Read the review below or jump straight to the photos and videos! LEGO Technic 42009 Mobile Crane MKII

I was lucky enough to receive a pre-release copy of the LEGO 42009 Mobile Crane MKII Technic set, thanks to Kim from the LEGO Community Engagement & Events team. This is my first proper set review so hopefully I will get better with each one, as well as get the hang of the camera setup I've just started using! I was naturally quite excited to receive this set, especially considering it takes about 300 years for anything to get delivered to Australia, and the anticipation was killing me!

Edit: This set now appears to be available for sale in some countries. Try Amazon or eBay.

This is the largest technic set ever produced in terms of part count - 2606 to be precise. The next biggest being the 8110 Unimog U400 with 2041 parts, this is quite a difference. Although with over 1000 pins, some might call that cheating! There were definitely times when it seemed that the use of so many pins was a bit overboard, but I guess they provide additional strength - for example in the boom arm where it's important to be as strong as possible. This set also has 162 gears, 290 axles, 591 beams. See the inventory page for the full breakdown.

How similar is this Crane to previous Technic Crane sets?


Rebrickable users can see how many parts of this set they are missing from their collection by clicking this Build link.


This set has also been reviewed by Techlug (French) and TechnicBricks.

Box Contents

The box is quite heavy as is to be expected, sorry I don't have accurate scales to weigh it.

The back of the box has a couple of perforated sections which you can tear to open it a bit easier than the old way of ripping the backing off. It's an improvement, but I would like to see a method that limits the destruction of the box a bit better.

Inside are:

  • Cardboard backed packet of instruction booklets/stickers/string
  • 24 plastic bags of parts
  • 2 x Axle 32 (used in book 2, one is spare)
  • 3 x 31L String (used in book 6, one is spare)
  • 1 x 9V Battery Box (used in book 5)
  • 1 x Large Motor (used in book 4)
  • 10 x Tyres (used in book 3)


LEGO Technic 42009 Box Contents

The bags are numbered which is a first for me with large technic sets. I'm used to seeing the numbers only on the smaller sets I own buy for the kids. There are 15 bags with #1, 5 bags with #2, and 4 bags with #3. A quick look at the instructions revealed why. The build is broken up into three main parts:

  • The main truck body which uses the 15 x #1 bags and books 1 to 3.
  • The cabin which uses the 5 x #2 bags and books 4 to 5.
  • The boom arm which uses the 4 x #3 bags and book 6.


Yes that's six books! The image on the front of each instruction book also shows the section that it's building which I thought is a nice change. The first page of book #1 has a new cartoon describing how to sort out the parts. Not sure if this is an improvement to the old one but I guess it's more LEGO'ish?

  • Book 1 has 83 pages
  • Book 2 has 75 pages
  • Book 3 has 83 pages
  • Book 4 has 67 pages
  • Book 5 has 34 pages
  • Book 6 has 83 pages


LEGO Technic 42009 Instruction Manuals

So as expected, the truck body comprising the first three books makes up more than half of the build effort.

The stickers are also now numbered which will help avoid mistakes.

The first thing I actually noticed after tipping out the box contents were the two Axle 32s. I don't have any other sets with these in them, and they seem quite fragile. I can't help but wonder how long until they break, and what possible need could there be for them that multiple smaller axles couldn't achieve. It's interesting that one of them is a spare, so perhaps TLG anticipate them breaking? I guess some AFOLs wouldn't have a problem, but I think that inexperienced builders could easily break this. There are also 5 x Axle 16s which are also a bit fragile in my mind, and actually mine ended up slightly bent while trying to insert them as you will see below.

