Capo JK Max Project

Page 1: Building the Engine

I have rarely been so excited waiting for a package to show up. The box is actually smaller than you'd expect and there are no pictures on the outside to tell you what's inside. Once you open the box you are greeted by a foam insert laying out all the primary metal body panels with the prebuilt axles to either side. Beneath the foam is a smaller box containing all the piece parts. The small empty slot you see in the foam is where the USB flash drive was which contains the video instructions.

Here is everything that was under the foam. There are 5 tires (including the spare) and many bags of metal parts. There are only a couple of plastic parts trees. In the right hand image you can see the large number of individually bagged hardware types. Everything appears to be stainless which is good for threading into aluminum. Since nearly every screw and bolt threads into metal, it is really important to use thread lock everywhere or this thing will just fall apart.

Here are the parts laid out for Step 1 which involves starting the construction of the 2-speed transmission. Everything you see is metal. The bell housing and transfer case housings appear to be cast aluminum. The shafts and gears are steel. The transmission gears are all helical. This includes the pinion gear which you can see on the right. I've never seen a helical pinion before. Capo's marketing material indicates that mating gear pairs are made from different types of steel. This is exactly how it is done in industry to prevent too much tooth wear. I chose a Holmes Hobbies brushed motor which has really showed me how good it is possible for a brushed motor to be. For trail trucks and crawlers, I still prefer brushed over brushless for the feel. Even sensored motors don't come close.

The motor is installed to the rear cover of the engine block. The front cover has a mesh screen to allow airflow through the otherwise closed block for cooling the motor.

Now we build the transmission housing which is a thing of pure beauty. It looks just like a full scale version. First you install the rear cover to the bell housing and then the t-case front cover is installed. In this photo I actually installed the t-case backwards; it should be facing to the left. I didn't figure it out until I tried to install the engine later.

Here's the primary shaft. The driving ring is in the middle and uses drive dogs to engage the gears on either side. You can see the helical profile of the teeth in these images.

This is the shift fork which engages the driving ring to shift gears. It slides back and forth using external servo input. On the right the primary shaft and shift fork are installed into the housing. I have not greased anything yet at this point. This is an unusual gearbox design in that the primary shaft is also the output shaft. The gear you see on the far right is the spur gear which will mate with the motor pinion. This gear rolls freely on the main shaft as do all the other gears. The smaller gear just to the left of the spur is integral to it. It interfaces with the secondary shaft which spins at a constant rate relative to the motor. The two output gears on the secondary shaft transfer torque back to the main shaft gears which then rotates at one of two ratios depending on which gear is engaged. The driving ring is the only thing locked to the main (output) shaft so that whatever it engages drives the output. Clever!

Now we install the straight cut gears in the transfer case. Since there are an even number of gears, the forward and rear drive shafts rotate in opposite directions which prevents torque roll. In the right hand image I have finally noticed that I installed the t-case backwards and have corrected it. This completes Step 1.

Step 2 adds a bunch more parts to the engine to button everything up. In the picture on the left you can see the first plastic parts which include the valve covers and the intake manifold. On the right you can see the transmission secondary shaft.

The secondary shaft inserts into a bearing on the far end and is supported by a bracket housing another bearing on the other. The next thing to do is install the shift servo. The shifting system uses a micro servo which is housed inside the engine case so it won't be seen. It takes a little fiddling to get it adjusted. You want to get it right now because it will be very difficult to access later.

From the bottom you can see both transmission shafts and the shift fork mechanism. I've also added the first engine block section which covers most of the motor and shift servo. From the bottom I then install the oil pan which is also metal.

To finish up the engine I need to add the front block section and then the plastic top bits. I painted the valve covers in the same color as I'll later paint the body, and the intake manifold is flat black. The last picture also shows the optional pulley system which I'll take about later in the upgrade section. I wanted to add it now because it is much easier to install when the engine is apart anyway. The final completed engine has quite a few wires sticking out the back including those for the motor, the shift servo, and the pulley motor.

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