Repair of a Lego Duplo 2933 and a Duplo 2962 Train Engine

When our kids were little, they loved to play with their Lego Duplo train set for years.

That was some time ago, but today kids still love to play with these train sets, they are quite durable and they tend to last (almost) forever.

So, yesterday, my wife got a well-used combined amalgam of Lego Duplo 2933 and Lego Duplo 2962 Train Sets from a couple of children that had outgrown them. Since she acquired them for other children to play with, we immediately checked things for cleaning and possible repairs.

As it turned out, testing the original engines quickly showed that the years of play had worn them out so badly, that even with new batteries, they barely moved on the tracks. No good to play with much.

So, what can we do?

Well, take it apart, of course….

2 Small Flathead Screwdrivers

1 Universal Tool (Toothpick)

3 Guitar Tabs

2 Replacement gears (7,50 €/p) e.g. Ebay

Soap and Water, Alcohol

Grease

On the Internet, I didn’t find much on the engines at hand, so I figured, I would just try it myself.

It turns out, that looking on the underside, there is a roughly 2 mm thick and 2,9 cm long blue/green strip within the the yellow base at the front of the engines and two similar 7 mm wide strips at the rear end that hold the blue/green tops and yellow bases together. Additionally, here are two steps on each side of the engine that need to be pried aside when removing the base.

So, opening the engine is the most difficult part - as usual with Lego. They make things for clever kids, not stupid adults!

It’s s not that difficult though, if you know that the indentations on the blue/green latches are on the outsides each time. If you use a couple of small flathead screw drivers and a flat sheet of plastic (i.e. guitar picks), as well as some patience, it is easily possible to open the engine up.

The narrow latches are easily handled with two thin flathead screwdrivers - one to wedge into the yellow frame on the outside of the blue/green latch (remember the ridge) and one to lever/wiggle the top and chassis apart from the side of the engine.

When one is loose, put in a universal tool (toothpick) in to keep them apart and work on the other latch.

Next it makes sense to wedge in two flat bits of plastic on both sides of the train - ifixit tools are great here, i.e. the guitar tabs.

Finally the wide tab in the front is easily released if you push in a flathead screwdriver on the outside of the slot to open it up enough to push in another tab. Once this has cleared the ridge on the inside of the frame, it’s easy to pull the blue/green top and yellow bottom shells apart.

Once you have removed the base of the train, you can see the circuit board and the simply stuck on battery connectors. These can be easily pulled out of their sockets and cleaned, if there is some corrosion - as with the blue train engine.

The front wheels are simply hanging in their sockets.

At the rear, you have the motor and gear train. The former can be simply pulled out of its recess, after the gear assembly is removed.

The blue engine’s gear axles show some rust which is probably due to leaked batteries, but the motor works fine.

The printed circuit board is glued down with a small piece of double sided tape. It’s best to use two guitar picks to slowly lever it up.

Clean as much as you wish….

Both of the engines have the same problem - typical for these trains - that the white gear riding on the wheel axle has split and is loosely turning on the axle. When you insert batteries and turn the engine on, the motor and gear train run fine, but the wheels don’t turn, when you hold them, because the gear is ground out on the inside bore.

The solution, of course is to replace the broken gear.

7,50 € on eBay is not exactly cheap for a tiny piece of plastic, but better than buying a new train.

And yes, you could easily print them yourself - if you have the time for scanning and CAD and a printer….

To remove the broken gear, the wheel has to be pulled off the axle. Make sure that you pull the wheel straight out off the axle, because otherwise you may damage the wheel. That’s a bit tedious, but since they are simply pressed onto the axle, it’s possible - then the small grey frame and the gear are free.

Once (five days later) the replacements have arrived, they can be placed/pressed onto the axle, the small frame added - correct orientation (!) - and the axle pushed/pressed back into the red wheel. I used a vice for these type of compression maneuvers. The two new gears had an inner bore that was extremely tight, so I used jewler‘s files to widen them just a little bit.

Add grease/oil to all moving parts.

Maybe test again with batteries and then replace everything and push the two parts of the casing back together and you are done.

Both are running like new!

Time to test it with children once again….

It’s a really short Instructable, but I would have had an easier time, if I had seen one like it.

So I hope it’ll help you make your, or some other kids happy….

Stay fascinated!