, as it turns out there's a metered orifice in the valve and drilling it out would not leave much strength there. On top of that, the inlet nipple is smaller than the fuel return line on the engine.

So I wanted to make another one. I found a piece of phenolic something or other and chucked it up on the lathe. After a few measurements and cuts, I had this waiting for a plunge cut:



Not too shabby for having no clue what I'm doing, eh?

Drill a quick hole to make sure it's centered and give me a guide hole:



After the cut, this thing is looking pretty much like it may work! Dayum, it's tough being this good:



They measure up pretty well.



A little tappage:



And my AN adapter fits in just fine:



Now I can run whatever size fuel return line I need right to a -6 adapter.

Not a terrible amount of work, I know...but it is what it is. At least I can get the tank back in tomorrow and not have to worry about that part any more.
 
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