Calming Down the MRRC Cobra

As beautiful as these cars are, one thing that really keeps me from giving them much wanted track time is the crazy fast 28,000 RPM Red can Motor that they are equipped with. In this article I will be replacing the factory motor with a (Scalextric C8421) S Can SP Motor 20K RPM. This motor can be found in any Scalextric Nascar- IRL type slot car.

We will start by removing the body with the 2 screws. After the body is free I used a small screw driver to remove the magnet. Then using a soldering gun heat the solder where the 2 lead wires are connected  and lay them to the side.

Here you can see I have removed the motor & drive shaft from the chassis.This gives a comparison to the stock motor and the new (used) Scalextric motor.


Removing the drive shaft/spring from the motor. To do this just use a pair of wire cutters and place them just behind the spring. Slowly and easily pry towards the spring. This will not take much pressure and the spring along with the drive shaft will slide off the motor shaft.

Now with the drive shaft removed, use a pair of pliers and grab the drive shaft from the end with the pinion gear and use some pressure to press it on the replacement motor. You may have to test fit until the required length is found. Make sure the drive shaft does not make contact with the center of the crown gear or it will bind.

After the drive shaft has been installed, the motor and drive shaft are snapped in place in the chassis. Also the lead wires can be re-soldered to the motor.


I`m now ready to start tuning the chassis with some lead weight. Since I`ve already done this on another Cobra, I`ll repeat the process on this one. I took the magnet I removed earlier and set it on a piece of lead.  Traced around the magnet with a Exacto knife, and cut out the piece. This will fit right in the spot the magnet was removed from. I also measured the bottom of the chassis where the motor sits and cut a piece to be glued in. I found that with the height of the chassis from the track this was a good placement to get some weight closer to the track.

Hot glue was used along both sides of the motor just to eliminate any twisting. Also a couple drops were used just to be sure the rear lead stays in place.

The Cobra also has allot of up and down slop in the guide. To remedy this I used 7/32 Styrene tubing and cut a piece to size. It will snap right over the guide and fit nicely.

This is one beautiful slot car. My reasoning behind this modification is simple. I bought this car because it has always been one of my favorite race cars. And I wanted to watch it go around my track and enjoy it. With the motor it was equiped with, not only could I not have fun with it, but at the speeds it was capable of, if it ever desloted. I`m sure allot of the fine details I enjoy so much would have been destroyed. Now it will see plenty of track time !!!!!

Back To Home