There are a couple of new part designs, and some parts in new colors:

  • The red 8-tooth gear has a different internal cross section to allow it to easily slide along axles. These are used to allow the horizontal stabiliser arms to extend while maintaining a gear train with the vertical stabilisers.
  • The Curved 11 x 3 Panel has a new design with more pin holes.
  • 63869 Connector in black
  • 50451 Axle 16 in black


LEGO 42009 - New 8 tooth gear
LEGO 42009 - New 11x3 Curved Panel
LEGO 42009 - New 11x3 Curved Panel

Also, all of the 8-tooth gears are using the new design introduced this year (2013). This design seems intended to help stop the gear from sliding into the holes in beams, and is perhaps a little stronger to help prevent teeth slipping. They also seem considerably sharper as my fingers can attest to!

Build - Truck Body

Opening all the plastic bags and sorting them into relevant containers is almost as much fun for me as the actual building :) There are also several bags with the smaller parts such as pins within the larger bags.

This truck body is long! When building I would often think the length was finalised, but then another bit would get added on. The 5 axles all have different turning angles, to allow a truck of this size to be drivable. This is achieved by varying the distance between the gear rack and the wheel axle. The third axle does not turn at all and is the mid-point around which the other axles pivot. It is also the only axle with a differential gear to allow for this as the outer wheel needs to travel a lot further when turning than the inner wheel does. This is also true of the other axles but not to as great an extent which I guess is why the designer decided not to put differentials on all of them. The added complexity to do this would have also been quite a challenge!

The main part I had trouble with as mentioned above was with the Axle 16s. They needed to be threaded through the small linear actuators and insert a tan 12-tooth bevel gear while doing so. I found these quite hard to put on in the best of times, so doing it while threading a long fragile axle was even harder.

LEGO 42009 Bent Axle 16

The panels that sit on top of the truck body are a nice touch. They are purposefully not locked into place as securely as other parts so that they can be lifted up for inspecting the gear trains underneath. Very useful for debugging problems as I would discover later on!

It comes with the standard V8 engine design which to be honest is getting boring. It's the same basic design that's been in every Technic set for quite a while now (20 years?). Yes it looks good, but something new and refreshing without requiring new part designs would be a welcome addition. The instructions had this one being built upside down, but you can't fool me, it's still the same :)

It took me about 9 hrs of building to complete the main truck body. This was a relaxed building schedule with time out for eating, photos, etc.

The completed truck without the cabin/crane attachments doesn't look very pretty to me, compared to say the 8258 body.

Build - Cabin

This is definitely the most complicated section as it is quite compact and houses the single motor that needs to drive all the functions. This complexity means that for most of the time, I was pretty clueless about the purpose of all the little sections that get built and then applied to the main section. As it was slowly built up, things became clearer and I could start to guess at what was coming next.

I would love to see some rendered images of just the gear trains included in the instructions. I find that stuff very interesting and it would also help with diagnosing problems or modding the set for improvements.

It felt similar to the 8043 build, in large part because of the double linear actuator setup.

I found it hard to spool the string. The instructions indicate to thread it through the pulley wheels, but then the axle does not turn easily as it rubs against the neighbouring axle's gear (with or without a knot in it). The easiest way I found was to tie it around the axle instead. However, this means that when it is lifting a heavy load, the string will simply slip around the axle while it's turning. If I had of managed to tie it through the pulley though, I feel that the 24-tooth gear with clutch would have slipped instead. Also be sure you are winding the string onto the axle in the right direction as I got that bit wrong. Twice :)

Mounting the cabin on top of the truck body caused me some problems. The instructions at the end of book 5 tell you to test the power function connectivity after mounting the cabin. Unfortunately I got the Crunch of Death(tm) sound that means I screwed up somewhere. Mounting the cabin onto the truck wasn't hard, but getting it off was another matter entirely. There are four pins that are used to secure it in place and they don't come out very easy, especially when they are hard to get at - I could not get my fingers either side of them to pull. I am ashamed to say I resorted to my needle-nosed pliers to extract them, luckily no visible damage was done.

