I've ordered 2 Kazi trains on aliexpress. Seemed like a nice set with some tracks for my kids. As seen below it's a set where the power box is a separate part and it runs a motor that connects to the wheels by a bunch of gears. Problem I have is that the trains are struggling to run. Yellow one more than green, maybe due to weight. Anyone had a similar problem and knows how to improve the set? I'm wondering if switching to the undercarriage motor would work on these sets. The larger ones seem to have a different kind of motor that has no gears to get it moving and provides power directly to the wheels but not sure if that one would fit. Considered applying some grease but not sure how much that can help in this case without making everything sticky.

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2 Answers 2


So I have done some more investigation into the problem on my side and there are several ways to go into this. First thing I did is I switched the battery brand from regular Maxell to GP extra which improved the condition but I still could not fully use the battery box in terms of speed regulation but an improvement none the less. Then I tried a couple of combinations:

  1. changed the rubber on the wheels - no significant improvement all though the rubber I got originally is a lot worse in terms of quality
  2. I used a combination of the original battery box and the undercarriage motor - best solution if it fits your train - you need some additional bricks to do the change probably - speed settings work well also
  3. New motor and a 6 AAA battery power box - works well but no way of changing the speed with this power box - does not improve with the 5 battery box

So essentially the problem is in the gears which get stuck a lot, make a lot of noise and have a lot of wear - a lot of dust everywhere.

In case you're considering buying a train that is using the M motor like mine the best solution is to switch to undercarriage. Some trains are bigger and use the undercarriage by default so those will probably work better although the overall train weight is higher.


Stronger motor

Wheels with rubber

Power box 6 batteries


First thing is what batteries are you using with it ?

Some devices do not run well on rechargeable NiMh or NiCad batteries as their voltage is lower initially. So you may see lights that are more dim, motors run slower or so on.

Many devices may have voltage regulators or DC-DC converters where this not an issue. Simpler childrens toys and so on are often wired directly with no power circuit and are not optimal for rechargeable batteries.

You can also have some issues with heavy duty batteries not working correctly (not just shorter life), so if not already done troubleshoot with a set of fresh decent quality alkalines and go from there.

If that is already the case we can move on to looking at other possibilities.

  • Hi, thanks for replying. I'm using regular AAA batteries. Was considering the rechargeable but since voltage is lower than with the regular ones I'm guessing it's not gonna work. I saw some ideas of making your own battery pack but question is also weather you can put a bit more power in and not damage the motor.
    – Debely
    Jan 2, 2023 at 10:49
  • deafeningly the Offical rechargeables are 7.4v output
    – LKBricks
    Jan 4, 2023 at 4:22

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