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LEGO Technic 42009 Mobile Crane MK II Review


The Lego 42009: Is it worth the effort?

The Lego 42009, officially known as the Lego Mobile Crane MK II, is a giant yellow truck, touted by its official Website as ‘The ultimate lifting machine’. This design comes with exactly 2606 pieces. This particular build was released in 2013, and is a part of Lego’s Techic set – The biggest one of the series. We can actually imagine young children and preteens enjoying building/playing with this particular truck set, especially if they have a fascination with vehicles and construction. But of course, this build isn’t just limited to the younger set – If you like Lego or find this build beautiful, then by all means, go and buy your own box.


You can turn this massive pile of yellow blocks into something you can truly be proud of – A finely-detailed eight-wheeler vehicle. Like most of Lego’s builds, this truck is highly detailed, equipped with its own steering wheel that allows its drivers to rotate the truck’s structure. The best part here is probably the Lego Power Functions motor which also comes with the truck – This lets you lower the truck’s feet, extend its outriggers, and finally, raise the truck’s arm at least 77 centimeters in the air. What a feat! Just attach a hook to the truck’s winch, and be prepared to lift heavy loads. Simply put, if you are able to complete the Lego 42009, you have pretty much built the perfect lifting machine.


The complete build includes a comprehensive motor with its own moving pistons, ten wheels, and five axles. The truck is a 2-in-1 model that can construct itself into a container stacker. The Lego 42009 includes plenty of Power Functions, with raising booms and motor-powered extenders. These Power Functions can extend outriggers, raise or extend the crane arm, lower the truck’s feet, and retract the winch.


Accessories that come with the truck include an eight-wheel drive, ten wheels, a rotating superstructure, and finally, a highly-functional V8 motor with its own set of moving pistons. Other features include 8881 Lego Power Functions Battery Box, and an 88003 Lego Power Functions L-Motor. As mentioned, this truck has two wheels in one, and can also work as a truck and a container stacker. If you want additional stability, all you have to do is to extend the outriggers. The crane’s arm can be extended for up to at least thirty inches, right into the air. The truck is also so powerful, it has the ability to steer all eight of its wheels without exerting too much effort. You also don’t have to worry too much about your truck’s wheels getting jammed over something – And not only that, its engine pistons can move nicely as well!


So far, this has garnered plenty of positive reviews from satisfied collectors and builders from all over. They have praised how clear and concise the instructions were, especially since it can be quite a challenge building this truck from the get-go. In fact, the instruction booklet also teaches you how to dismantle the truck, in case you have to do it. The instructions on the official Lego site correspond very well to features on the actual truck. This just proves that building the Lego 42009 doesn’t have to be boring – Much like most of Lego’s major builds, the journey to completion can be just as exciting.


Of course, the Lego 42009 cannot please everyone – People have complained about its non-functioning headlights, and the lack of studs on its seats, which can properly hold your Lego minifigures into place. A lot of clients have also suggesting building a remote control specifically for this truck, to assist it in steering and rolling.


Like most of its boxes, the Lego 42009 comes in a huge matte cardboard box. Since this isn’t a tie-up to a popular movie, TV, or book franchise, the only thing you will see on top is the Lego logo, the word Technic, the truck’s official model number, and the recommended ages. The box itself is quite massive and heavy, which immediately tells you that this isn’t just your ordinary type of Lego build. The front of the box includes a picture of the assembled truck, with its lowered crane. A tinier picture of the same truck can be found on the upper, this time, with its crane outstretched. On the bottom right of the box, there’s a sign that tells you that this truck comes with two functions, and details one of these two functions can be found on the rightmost side of the box.


The back side of the box also includes the truck – Except this time, it’s split right in the middle. The purpose of this is to show you, once again, that the truck has two major functions on one model, namely: A container slacker, and the truck itself. On the left side of the box, you’ll find instructions on how to convert the truck into a container slacker, as well as the slacker’s functions.

