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Discussion Starter · #1 ·
I've not come across this problem before.

I have an RX42B motor which runs very, very slowly on start up. After a few minutes it starts to emit smoke for a while then bursts into life suddenly and runs perfectly normally.

It will then run quite happily for a long time with no further problems. If I leave it on the shelf for half an hour the whole process repeats itself. I have to go through the smoking start up phase every time I run it.

Any ideas for a cure?
 

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Oil on the brushes is my diagnosis, CMOTD. It burns off when the motor is run but seeps back when the motor is left a while.

Suggested cure: flood the entire motor with lighter fluid two or three times to wash away all oil traces, lubricate the commutator sparingly with comm drops if you have them and keep oil well away from the endbell during future maintenance.

Hope this helps,
L.
 

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Kitbasher
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I have a scaly car and a Pittman 196b that both do this, as they sort themselves out, and the are seriously quick I don't mind....
 

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I've got an RX42B that does this, I took it apart and cleaned it, cured it for a while, but it's gone back to how it was, it probably needs new brushes.
 

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Rich Dumas
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It does sound like oil on the brushes is causing the problem. Contact cleaner might work better than lighter fluid. I spray the brushes with the motor running at 6 volts. It is possible that oil has soaked into the brushes causing the problem to return. You could remove the brushes and heat them on the tip of a soldering iron to burn off the oil. If you can find replacement brushes it would be worth trying those.
 

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I have fixed these issues by taking the motor apart removing the disc capacitor on the comutator and resoldering the windings back to the commutator. The smoke comes from the bad connection at the commutator, the windings are just soldered and not crimped like they were in the good old days . But you are possibly making your motor illegal for some race series. Ken
 

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I've got a couple of SCX cars that have this problem - minus the smoke. Plus I had another 2 that got so severe one needed a replacement motor and the other I had a complete replacement car.

I'm begining to think that it would be a good idea for me to keep a replacement SCX motor in stock.

Slightly OT............ The only time I've had smoke is when the lights on SCX cars run-up the white flag. When that happens, the car slows almost to a stop for maybe 5 seconds, then there's the smoke and the lights go out, then the car's off again like a rocket!
3 of my SCX cars have done this now - Corvette, A110 and Sierra. Always the headlights, never the rears.
 

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This is a common problem when something has been put on the brushes and degrades the compound. Small pieces break off and become lodged between the com segments or a solvent/graphite slurry forms causing a short between poles; this is usually self cleared eventually by the current increase of the short "burning open" the weakest point in the short circuit; thus the smoke and fire rings around the comm.

I used to break in some of my RX motors in H2O or alcohol but I found that these motors tended to exhibit this problem more. I suspect that most any solvent may cause some problem with the scx brushes; this includes excess oil from the bearing. Many contact cleaners will also harm these brushes because they are formulated with a spec that only considers things like arcing caused by relay /switch contact bounce. The brush/comm interface can actually act similarly but many times a second. Some contact cleaners and solvents react differently in this environment and may actually damage the brushes. Most of the good cleaners are no longer produced because of the Freon component that was used in these solvents. The next best thing that is available, I guess, would be the high purity isopropol(rubbing) alcohol with one of the worst being common lighter fluid which degrades the SCX brushes quite quickly in my experience.

If you want to take the time you can take a set of 16D brushes and sand them down to size and use them. Some of those are made of pretty good stuff and can take more volatile compounds like lighter fluid.

I presently break in my RX motors using the passive method of driving the new motor with another through a crown gear transmission; this takes a little longer but seems to bed the brushes just as well without causing them to degrade.

Jimmy
 

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keep in mind SCX motors run poorly @ lower voltages, i've found 12v to be the lowest they can go. & keep oil away from the business end of the motor.
 

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Discussion Starter · #10 ·
Many thanks for your answers.

I went for the quick slosh with lighter fluid (as suggested by Lowrider) and it does seem to have cured the problem for the moment - time will tell if it lasts.

Incidentally, the motor has never been oiled but the tyres have been so it could be that some got onto the motor and caused the problem in the first place.
 

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Brian,

Are you running the SCX Nascars this Friday? Rumour has it that you might be but can't find anything on your calender..
 
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