Lessons Learned from My First Bug Out Truck – Part 2, by H.J.

(Continued from Part 1. This concludes the article.)

Using one side of my mechanic friend’s two-car garage, the gasoline engine was removed and the 4BT was prepared for test fitting by pressure washing the engine and scrubbing down with degreaser. One of the top killers of diesel engines is high exhaust gas temperature (EGT), which can occur under hard use and heavy loads and can melt the pistons and cylinder rings. To monitor this temperature, the turbocharger was also removed, the exhaust manifold was drilled and tapped for an aftermarket pyrometer, and the turbo re-installed. It is important when monitoring the EGT to do so in the manifold and not in the exhaust pipe due to heat loss through the turbo. To ensure that the engine was receiving adequate fuel, the banjo bolt connecting the lift-pump hard fuel line to the fuel filter housing was removed and then drilled and tapped to accept an aftermarket fuel pressure sensor.

Since the manual transmission was being retained, a universal flywheel tachometer adaptor from Dakota Digital was used to work with the original tachometer. It is important to get an accurate count on the number of flywheel teeth before bolting the engine to the transmission (ask me when this was found out), as the adaptor has a control box which requires you to set a series of switches so that the signal to the tachometer is correct. Once this is done, the unit works flawlessly.

Following the recommendation from the 4BTSwap web site, the stock diaphragm lift pump was replaced with a higher-performing piston-style unit. The engine was than lowered, dummy bolted to the transmission, and blocked in place. Using cardboard, we mocked up motor mounts which were cut out of scrap 1/4″ steel plate by using a handheld oxygen-acetylene torch and stick welded together. The resulting mounts were hardly show-worthy but have proven to be more than sufficient over the years.

The engine was then installed properly and bolted into place. The existing fuel tank was re-used after being dropped, drained, and rinsed out with diesel fuel several times. The stock fuel line was reused and we left the in-tank fuel in place but removed the fuse from the circuit. It is important NOT to use the in-tank fuel pump because it operates at a much high pressure than the 4BT fuel system is designed to handle on the incoming side, which can blow out seals in the lift- and injector-fuel pumps.

Exhaust Work

Moving onto the exhaust, the downpipe was slightly modified to clear the passenger side firewall-transmission tunnel seam. The downpipe was temporarily connected to the existing exhaust system by using flex pipe. A local exhaust shop later replaced the flex-pipe with a correct and much more sturdy exhaust pipe.

The engine is turned off and on by an electromagnet plunger valve located on the side of injector pump and looks somewhat like a spark plug. Energizing the plunger valve causes a spring-loaded plunger to retract from the fuel passage allowing fuel to flow. De-energizing allows the spring to expand, pushing the plunger into the fuel passage which blocks the fuel flow and shuts down the engine. We located an ignition hot circuit in the engine bay fuse box and ran a wire from there to the valve, allowing the engine to be shut down using the ignition switch.

An important note is that if the ignition system of the vehicle failed to work, the plunger valve can be removed with a crescent wrench, the plunger and spring removed, the valve body re-installed, and the vehicle will run. This condition will require the engine to be shut off by intentionally stalling the vehicle.

The entire swap process took about two weeks of on-and-off work in between my friend’s other customers.

A Few Glitches

As expected, several small leaks and loose bolts were found when the 4BT was started and test-driven. At idle the diesel has a pronounced rattle and vibrates the entire truck. It has been compared very often to a hardware store paint mixing machine, which in all honesty is pretty accurate. Anyone who has spent time around older, all mechanical diesel equipment will be familiar with this characteristic, with a four-cylinder engine it is more so. On the road at operating RPMs, the engine smooths out and the vibration goes away.

Acceleration is marginally better but the truck holds speed climbing hills much better, rarely requiring downshifting. If desired, additional horsepower can be made by modifying the fuel injector pump. I have left the engine in stock tune and have been very happy with it, even when pulling a loaded two-axle car-carrying trailer. Fuel economy was a drastic improvement: an average of 25 MPG on long 55-60 MPH runs without a trailer. Running at Interstate speeds lowers the average by 2-3 MPG.

After several years and +100,000 miles, I have no regrets with this conversion and I would do it again.

Suspension and Driveline Work

With the engine conversion complete, the suspension was addressed next. The rear leaf springs were replaced with a custom set built by a local spring shop and included heavy-duty overload springs. This lifted the rear of the truck approximately 2”. Combined with the lowered nose from the additional engine weight, the truck had a very raked stance. The front suspension was lifted up using a set of heavy-duty coil springs from BroncoGraveyard.

The truck performed well in this state for almost a year until an off-road adventure in heavy snow resulted in a broken front axle shaft. This mishap also showed that there was no place on the front of the truck to attach a rope, strap, or chain without having to crawl underneath and wrap it around the front axle. Definitely not an enjoyable experience to do in 12” of snow. Both axle shafts were replaced with heavy-duty off-road shafts from Bronco Graveyard. A front mount trailer hitch with recovery loops was found on eBay and installed. To increase the trucks off-road performance, a PowerTrax drop-in locker was installed in the rear axle. I had the opportunity to test these upgrades over several heavy snows that same year and the truck performed nearly as well as my wife’s Rubicon Unlimited Jeep.