The box is opened sideways. But before you can get to the actual pieces though, you will be greeted with the model’s front flap that has another gigantic picture of the Lego 42009, again with its crane fully extended. It showcases the different parts of the truck, such as the wheels, the base, the crane (and how long it can be extended and how many degrees), as well as the various wheels, functions, gears, axles and what not. One look is all it takes to see that this truck is a thing of beauty. On top, you will be able to see the accessories that come with it, including the battery box.


Open up the front flap and you finally arrive at the materials themselves. You shouldn’t feel too surprised (or overwhelmed) by the amount of mint packs found inside this giant box. The box itself is practically bursting at the seams with the amount of blocks squeezed in.



The Lego 42009 comes with twenty four mint bags, and in certain cases, smaller bags are placed inside larger ones. There are ten standard technic tires (which is a given since this is a Lego Technic build) after all, three strings with attached studs, two pieces of 32L axles, and a thick main string, an L-motor, the PF battery box (once again, a staple in Lego Technic builds), a sticker sheet, and finally – Get this – Six instructional booklets. Six!


In total, the Lego 42009’s build is divided into many segments. The first three segments involve constructing the carrier of the truck. Segments four and five deal with building its superstructure, and finally, the sixth one involves creating the boom. As usual, the mint packs come with their own respective set of numbers. However, a good portion of the blocks used for the build belong to the very first segment.


But as grand as this build might seem, there aren’t any new parts featured in the Lego 42009. The only new parts here are as follows: Eight gears which you can slide right into the axles. These are mostly used in the truck’s outriggers. There are also four new panels, which can help you a lot when you’re in the process of building your truck – Since they can be used to perform plenty of brand new functions. The 8T gears that come with the truck are technically new as well – But only in size, since they’re slightly bigger than the usual.


Mint pack number one already has plenty of blocks stuffed inside it – At least one thousand pins in total. Also included are a dozen gears and beams, twelve gear racks, four mini-LAs, frames, and three yellow square panels.


The carrier is the first thing to construct in this behemoth of a vehicle. While building this particular part, you might notice that the steering is quite different as compared to the Lego 8421, another model involving a truck. Its gear ratios are also different from the truck’s axle. But for the Lego 42009, everything is the same and you can complete various kinds of ratios even if you use different types of racks. The two inner axles in this mint pack contain a 4L offset for a steering angle, measuring 13 degrees. There’s also a rear axle 3L offset, as well as a maximum angle of 17 degrees, an angle measuring 21 degrees, and a front axle with a 2L offset. The 32 axle helps you in turning the wheels of your truck. The middle axle is not used for steering, but it has a driver eight-cylinder fake motor.


The truck has a rather long body – While constructing it, you might even imagine what the final outcome would look like. The five axles each have different types of turning angles, and they have to work together to get this truck to work. The truck is packed with eight-tooth gears, which all utilize a brand new design that Lego recently introduced to the public. The gear was most likely made to prevent it from sliding right into the beams’ holes, and to stop the teeth from slipping out. And not only that, they seem to be a bit sharper as well.


The second mint pack contains the stuff needed for the truck’s superstructure. There are forty gears in this pack, and this time, the build here becomes slightly tougher as compared to the first one. Pay close attention to the instructions found on the booklet, since one slight misstep can make this part of the truck look different. However, this part is still fun to build. Included in the gears are two normal LA-s, and one more square panel. After you complete this segment, your truck must be covered with panels.


Another part that requires your utmost attention while being built are the truck’s cabins. This area is very compact, and contains the heart of the vehicle – The motor that is used to perform its functions. It’s also a bit challenging to spool the string – According to the instructions, you should thread it around the truck’s pulleys. But the thing is, the axle doesn’t turn around as easily, since it creates friction against the other axles, no matter if you have tied a knot or not. If this part frustrates you, then just tie it around the axle. Although this part also has its consequences – If the truck tries to lift up a huge load, the string just slips around the axle while turning. So make sure to wind the string on the correct axle.


