In Mercedes-Benz, Mini Big Rigs, August 20219 MinutesBy Carl KirkbeckSeptember 24, 2021

This month, things start to take shape, with the completed chassis receiving a coat of paint, installation of the engine and transmission, and fitment of wheels. At last, we begin to see a tractor unit form.

We’ve worked our way through the preliminary stages of steps 5 and 6 and prepared the chassis for paint by assembling and fitting the major components, simplifying the painting process. If you were to paint each piece first before assembly, you would have to remove the paint from all the glue contact points for correct adhesion which, in turn, increases the risk of glue stains in the fresh paint. Assembling as much of the chassis first is the tidiest and most efficient way forward and is generally the approach taken in actual truck assembly plants.

Before we paint the chassis, it is important to carefully apply masking tape to the areas we do not want the spray paint to cover, such as the axles, where the wheels are fitted. If these were coated in paint, you would find the wheels will most likely not slide on at assembly or rotate as they are supposed to, resulting in remedial paint removal.

Painting a chassis with a brush is very fiddly, time- consuming, and compromises the potential finish, so spray paint is highly recommended. With a piece of fine wire, hang the chassis at a good working height in an open, well- ventilated space, such as the branch of a tree in the back yard – don’t get overspray on Mum’s variegated monstera.

1) Careful application of masking tape to specific areas – for example, the axles – to exclude them from a coating of spray paint saves a lot of heartache at final assembly.

2) Using a piece of fine wire to suspend the chassis in the air achieves an ideal working height and provides great ventilation. Remember to follow all safety precautions listed on the spray can.

3) Careful application of minimal glue to the tip of the axle and surface of the retainer rings – 89A for drivers and 113A for steerers – is required to ensure that the wheels still rotate freely on the axle. Remember to allow this glue to dry thoroughly before fitting the outer wheels of the dual set.

Tamiya TS-29 ‘semi-gloss black’ is the colour of choice for our project. Be sure to read all the precautions on the spray can and follow the safety instructions listed. With the chassis attached to the fine wire, you can rotate it to ensure the coat of paint reaches all the inner details. With spray painting, generally use short sharp blasts of paint, keeping the can moving and continually rotating the model to not build up the paint in one area. A gradual build-up of light dustings achieves the best result and ensures the detail is not buried. Once happy with the paint coverage, leave the model to dry thoroughly before handling.

Once dry, removing the masking tape reveals the bare plastic of the diesel tank ready to receive a coat of Tamiya XF-16 Flat Aluminium for a realistic finish.

Looking at steps 5 and 6 again, we see the breakdown of the assembly and attachment procedures for both the rear-drive wheels and front steerers. Starting with the rear drives, we carefully slide the inner dual onto the axle, ensuring that the wheel freely rotates (some minor filing/sanding to the axle surface might be required here). The next step fits the retainer rings – 89A – and requires careful application of glue. First set 89A in place dry with no glue. Then, once happy with the fit, apply the minimum amount of glue to the front face of 89A and the axle where it protrudes through 89A. Allow this glue to dry thoroughly before fitting the outer wheel, as you may find that the glue makes contact and freezes the wheel in position. Once the glue on the retainer rings (89A) has set, apply the minimum amount of adhesive to the surface of the hub stem of the inner dual. While this glue is wet, slide into position the outer dual over the hub stem of the inner, this will create a bond between the two individual wheels, creating one solid unit while still allowing the wheel to rotate freely on the axle.

The fitment of the front steerers in step 6 is a little more straightforward. Apply the same methodology as the rear drives, with careful application of minimal glue to both hub retainers (113A), as well as the tips of the stub axles. Careful attention here will ensure the finished wheels can still rotate on their axles.

Next is the final installation of the completed engine and transmission assembly. This is a straightforward procedure. There are two tabs at the front of the engine, one on each side of the engine block, which represent the engine mounts on the real truck. These slot onto a pair of matching locators on the inside of the chassis rails. On the underside of the transmission, there’s a locating pin that marries to a location on the centre of the transmission cradle crossmember.

Our subject matter, Pilkington Automotive Glass Mercedes-Benz 2244, driven by Ken Kirk in 1992.

First, ensure that you have carefully removed the paint from these surfaces so that the glue can adhere correctly. Now, apply a little glue to the three location points on the engine and transmission assembly and the matching points on the chassis. Next, slide the engine and transmission assembly into place while holding the front driveshaft – 89A. This will sit in place on the completed model without glue as it has two solid pins, one each end, representing the transmission and front differential splines on the real truck. To save fingers from being covered with a gluey mess, set 89A into the front of the diff as you slide the engine and transmission assembly into place on its pre-glued locations. This will also allow rotation of 89A as required to achieve correct drive-line geometry.

Now fit the fifth wheel onto its frame. This will easily sit on the two pivot point towers of the frame without glue. I would recommend not fixing this in place now as you may want to build a trailer later and need this pivoting movement to accommodate the kingpin.

Now, with a finished rolling chassis, we are well on the way to a completed tractor unit. Next, we will assemble and fit our rear guards over the drive wheels and begin the process of piecing together the interior for the cab.