LEGO Technic 42009 Mobile Crane MKII

Here are the steps I went through to resolve the problem:

  1. Turning on the motor again with the cabin detached I could see it was working fine, so the problem must be in the truck body.
  2. I opened the handy flaps on top of the truck to view the gear trains and was able to move the horizontal stabilisers quite freely.
  3. I placed the cabin back on and tried again and the horizontal stabilisers worked fine this time. I guess there was just a bad connection when I mounted it. However, the vertical stabilisers would not work now.
  4. I put the clutch gear in neutral and turned the gears manually. The drive shaft connecting to the cabin's motor moved easily. The shaft connecting to the stabilisers would not move though. I could move them with enough force but there was a lot of friction somewhere.
  5. Visually inspecting all the gears showed that none of them were wedged in too tight, they all had a bit of give in them.
  6. I then disengaged all four linear actuators to see what difference that made and the gears could turn quite freely after that. Re-mounting the cabin and testing confirmed that it works fine in that state (other than the stabilisers not moving of course!).
  7. I put them back on one by one to test the motor. You can see quite a bit of wobble due to the bent Axle 16s.
  8. Of course once all four were back on it worked perfectly! I'm guessing the tan 12-tooth gears were not in properly the first time.


Despite this problem, I definitely enjoyed building this section. Solving these kinds of problems is half the fun of building a large complex model like this, and forces you to better understand how everything works! It perhaps would be nice to have more points during the instructions that test these things though. There are some, but apparently not enough for me :)

It took me about 3 hrs to build this section, including fixing the stabiliser issues.

Build - Boom Arm

The mechanics of the 3-part boom are quite interesting. I've never built something like this before, so went into it with no idea of how it might be achieved. The two strings with end studs confused me for quite a while, and once I became clear of their purpose I was suitably impressed.

When all three parts to the boom were inserted together I got carried away and was looking at how long it could get. Unfortunately, some of that length is lost in order to maintain strength of the overall arm when it is extended.

This section was the quickest to build at around 1.5 hrs.

LEGO Technic 42009 Mobile Crane MKII Boom Arm

Build - Overall

There were several places in the build where parts were connected only temporarily and then removed later on. This usually confused me and made me wonder how it was going to work like that. When they are removed, the light bulbs go on and I am left appreciating the cleverness of the solution.

I think the boom arm was my favourite section to build even though it was the simplest and quickest. Probably because it was the most unique design for me. The cabin section was also fun to build and anyone looking for complexity will find it here, although I think the 8043 gearbox was probably a bit more challenging.

One mistake I kept making over and over again, and it's not limited to just this set, is the confusion between Dark Bluish Gray and Black beams. When the two colours are not next to each other on the page, I find it very hard to know which one it's supposed to be. I have to skip ahead to see it in context to figure it out. I'm not sure if that's just an issue with my vision or affects others too. There were several times when I ran out of one colour but had the other colour left over and realised I'd screwed up.

Maybe it's just my girly hands, but putting this set together hurt. For days. My finger tips were quite red and sore afterwards. I particularly disliked the new 8-tooth design as it seems much sharper and evil than the previous one, although that might just be my imagination.

I built this set over two days, as sadly I have a day job :) It took a total of around 13-14 hrs. I'm sure a lot of you can build it faster, but then it would be over faster too. In my defense I also had to take lots of photos and had "help" from my kids.

LEGO Technic 42009 Mobile Crane MKII


This set has lots of nice features that are easy to miss. All of the doors can be opened - the two on the main truck body as well as for the operator of the boom arm in the top cabin. Also, the steering wheel can easily be fixed and moved to the correct right hand side of the truck :)

The motor drives five different functions:

  1. The horizontal stabilisers
  2. The vertical stabilisers
  3. Lifting the boom arm
  4. Extending the boom arm (the two internal parts move at the same time)
  5. Lowering and raising the hook


LEGO Technic 42009 Mobile Crane MKII Power Functions

I would have loved to see the stabilisers connected somehow so that the vertical ones started dropping automatically once the horizontal arms had completely extended. I have no idea how this could be achieved, but those designers are clever people :) I also think they move far too slowly, especially the vertical stabilisers. You have to watch them for several seconds just to be sure it's moving in the direction you wanted. Unfortunately, they are not strong enough to lift the weight of the truck. Fully dropping the vertical stabilisers will see them grind to a halt eventually, if you lift the truck up they will continue for a tiny bit more. However if you try to push the truck with them fully deployed, you will see that they do have some grip and will start to bend sideways.

