In Slot Car Tech News

Front motor chassis

The front-motor in-line arrangement seems at first to be an unlikely drive train configuration for a slot car since it places the motor’s weight at the opposite end of the car from where it’s needed for maximum cornering grip.   However, with the introduction of strong neodymium traction magnets it has been quite successful on cars for plastic sectional track with steel contact strips. Fly has used the arrangement in all its models of front-engine cars. Scalextric uses it in models of two-seat front-engine sports cars to make possible the fitting of a full interior. Carrera, Revell-Monogram and MRRC have also made extensive use of it. Vintage slot car buffs will recall that Strombecker had front-motor cars as early as 1960, but these cars used a piece of rubber tubing to couple the motor to the drive shaft. Later versions used a very long motor shaft that ran all the way to the rear axle.

All the Fly, MRRC, and Scalextric front-motor cars use essentially the same endbell-drive motor and drive shaft assembly, which differs from one car to another only in having a longer or shorter drive shaft length and sometimes different connectors on the ends of the lead wires. The motor, shaft bushing, pinion gear, and spring coupler are interchangeable on all of them, as are the various mounting points in the chassis. (Drawing 1) Thus, if you have any Fly, MRRC, or Scalextric motor and drive shaft assembly you can use it in any of these manufacturers’ cars or in a scratchbuilt or kitbashed car using one of their front-motor chassis simply by lengthening or cutting the shaft as necessary. Since the shaft diameter on every motor currently being used in 1:32 scale front-motor home racing cars is .078” (2mm) you can easily make a longer shaft by getting a piece of .078” steel wire from the K&S metal rack at your local hobby shop and cutting a length to fit your car. In a Fly, MRRC, or Scalextric front-motor car you can use any endbell-drive Mabuchi S can (FC130) or other motors with the same external configuration. The motor will fit the chassis and the drive shaft and spring coupler will mate up with the motor’s shaft. In some cases, however, you may need to trim the motor shaft, either on the end that mates with the drive shaft or on the opposite end to clear parts of the chassis. This can be done easily with a Dremel Moto-tool equipped with a carbide cutoff wheel. Be sure not to let the motor shaft get too hot when cutting it, as this can damage the bushings.

Carrera and Revell-Monogram use the same arrangement but with a can-drive FC130 motor. R-M’s shaft bushing and pinion gear are compatible with Scalextric, Fly, and MRRC. Carrera’s shaft assemblies will also interchange, except that the shaft bushing is different. Again, shaft length differences apply.

Removing the drive shaft from the motor and reconnecting it is not difficult, but many people have trouble getting the spring off without stretching it. The key is always to push the spring off the motor shaft or the drive shaft, as shown in Drawing 2.

Place the jaws of your needle-nose pliers on the motor shaft between the endbell bushing and the spring coupler. Slide them along the shaft, pushing the spring coupler as you go. The coupler will normally come right off with only light pressure. Use the same technique to remove the coupler from the drive shaft as shown in drawing 3.

When it’s time to put the coupler spring back in place it just pushes onto the shaft. Fly and Scalextric motors have a splined shaft end to better grip the spring coupler. If you are installing a hopup motor, such as a Slot It V12, it won’t have the splined shaft end and may not fit the coupler tightly.   In that case, use a drop of medium CA glue in the spring coupler to hold it tightly to the shaft (Drawing 4). Don’t use the thin CA, as it can easily run into the shaft bushing and lock up the motor. Before using any kind of CA on a motor shaft or a drive shaft be sure to put a drop of oil in the motor and drive shaft bushings.     Be careful not to get any oil where the CA glue will go.

You can use a gear puller to remove the pinion gear from a drive shaft assembly without removing the shaft from the motor, but you have to remove the shaft before you can press a pinion back on. Once the spring coupler is removed you can use a pinion press on the drive shaft exactly as if it had a motor around it. If you do a lot of gear changes you will save time by making up several shafts, each with a pinion gear with a different number of teeth. Whenever you put the shaft assembly back together don’t forget to put the shaft bushing back on before reattaching the drive shaft to the motor shaft.

One of the biggest problems with some front-motor cars is the drive shaft bushing’s tendency to pop out of its mounting in a crash or even a hard spin. When this happens the pinion gear starts chewing teeth off the crown gear and after that the car never has a smooth, quiet gear mesh. We have heard from customers who have glued or wired the bushing in place, but we don’t recommend either of those measures because they make the bushing difficult to remove when you need to. There’s a better way, as shown if Drawing 5.   All you have to do is cut a piece of styrene strip or balsa about 1/8” by ¼” and glue the end of it to the bottom of the car’s body, interior tray or tub so the end of it presses down on the shaft bushing when the body is in place on the chassis. It will take a bit of cutting and trying to get the exact location and length needed, but once you get it right it will permanently end all problems with the shaft bushing coming loose without making it hard to remove.  Some front-motor cars come with an arrangement like this already in place.

With this information you should now be equipped to repair, replace, or modify the drive shaft assemblies on any of your front-motor cars with the fewest possible problems. Good racing!

Article and illustrations copyright © 1997, 2009 Robert M. Ward.  Used by permission.

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