Next are the parts for the third segment – Containing six curved panels. Compared to the other panels found on previous models, the ones with the Lego 42009 contain twice the number of mounting holes. This allows you to create excellent, self-sustaining construction with the truck itself – And this can certainly help you in the last stages of the build. The other panels can only be used to cover something up – These are used for constructions.


Meanwhile, the crane, which is pretty much the main centerpiece of the truck, is a giant piece – Just as big, if not bigger, as the one found in the Lego 8421. The crane’s separate parts are well-paneled. You can pile up the beams together to create a flat, solid surface, and this is pretty much the reason why there’s a huge amount of beams in this particular segment.


Also, if one takes a good look at the back end of the truck, the battery box is sticking out – This is one of the handful of downsides that came with this truck. Behind the truck’s cabin, you will find at least eight-cylinder motors. This allows you to look at the truck’s piston movements, since they’re not covered with a panel.


The Lego 42009 contains loads of functions. The truck’s L-motor has to be placed inside the superstructure. With this, it can send power to:

  • Pulling the truck’s main wire using the hook. This is contrast to the one that the Lego 8421 has, which cannot be synced while the boom is being extended. The 42009’s hook isn’t made from metal, which is a huge downside.
  • The outriggers. The power passes through the truck’s turntables, then to the main carrier which contains the truck’s extra gearbox. This lets you switch the truck’s functions from between pulling stuff in or out, and lifting or lowering load.
  • The truck can now carry the main beam across two synced LAs.
  • It can now extend the boom, right through the system of studded strings, and across gear racks, allowing it to be stretched in both segments simultaneously.

These main functions actually work nicely, with the exception of the second one. These functions are all protected using white clutch gears – So even the youngest children can play this without risking choking hazards. The steering wheel also works nicely, however, the wheel is slightly bigger as compared to the 8421.


The five axles required for this truck to function all have various types of turning angles, so you can freely drive this truck to your liking. Another way to achieve this is through varying the distance from the wheel and axle, to the truck’s own gear rack. The third axle in the truck doesn’t even turn, and instead, assists the other axles in pivoting. The third axle is also important since it has a differential gear that can help the outer wheel turn much faster, as compared to the inner wheel. Other axles can do this, but the impact isn’t as great as the third one. One or more of these types of axles can change the way the truck moves.

However, certain people have had trouble with the axle 16, since it must be threaded right through the truck’s smaller actuators. You must also place in one of the truck’s 12-tooth bevel gear, as you do this.


The panels found above the truck actually give it a more detailed touch. These aren’t locked into place as compared to the other parts that come with it, so you can lift them up easily in case you want to check out the gear trains beneath it. This can be helpful if you want to debug the truck.


Pros: A lot of people who have purchased this model have enjoyed the usage of the L-Motor. And despite being labeled as a model suited for pre-teens and teenagers, the Lego 42009 is perfectly suitable for practically every age. Cons: There have been plenty of suggestions to add in a remote control to this truck so it can operate smoothly. The crane can only take so much weight – So don’t put too much heavy load on it, or else it will snap. Nobody wants a broken crane! And finally, this model is a bit pricey so you might want to save up if you want to buy.


All in all, it will take you at least nine long hours before you can complete the truck’s body, let alone the entire vehicle itself. When you compare it to the 8258, this one has a bulkier size. But as they always say – To each their own. Despite all of its shortcomings, the Lego 42009 is still an excellent build.

Product Overview: Lego 42009 – Lego Mobile Crane MK II

Product Dimensions: When crane arm is retracted – At least 8” (21 cm) high, 23” (59 cm) long, and 5” (15 cm) wide. Container stacker measurements – 20” (52 cm) high with its boom completely extended, 19” (50 cm) long, and 7” (18 cm) wide. Container truck measurements – Around 3” (10 cm) high, 11” (28 cm) long, and 3” (8 cm) wide.

Item Model Number: 42009

Manufacturer Recommended Age: 11-16 years old.

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