I have operated the truck in this form for several years now in this state and have been very happy with the results. With nothing more than routine maintenance such as changing the oil, filters, and brake pads, the truck has been very reliable and attracts a lot of attention at car shows and around town. Future upgrades that I am considering include a receiver hitch-mounted winch with front and rear plug-in connections, a CB radio with side-band capabilities, an enlarged fuel tank, and possibly a steel off-road bumper and cloth camper shell for protecting cargo.

In closing, I would highly recommend that anyone looking to build a Bug Out Truck/Vehicle considers using a 4BT or 6BT Cummins engine. You will not be disappointed.

For those that are interested in this type of conversion but would want a smoother, more refined engine and are not put off by having computer controls, Cummins has responded to the 4BT conversion “craze” by now offering the R2.8 crate engine. This engine is smaller, lighter, and smoother operating than the older 4BT while providing similar horsepower and torque. Coming with its own stand-alone engine control computer, the R2.8 appears to be — at least electronically — a very simple engine to install. I have not had the opportunity to have hands-on experience with this engine but do have plans to install one in my wife’s Rubicon Jeep Wrangler Unlimited when time and money allows it.


  1. Thank you HJ for the informative and inspiring post. My project, of rebuilding a ‘98 AM Gen H1 wagon seems daunting, but this winter hopefully ~ it will be at a place to roll out in spring. This is one of those projects that is teaching me lessons in life which I should have learned much younger. Loved the read.

  2. Great project with lots of good information. Wow! I’m always impressed when someone grabs the bull by the horns and actually does a project like this. Just wondering what adapter was used between engine and transmission and was original clutch utilized. Have seen people fabricate a transmission adapter but sure makes things easier if one is ready made to purchase. Also was some type of cold start aid installed such as intake heater etc. Just thinking of winter starting for those of us that live in colder climates.

    1. The adaptor is an actual Cummins-made part. Two adaptors were made, one fits a small block Ford bellhousing, the other is a small block Chevy. I used a stock clutch.

      I ran the Cummins for several years w/o any type of heater or starting aid and got it started in 0* weather, however I would not recommend it. A freeze plug block heater is an easy install w/ the engine out of a vehicle. A universal water heater can be spliced into the heater core water lines for an easy in-vehicle install. Cummins B-Series do not have glow plugs but do use an air intake heater grid to aid in cold starting. I installed this later on along w/ a 2nd battery, and operated it off of a push button. If you see a lot of below freezing weather, I would highly HIGHLY recommend some type of heater for the fuel system, either on the fuel filter or on the fuel tank. I’ve not had issues w/ fuel gel with the Cummins but have had a lot of problems w/ a Ford 6.4 even w/ triple dosing the fuel w/ chemical anti-gel.

  3. Interesting swap. I’ve always been a fan of cummins engines, having rattled around behind them for some 3.5 million plus miles.
    Not that long ago I installed a diesel in a 1954 Willys flatbed PU and considered the 4BT but decided against it due to weight issues. Settled on a 1985 Mercedes 5 cyl. turbo diesel, the last series that was completely manual & vacuum controlled. Replaced the running gear with 2003 Jeep axles, tranny & transfer case. Making a long story short, after 2 + years of work I ended up selling it as the cab turned out to be too small for me to drive comfortably.
    I’m a gear head at heart! Next project along these lines is a tractor, of garden tractor size with a 4 cyl, Yanmar turbo diesel. I got the eng.(s) already and need to put em to work….. Ahh, the follies of men!

  4. The engine swap is a big project, even for the skilled mechanic. … The Cummins Engines are ~time tested with parts readily available. [Plus a lot of free information on the Internet.]
    … … + In the maybe hard-times in the future, it might be possible and ~legal to make White Lightning, Idaho Potato Squeezin’s to power a diesel engine.

    Wikipedia says this:

    The Cummins B Series is a family of diesel engines produced by American manufacturer Cummins. In production since 1984, the B series engine family is intended for multiple applications on and off-highway, light-duty, and medium-duty. In the automotive industry, it is best known for its use in school buses, public service buses (most commonly the Dennis Dart) in the United Kingdom and Dodge/Ram pickup trucks.

    Since its introduction, three generations of the B series engine have been produced, offered in both inline-four and inline-six configurations in multiple displacements.

    The 3.9L/4BT Cummins is an engine in the same family as the 5,883 cc (5.9 L; 359.0 cu in) Cummins diesels. The 3.9L/4B is an inline four-cylinder naturally aspirated or turbodiesel that was popular for many step van applications, including bread vans and other commercial vehicles. Additionally it has seen broad usage in agricultural equipment. It has also gained popularity as an engine swap into smaller trucks.
    “The U.S. Renewable Fuel Standard requires more biofuel in the U.S. transportation fuel mix.
    Biodiesel is a biofuel that can contain used cooking oil, known as yellow grease.
    As much as $75 million in yellow grease is stolen each year, with thieves collecting around 25 cents a gallon.

    It sounded odd when a Virginia man was arrested recently for pumping hundreds of gallons of used cooking grease from a dumpster outside a Burger King in the Allendale Shopping Center. But this isn’t the first time used cooking oil caught thieves’ attention.

  5. I won’t pretend to be remotely mechanically inclined (I’m no “Malorie”), but this series of articles really made me think about what would happen if SHTF and our trusty Toyota needed maintenance.

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