RPM

Kitbashing a Ford Ranger and a monster truck into an Off-road Rock Crawler.

After years of attending off road rallies and wheeling my real Jeep, I finally got the inspiration to build a scale off-road rock crawler. Since no kits have been (or will ever be) produced of anything remotely close to such a niche subject, it would be up to me to kitbash and scratchbuild my own version of competition rock crawler.

In recent years, sanctioning bodies such as UROC, WEROCK and the XRRA have helped develop a new division of off-road competition. Rock crawling is not only a favorite pastime of many off-road enthusiats, it has become a popular spectator sport as well. Competitors drive anything from modified, street legal 4x4 vehicles to completely custom built, tube frame buggies. While the modified stock trucks may be more familiar to most, it’s the buggies that really have elevated the competitions to an unbelievable level.

These Unlimited Class buggies span a broad range of set-ups. Originally, large 2 seater, full size chassis with V8’s and military axles ruled the rocks. However in more recent years, the smaller, single seat, mid-engine competitors have taken a stand. Using anything from V8’s to turbo 4cyl powerplants and lighter, more traditional 4x4 axles, these agile buggies have made it much more affordable to be a serious competitor. In my case, this variety allows me to use some readily available kits to build a believable competition rock crawler.

Months earlier, while browsing the isles at one of my local “Mart” stores, I couldn’t help but pick-up a few closeout AMT/Ertl Teenage Mutant Ninja Turtles monster truck kits. Not having any desire to build these box stock, I figured they would make great donor kits someday.

A typical modern day rock crawler similar to the one I chose to model.

The first mockup with a few parts from both kits.

Another shot from the side shows off the aggresive look of the machines.

Well, someday came as I stared at an AMT/Ertl Ford Ranger kit on the shelf and realized I could combine it one of those monster truck kits for the basis of a rock crawler. The basic frame was the right shape and the heavy duty axles would be a perfect fit. Off to the workbench!

The upper chassis remains mostly as designed, sans the extra that can be trimmed before assembly. The lower chassis parts however are trimmed drastically and assembled in a different configuration. I constructed a simple jig to hold the parts in place while gluing the sub assembly together.

The moster truck chassis parts to be used.

The basic upper chassis after trimming it doen to size.

The cut-down bottom of the chassis in the "jig" to hold it in place.

This mockup shows the crawler taking shape, height looks better and wheelbase is longer.

A side view shows the "z"notch in the rear allowing for rear axle clearence.

The final ssembled chassis with all of the fit issues corrected.

Upon one of my early mock-ups, I noticed the rear of the chassis was too low and going to interfere with the rear axle. I notched the lower chassis tubes in two places allowing me to “z” the frame to gain clearance. Finally, a few extra lengths of .085 Evergreen rod were used to finish of the chassis/cage.

Moving on to the axles, some modifications were needed there also. The main axle assembly needs the outer axle pins trimmed off as shown. This allows for the wheel adapter to be inserted into the enlarged hole in the outer hub. Then, due to the off-set of the new donor wheels, the hubs need the locator pin for the steering linkage to be moved 1/16” inch. I simply trimmed the original one off and replaced it with more Evergreen rod.

This leads us to the actual steering linkage. First, a relief was filed in each end of the linkage to clear the wheels, Then the lower drag link was cut on one end and 1/8” was removed. To keep the assembly centered on the axle, the upper hydraulic rams were both trimmed in the same manner by 1/16”.

With the frame done and axles sized, I moved to the suspension arms. The stock kit arms needed some drastic shortening to make them fit. The picture shows the differences in length.

Below you can see the completed axle assemblies ready for paint. The nice thing is they still retain mounting pins to locate them on the chassis and to attach wheels to.

This shows the top modified axle comapred to the bottom stock one.

The fourlink arms had to be drastically trimmed down in length.

Here is the mocked up axle assembles ready for paint and weathering.

The stock V6 from the Ranger seemed to a reasonable fit for the heavy duty axles while keeping the over-all size of the buggy to a minimum. To fit it into the confined space, I removed the rear third of the transmission and mounted it directly to the transfer case. The entire assembly sits on the right-hand side of the vehicle so as to allow for better driveshaft clearance and weight balance. Some scrap frame, removed earlier, serves as suitable motor mounts.

I finished the engine in different shades of metalizer and added some wiring, plumbling, serpent belt and some solder headers.

Stock kit V6 show top, then with a transmission section removed bottom.

Scratchbuilt solder headers show the offset the engine will have in the chassis.

Some paint, wiring and a rubber serpent belt bring this little powerplant to life.

Last but not least are the body panels. I want my crawler to have some resemblance to a factory vehicle, so I narrowed the hood and grill from the Ranger kit. The rest is simple sheet styrene panels cut from cardboard templates.

At left, stock Ranger hood and grill, to the right, the modified hood and narrowed grill.

Just a teaser shot, as it sits currently.