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I have always really liked the way lego steam engine 3741 looks like, except that the 9V motor makes it look less good. The sound of the 9V motor fits very well with high-speed trains, but does not fit with a steamer. But the bigger problem is that 9V has no moving pistons. Both of these problems are solved by replacing the 9V motor by a 12V motor. The 12V motors have moving pistons. All of the non-standard pieces that you need to turn 3741 into a real steam engine are included in lego set 7865, which contains the 12V motor, the moving pistons, the corresponding cylinders, and a few other pieces. The cylinders do not fit underneath the train base plate (at least, if you want to be able to take curves). But it works if you extend the 3741 train by 4 studs (longer looks better anyway) with a 4x6 black plate. Placing tiles on top of the cylinders from lego 7865 allows the cylinders to slide underneath the 4x6 plate, and the rest of the motor (the cylinders are attached to the 12V motor) can rotate underneath the train base plate as usual.
Here is how the 12V version of the 3741 train looks like:
As you can see, the boiler also had to be made longer, but that looks better anyway.
Here is another picture
(I had some difficulties making pictures, the flash light of the camera messed up the colors in this picture) and here is the 12V motor with pistons and cylinders attached:
I use this engine to pull three logging cars (from the My Own Train series), two MOC wooden-looking cars and a caboose. Adds up to about 5 feet plus a few inches long, but these logging cars don't weigh much so it's an easy load for the motor. This 12V 3741 train is definitely cheaper than my Emerald Night with power functions, but I like it at least as much, if not more (the 12V motor with its pistons sounds much nicer than the high pitch XL motor).
