Detroit Metro Soap Box Derby

DMSBD Tech Tips
Construction Tips for a First-Time Car Builder
Article 1: Getting Started - by Ian Carsten

Although it is tempting to begin building your car as soon as you receive it, you should first inspect and inventory all the parts to be certain that the correct number of parts of each description and listed dimension are present and in usable condition. It is unfortunate that sometimes parts are missing or are not usable due to some manufacturing error. If anything is missing or defective, then you need to contact the AASBD as soon as possible to arrange for replacement.

You should check that every part listed on the parts list, which came with your car, is present by identifying it, counting how many pieces are present, and checking it off from the list. The next step is to check all components for usability. For example, the machine screws should have fully formed threads. It’s easy to check this by simply screwing on a nut of the appropriate size—it should thread on easily. You should pay particular attention to the axles and floorboard since they are the most important components.

It is very important to measure and verify that both the front and rear kingpin holes are on the longitudinal centerline of the floorboard. To check this, simply measure the distance from the center of each kingpin hole to the right and left edge of the board. Both dimensions should be the same within 1/32-inch (or 1 mm). If this dimension is not the same on both sides (within the stated limits) then the triangulation procedure shown in the plans to adjust the rear axle 90 degrees to the centerline of the floorboard will not work. A floorboard whose kingpin holes are more than 1/32-inch or 1 mm off the centerline should be returned for replacement.

The next item to check is the axles. When you unpack your axle set you will notice they are covered in thick dirty oil. They are packed that way to prevent rusting. Clean off the oil with paper toweling or rags you are willing to discard. You’ll never get them completely clean by wiping since the surface is porous and holds the dirty oil in pockets. A good way to get them really clean is to wipe them off with a rag wetted with mineral sprits. Then wipe them dry. Now give them a really good scrubbing with warm water and a steel wool soap pad, such as SOS or Brillo. After you rinse them off and wipe them dry, they should be bright and clean.

The axle sets are the same for each of the three kit cars, stock, superstock, and masters. They are fabricated from 3/4-inch cold rolled steel square stock. The axles have the AASBD logo and year of manufacture stamped into them. Verify these are present; otherwise they are not legal for competition. The ends have been lathe-turned to form 1/2- inch diameter spindles for wheel mounting. Use the plans to identify which is the front and which is the rear axle. Be sure you have one of each. They are drilled slightly differently in that the rear axle has two additional vertical holes to attach the stabilizer bars (also called radius rods) to a stock car, and two additional horizontal holes for the axle adjuster screws on both the superstock and masters cars.

Inspect the axles carefully to verify the center hole for the kingpin is within 1/16 inch of the center of the axle, lengthwise. Fortunately, both the kingpin holes in the floorboard and the ones in the axle are usually well within the stated tolerance. The wheel-retainer clip holes on the ends of the axle must be perpendicular to the kingpin holes. Quite a few 2001 axles were shipped with these holes drilled parallel to the kingpin holes (i.e. vertical in assembly). If you get such an axle, send it back for replacement. Now you should check the length of each spindle and the position of the wheel-retainer clip hole. To check this, put a z-glass wheel, two wheel washers, and the wheel clip on each spindle. You may not always want to use two wheel washers, but you need the clearance to do so if necessary.

If you have read the literature on performance enhancement, you will probably want to polish the spindles. This is a good time to consider how best to do so. Spindle polishing can be done with the axles mounted to the floorboard, but it is much easier to do so before they are mounted. The details of spindle polishing will be discussed in an upcoming article in this series. Lets assume that you have chosen to polish your axles before mounting them, and that task is now done.

Once you are sure all of the parts are present and in good order, then you should think about sealing the floorboard. Floorboard sealing isn’t required. However, it makes for a much more workman like job, looks better, tends to stay clean, and prevents the board from warping due to humidity or if the board gets wet. Current rules state you may use either automobile body wax or tung oil to seal the floorboard. It doesn’t take too much thought to realize that applying car wax to unfinished wood is not practical. Tung oil, pressed from the seeds of the Asian tung tree, is the major component of many varnishes and paints. The manufacturer prepares it by heating to transform the raw oil into a deep-penetrating, waterproof varnish. It is available from most hardware stores as a commercial sealer/finish and is commonly sold under such brands as Homer Formby’s, Minwax, Sherwin-Williams, Waterlox, and so forth.

