The Magazine For Slot Car Enthusiasts

Ed Harris - Smoothing Out Those Thunderjet Chassis
The flat toothpick also lets me force a bit into the bottom arm hole and the lower cluster gear shaft bore.

After I have a kind of "moat" of Simichrome built up, I use a Q-Tip to drip Brasso into the "moat", and once everything is smoothed up, I take it to the sink and scrub the chassis with a toothbrush and Liquid Lava, disassemble, and run through the UC. The last few nights I've been experimenting with switching the rail polarity on the dyno to reverse, then flipping the chassis upside down (it still runs "forward" this way). Then I put a drop at a time of Brasso using the Q-Tip, in the brush bores.

It seems to be actually polishing the tops of the brushes and the bottom of the armature at the point of contact.... I am getting chassis fairly regularly that will spin the dyno above 500. I do this after everything else, and it means I have to run them through the UC again, but 500! Man, six weeks ago, the fastest TJ I'd ever seen was 460.

The only part that even sees a file is the idler gear on mine. I try to round off the square corners before I start the lapping process. The other gears really don't move around or drag on their corners, unless something is very wrong/crooked.

You need to get a dropper bottle (the one I use had cat medicine in it originally, so maybe a pharmacy or veterinary supply might have 'em). Mine holds about an ounce of liquid, and I fill it with LifeLike Track Cleaning fluid. It is the absolute best for flushing out the gearplate gears/bores with the motor running, as well as being better "comm drops" for the TJ than any of the "real" comm drops from Trinity or RevTech (hobby shops that sell R/C cars have comm drops). It's amazing stuff, you can hear the motors spin up faster, and a few applications really helps seat the brushes. It cuts the amp draw and raises the dyno reading! For this use I've also tried AJ's TNT, but so far the LL is the top stuff. It also helps flow the light lubes down into the gearplate shaft bores. Neat, you've gotta try this stuff.

One thing to be aware of with the Ultrasonic Cleaners is that the solutions that have Ammonia (like what I'm using) will soften the copper of the brush springs and armature comm plate if these parts are left in the solution a long time, like overnight. The brush springs can get so weak the chassis is useless, and if the comm plate copper gets too soft, you'll get weird "3-bladed prop" wear patterns, and the armature will have to be replaced. Just try to limit the time in the solution to no more than 30 minutes at a time, and be aware of the accumulated time spent in the UC.

In this article Earl Harris is going to tell you how to set up a stock Thunderjet by lapping the Chassis:

Use a flat toothpick to apply some Simichrome around the armature gear and dab some on the hole in the bottom of the arm, with no idler gear installed. Run the motor forward and reverse, reapplying when the motor starts to squeal. You can use a few drops of LifeLike Track Cleaner to help dissolve the Simichrome so it'll flow under the top gear and around the arm shaft at the bottom, easiest to do the bottom with the chassis inverted.

After a while of doing this, you'll get used to when you should stop. Once these two most important spots are done, you can clean everything really good in an Ultrasonic Cleaner (UC) and start over with the idler gear on but no rear axle installed yet.

Ultra Sonic Cleaner
When the motor starts to squeal after the second dousing, stop, disassemble again, and run it through the UC for at least 30 minutes. It is important to get all the polish out of the car, or it will continue to wear, and that's bad.

Reassemble, lightly oiling all the bores, idler pin, axle holes, and run the chassis. When you get everything "right" you will hear a big difference in the speed of the chassis. If you want the last "N"th degree, flow some Brasso around the gear train, bores underneath, axle friction points, and listen to the motor.

Thunderjet Chssis
Thunderjet Chssis
Reassemble, lightly oil, and spin it up under power. To verify that all the polish is out, drip some LL TC on the top gears, if the foam is grey, continue dripping on the LL TC until it is clean, whitish looking.

Then disassemble again, run it through the UC, reassemble and lightly oil. You should be to the point where the chassis can run as well as it was designed, barring mfg. errors. Some just run better than others, no matter what.

Hope this helps. I do all this on my dyno so I can track the progress, but the same procedures will accomplish the same things, with or without the dyno.

Note: I think once you get the Simichrome you'll be surprised how much quicker it is to get the things broke in. I use a flat toothpick and just load the gearplate with it, and keep pushing it against the gears until it basicly turns dark gray.

This time, the gears you want to lap are the top three on the gearplate, and the bores the cluster gear shaft runs in. It's nice to have a way to adjust the speed of the motor, like an old Aurora wheel speed control, but a rubber band on a newer trigger type can work as well. Again, you want to get the Simichrome to "flow" around the gears and under the rear gear to polish the top bore. The bottom bore in the back is best done like the lower arm hole; with the chassis inverted. Let everything smooth out nicely, adding LL TC to "thin" the Simichrome. Reclean in the UC.

Install the rear axle and crown gear, and reassemble. This last time, you are going after the rear axle bores in the chassis, the spot where the crown gear rubs the frame, and the gear mesh of the crown and lower cluster gear. Make sure you get all these spots freed up, then disassemble everything and clean it all again in the UC.

Repeat the Brasso application at least one more time, it flows very nicely (it's a lot lighter grit than the Simichrome).