Choosing, cleaning and getting started
The most important part of this process will be the choice of parts. Spare parts are the key to a smooth, fast MT. If you only have two or three, don’t fret. We can get a good one out of those. It will require swapping and switching parts to find the combination that works for a particular application.

I will assume we are building a road course chassis for plastic sectional track. The key here is drivability—meaning a SMOOTH drive train.

Let’s start at the beginning. There is a substitute for horsepower, and it is smoothness. A well-balanced motor with a flat comm. plate is a must. If you don’t have the ability to balance a motor, a good stocker from Alan Galinko is in order. The Mean Green stock wound he sells is almost perfect. If you prefer box stock, I think he will do red with gold wire arms the same way.

After taking care of the motor, the next step is the brass drive gear. Make sure it is flat and free from nicks. Line up all the drive gears you have next to each other. You will notice they are not all the same. Try to find a “deep tooth” gear that is nick-free on the teeth, and set it aside.

Next, take all the idlers you have and make a pile. Guard that pile with your life--it will be very important later.

Now we come to the only major design flaw with this chassis. The dreaded riveted cluster gear. This is the biggest culprit in most bad drive trains. There is only one way to check it: Find a chassis with a good crown gear and straight axle and use this to test your plates. Put them on, one by one, and find the one that feels the smoothest as you rotate the axle. If they all seem to be rough, inspect the crown gear, making sure it is not running out, laterally. You will also find that some plates fit better than others on your test chassis. Keep this in mind.

Now that we have our two or three plates and our motor picked out, let’s find a chassis frame. Things to look for in this are, in order of importance:

Brush holes intact and round.
Many chassis, in their lifetime, got over-oiled. This was the cause of the brushes getting hot and melting the brush holes, making them bigger than normal. This would not be a problem except that the spring must sit properly under the brush. If it doesn’t, the brush will rock the wrong way to the rotation of the arm.

Axle holes sized properly.
Because of the design of the chassis, these holes often wore excessively and caused the crown gear to be out of position. Our club allows for bushings in these holes. If we didn’t, we would run out of chassis, that’s how prevalent this problem is. Concentrate on the left rear hole. This is usually the one that’s worn the most.

Chassis straightness.
Just as in T-Jets, the AFX chassis can--and will--be racked from corner to corner. The object is to find the least amount of warping as possible. This can be checked with a set-up block or a glass coffee table.

Next thing to do is to find the best set of magnets.
If you have a trick new magnet-checker you’re in good shape; if not, you just have to use your head a little more. I use a socket from my socket set to test the amount of pull the magnet has in the concave portion. When you find a good magnet, set it aside. Look for one of each, then test the down force side of the mags. When you’ve found a couple of sets that are better than the others, it’s time to get out your chassis.

This is where it gets interesting. Fit the mags and try the “rollover” test. Find an old motor and plate, and assemble the chassis, plate and idler. With the mags in, slowly rotate the rear axle with your fingers. If the mags are “matched” the arm will flop from the front mag to the back on every pole. If there is one mag too strong, the arm will flop to the same mag every time an arm pole gets to it. Also try to flip the magnets upside down, and then try them one up and one down. When you’ve found that good set, don’t forget to mark it, and set it aside.

The only thing left to do in the parts department is find a true set of wheels and axles. If we are going box stock, I strongly suggest a good wheel/gear puller. If you don’t have one, fingers will have to do. I disassemble my rear ends and choose the axles with the best finish and spline. If the chassis you have chosen to use already has a good wheel set, then try using it to get started.

If you want the best alternative to stock , a set of hobby pro .250s double-flanged is hard to beat. The ones I found are purple. To go with these, a Tomy super G+ rear axle is the standard axle in my race chassis.

Part II: Assembly and Adjustment.