The best way to support the floorboard for sanding, sealing, and building the car is on a pair of sawhorses. Also, if you want to protect the relatively soft wooden surface of the board during finishing and construction, you should fasten some soft material to the tops of the sawhorses to prevent damage. Strips of carpeting are ideal for this. Just be sure that no nails or screws used to fasten the carpet to the sawhorse can contact the floorboard. An alternative to this is to glue the carpet to the top of the sawhorse. Sawhorses modified in this manner will be useful later when any repairs, or adjustments are to be made. When the sawhorses have been prepared, you are ready to begin.

Although the floorboard is reasonably smooth as manufactured, you may wish to first sand it as smooth as possible, especially on the bottom surface for maximum aerodynamic efficiency, with progressively finer grades of sandpaper before sealing it. Given the size of the board, an electric sander can save lots of time on this job. Before applying the sealer, carefully read and comply with the manufacturer’s directions. Most drying oils, such as tung oil, require very thin coats, and must be allowed to dry and harden before applying subsequent coats. This usually must be applied by rubbing in with a small piece of cheesecloth for best results. If you brush it on, it may take a week or more to dry and leave unsightly runs or drips. Once the floorboard sealer is dry and hard, which may take several days after the last application, you are ready to begin assembly.

The assembly plans are reasonably well written and ample illustrative drawings are provided, such that the assembly should be fairly easy. If you’ve never built a kit before, then it might be helpful if you could make arrangement to consult an experienced builder for advice should you run into difficulties. This probably won’t be needed, but it is reassuring to be able to make a telephone call for some quick advice if wanted.

Only a few fairly common, inexpensive tools are needed to build a derby kit car. It is likely most builders will already have them. Also, there are a number of tools that can make certain assembly and setup tasks much easier and /or precise. You may have some of these already or you may wish to purchase or borrow them. Further, there are a few rather expensive derby-specific tools, which a beginner will not have, and can usually be borrowed or be used at construction clinics held by your local derby organization.

The common tools needed to build a derby kit are: two 7/16 inch wrenches, two 1/2 inch wrenches, two 3/8 inch wrenches, a large flat-bladed screwdriver, #2 Phillips screwdriver, pliers, hammer, hacksaw with fine-tooth blade, 5/64 inch Allen wrench, mill file, and an assortment of emery paper in medium to fine grits. At least one of the 7/16 inch and both of the 3/8-inch wrenches must be the open-end type. These tools will enable you to do the basic assembly tasks.

The less common tools that will make the job easier are: a pliers-type of cutter designed for cutting hard wire rope (i.e. 1/16 inch brake and steering cables), a set of trammel points and a roughly 72-inch beam to mount them on, an inch-pound torque wrench and 7/16 inch and 1/2 inch socket wrenches to fit it, a pair of 2-inch c-clamps, a steel tape scale (inch or metric), a combination square with a 12 inch blade, a center punch, machinist’s layout scriber, a roll of black plastic electrician’s tape, an electric drill motor and an assortment of bits. Many of the tools in this category can be borrowed or used at your local derby’s construction clinic. Also, it is prudent shop practice to wear a pair of safety glasses when using any tools, especially sharp edged or pointed ones, and is absolutely mandatory with any type of power driven tool.

The only derby-specific tool that you will want to use is the dial indicator-equipped spindle alignment gage, a pair of axle support stands and a pair of spindle adjusting wrenches. Currently, these special tools cost $325. Unless you become a committed derby racer and travel the rally circuit, you probably should not purchase these. Rather, you should borrow them from someone who already has a set or use them at one of your local derby’s clinics.

This concludes Article 1: Getting Started

Proceed to Article 2: Spindle Polishing

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