The '68 Cummins 4bt Brick Build

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I got back in the garage last night and fabbed up a front crossmember. I still need to cut out the factory one and add another in its place, just under the frame rails. Then, lock in the passenger motor mount.

 

[big a]

I'm sorry it's been awhile since I last posted. Neither the thread nor the project is dead!!!

Life has been super busy beyond just the Texas heat (which this yr hasn't been near as bad as past yrs). I had to paint and rearrange 3 bedrooms and do a total house cleaning in preparation for the arrival of our 3rd child!!!! All the kids got new rooms and no one feels left out, except my Bronco, lol!!! Well, our new daughter was born a cpl wks ago. I took a wk off from work and was intermittently able to get back to the bronco.

Also, I got a little side tracked as I have a friend I talked into doing a diesel swap pulled me away for a bit. He has an air conditioned shop He's putting a Mitsubishi 4D55/4D56 diesel in a Bronco II. Been fun, but time to get back on track!

I cut out the passenger mounts to reposition the engine. You know the ol tack first and finish weld later. Well, I should've followed that and things would've been easier because I kept changing my mind. Anyway, the Bronco is holding the engine under it's own weight!!! The engine is square to the frame and I'm finally happy with it's position! I'm waiting for a clocking ring to come in tmrw to position the xfer case so I can lock in the tranny mount. I'll post some pics later this wknd or Monday to get this thread rolling again!!!

Btw, since it will be cooling off soon and life has normalized, the project is back on!!!!!!!

 

[stupidboy]

what vehicles do you find a 4bt in?

 

[Dbteak]

Yea, the build is back on. I thought you gave up. Congratulations on the new rug rat and future bronco driver.

 

[big a]

what vehicles do you find a 4bt in?

You find them in step vans like Frito Lay trucks and Hostess trucks. There are quite a few on eBay. When Hostess went out of business recently, they auctioned off tons of these vans. Folks buy them up and part them out. Pretty easy to find, but not cheap! Especially when doing a swap!

You can find a great wealth of information on 4btswaps.com, but I'll warn you, read read read before you post. Those are not the friendliest folks in the world on that forum. If you read through some posts, you'll see exactly what I mean. I don't know a ton, but ask any questions you want and I'll help how I can!

 

[big a]

Yea, the build is back on. I thought you gave up. Congratulations on the new rug rat and future bronco driver.

Hey Doug! How's it goin??? You rackin up the miles on your truck?? Every now and then I go read your thread and get motivated all over again!!!

Never!!!!!!!!!!! I always go into hibernation mode during the dog days of summer. Just too freakin hot to be motivated!

Thx!!! She's a gem!!! I can't believe she's only 2 wks old and already has the diesel bronco bug Must be contagious!!!

Well, I followed your footsteps slightly and went out and bought a CPL 1839. It is a brand new Reviva rebuild. Zero miles! I stripped down my CPL 858 and was astonished by the shape of the block. The bearings looked almost new! I'm just gonna do a light rebuild on it, ie hone, rering, lap the valves, reseal and resell it! I should be able to make some good cash on the deal to add to the Bronco fund! I'll post more about this later with pics!

 

[Dbteak]

Hey Doug! How's it goin??? You rackin up the miles on your truck?? Every now and then I go read your thread and get motivated all over again!!!

Never!!!!!!!!!!! I always go into hibernation mode during the dog days of summer. Just too freakin hot to be motivated!

Thx!!! She's a gem!!! I can't believe she's only 2 wks old and already has the diesel bronco bug Must be contagious!!!

Well, I followed your footsteps slightly and went out and bought a CPL 1839. It is a brand new Reviva rebuild. Zero miles! I stripped down my CPL 858 and was astonished by the shape of the block. The bearings looked almost new! I'm just gonna do a light rebuild on it, ie hone, rering, lap the valves, reseal and resell it! I should be able to make some good cash on the deal to add to the Bronco fund! I'll post more about this later with pics!

I have put about 3500 miles on it. I am averaging 23-24 mpg and it doesn't really care how I drive it. I still want to try a 3.00 or a 3.25 rear gearing to see if I can get better mileage without hurting performance. The 3.50's that I have in it right now seem like the best combination. I can shift 1-3-5 when I am lazy and pulls hard in any gear.

The only issues I have had are a leaking brake distribution switch and a leaking aux tank filler hose. I am also going to go back to the stock clutch cooling fan instead of the electric fan. On the freeway at 95 deg. the fan is always on and just putting around town the fan is off. I want the reliability of the clutch fan.

 

[big a]

Yeah, I've been kicking around gear ratios also. Here's some info you may have.

 

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So, lowest fuel consumption is at peak torque which is at 1700 rpm. Also, at this point this engine is still building hp to 2300 rpm. I'm running an NV4500 and plan on running 285/70R17. I created a spreadsheet and compared 3.25 to 3.50 gears. 3.25 will put me at peak torque and best fuel mileage at 70mph in 5th gear. The tranny has such a low first gear that I can run as tall a gear as I want. I only want to tear into my axles once, so I'll prolly go with 3.25. Just need to source them.

 

[big a]

I have put about 3500 miles on it. I am averaging 23-24 mpg and it doesn't really care how I drive it. I still want to try a 3.00 or a 3.25 rear gearing to see if I can get better mileage without hurting performance. The 3.50's that I have in it right now seem like the best combination. I can shift 1-3-5 when I am lazy and pulls hard in any gear.

The only issues I have had are a leaking brake distribution switch and a leaking aux tank filler hose. I am also going to go back to the stock clutch cooling fan instead of the electric fan. On the freeway at 95 deg. the fan is always on and just putting around town the fan is off. I want the reliability of the clutch fan.

That's awesome!!! 3500 miles!!! I can't wait!!!! We are going straight to the mountains in New Mexico on a family expedition once I'm done and have the bugs worked out!!!

Well, I've also been kicking around the idea of running a fan clutch versus an electric. It'll just be one less thing to fail. I'll have to source one though as my engine didn't even come with the fan hub. The great thing about this motor is the fact that it's all mechanical!!!! No costly electric computer to fail! I'm curious if you go back manual how much it will affect your fuel mileage... I'm still undecided...

 

[Pa PITT]

.. Glad to hear your build is going the way you want.
I too thinks mine runs hotter on the Hy-way than it does say just in the pasture. But I'm 99% of the time in the pasture at say 5 mph. I do run an elec. fan on a toggle. If I catch my temp up to say 185 . I flip the switch and it cools down to about 100.

 

[Dbteak]

So, lowest fuel consumption is at peak torque which is at 1700 rpm. Also, at this point this engine is still building hp to 2300 rpm. I'm running an NV4500 and plan on running 285/70R17. I created a spreadsheet and compared 3.25 to 3.50 gears. 3.25 will put me at peak torque and best fuel mileage at 70mph in 5th gear. The tranny has such a low first gear that I can run as tall a gear as I want. I only want to tear into my axles once, so I'll prolly go with 3.25. Just need to source them.

If it was mine I would go with the 3.5 first. That seems like a better RPM at cruise speed. With 3.25 you are barely into the turbo at 65mph plus 3.25 gears are very pricey. That is why I am going to try the 3.00 gears first to see if my mileage goes up.

Mine is running 2050 at 65mph and it is very happy but I think it is hurting fuel economy.

 

[Dbteak]

Yeah, I've been kicking around gear ratios also. Here's some info you may have.

I don't have those. I downloaded them. Thanks

 

[big a]

If it was mine I would go with the 3.5 first. That seems like a better RPM at cruise speed. With 3.25 you are barely into the turbo at 65mph plus 3.25 gears are very pricey. That is why I am going to try the 3.00 gears first to see if my mileage goes up.

Mine is running 2050 at 65mph and it is very happy but I think it is hurting fuel economy.

You are the 2nd person to tell me that . The speed limit down here is 75mph once you leave the city, which will be my cruising speed normally. I drive up to Amarillo and SE Oklahoma often, so other than just cruising through small towns, the cruise control will stay around 75. So after looking at my charts and taking this speed into account, what do you think??? I value your opinion as you've got real world experience with this engine! ;D

 

[big a]

I don't have those. I downloaded them. Thanks

No problem!!!

I don't remember where I found it, but it sure has some good info on it!

 

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Last wk I bolted up my transfer case to the tranny and discovered I had the width of a sheet of paper as clearance from the frame. I debated notching the frame, then, thought for a minute and remembered my rock crawler friends and bought a clocking ring. Well, I searched around and most of the different companies machined the same part so I bought one. Well, after installing everything I was disappointed that the first setting dropped me way too low! I could leave it, but then I'd have to modify my crossmember or fab a new one to clear the front drive shaft which was something I wasn't gonna do! So, now what??? ?:? After staring at the clocking ring, I noticed the spacing between the different settings was half that of the initial setting, which would put me where I want to be! So, I ended up buying a $70 template, sheesh!

 

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So, I removed the tail housing from the tranny, bolted up the clocking ring, now a template, and drilled out the 6 holes on my drill press. Even though it doesn't look like it, there is some meat between the holes.

 

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Then, I removed the old studs from the transfer case and bolted everything up. Success! I took it all apart again to address the original holes. Because the two holes are now so close together, the area is drastically weakened. So, I found some old 12mm head bolts from a Ford 4.6L. I tapped the holes on the tail housing, cut up the old head bolts to fit, slotted them for a screw driver and cleaned up the area with some JB Weld. The structural integrity of the tail housing is maintained, I won't have any oil leaks from the original holes and I gained the clearance I needed!!!

 

[big a]

I put it all back together to double check my work. I need to remove a little of the xfer case to increase the clearance a little more. I'm not sure why they cast that small hook in the case. It serves no purpose. I know the NP241 is found in 1/2 ton dodges and chevys, as well as jeeps and 3/4 and 1 ton dodges. Either way, I need to drill my crossmember so I can lock in the tranny where it sits, but other than that, the engine, tranny and transfer case are locked in!!!! Finally ;D

 

[big a]

My wife bought me a small blast cabinet as well as a belt sander for my birthday. I bought some glass bead so I can't wait to use it. Once I get the xfer case all cleaned up and blasted, I'll paint it with some Aluma Blast from Eastwood and install my new input for a diesel NV4500 as well as a Slip Yoke Eliminator Kit from JB Conversions! I hope to get this all done this wk! Then, I'll store it away and rebuild the old 4bt, rebuild the tranny, the axles, ahhhhhhhhhh etc...