The steering works well via the Hand Of God wheel, located at the back. The varying wheel angles and differential make it very smooth and easy to turn. Plus, the turning radius isn't bad for a vehicle of this size.

The boom arm is quite nice. The whole top can also swivel around 360 degrees while the motor is on. Extending the arm goes quite smoothly, but when it's retracting there can be some judder sometimes, i.e. it stops moving for a second then suddenly and quickly makes up the distance. I'm not sure what is causing that, perhaps I didn't do something quite right in the build.

The string is 2.5m long, so there is plenty of room for play. For example, with the truck on the table, I can lift something off the floor.

I was very curious as to how much weight it could lift. The first thing that came to mind was my 8070 Supercar, plus it happened to be the only LEGO set I had assembled. I know it's a bit much to ask, I believe it weighs somewhere between 1kg and 2kg although I don't have accurate enough scales to know for sure. I eventually settled on something a bit lighter as you can see in the video. I will do some more testing later after I've built a few more sets to test with :)

Some updates:

  • 42008 Service Truck = Fail
  • 42005 Monster Truck = Fail




The B-Model for this set is the Container Stacker & Truck. The instructions for this model must be downloaded from the LEGO Technic site, but they are not yet available. When they are, I plan on building it and will update this section with some details!

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Related LEGO Technic Reviews:


  • 1 year, 7 months ago DJLF Level 8 MOC Designer
    I didn't get a spare 32 in mine
  • 6 years, 3 months ago TobyMac Level 33 Inventory Admin ADMIN
    Just finished the B-Model. It's very nice, specialy for a B-Model.
    Nice to see that the 32-axle is actually needed in this model, as it wasn't really needed in the main model
  • 6 years, 7 months ago Bricks4Evr Level 8
    Hi. Great site. Great review! I just finished this set myself. The issue of "jerky motion" when retracting the boom is due to the worm gear ,(located on top of the boom), that drives the extension/retraction function. It can slip forward / backward a bit on it's axel. When retracting, the worm gear moves reaward as far as it can, then begins to turn the gears that move the rack gears. But then gravity causes the boom section to slip down, forcing the worm gear forward. A delay occurs while the worm gear moves rearward again. I solved this by making a thin shim from plastic sheet ,(the type some products are packaged in). Install the shim infront of or behind the worm gear. Thanks again for such a usefull site.
  • 6 years, 8 months ago Chassie Level 5
    Just purchased this model, because in a matter of months when these sets are no longer produced, you will find greedy idiots charging £300-400 on amazon and ebay for this particular model... So I'm waiting in anticipation now.....So excited!!! and I'm 39 .... brings me back to my first set in 1979.. a really small version of this maybe a quarter the size...but was my first set ever. Happy childhood memories
    • 6 years, 9 months ago Nathan Level 28 Site Admin ADMIN
      It's a very heavy set, would be interesting to see how well it can be driven.
      • 6 years, 8 months ago mbaudais Level 2
        Just finished building this set - 12 hrs total and enjoyed every minute! I concur that this was hard on the fingers...

        Rudolpho's comment is along the lines of what I was thinking. Between the front seats of the cab there appears to be enough room for a servo motor (connected to the steering axle) and a large motor (connected to the drive axle, although it would need reduction gearing I think). It almost appears as if the set was designed with this in mind...

        I find the rolling resistance to be very low. I'd expect a geared-down drive motor to work just fine. You wouldn't want it to go fast anyway since that would be completely at odds with the speed of all the other functions... :-)
  • 6 years, 9 months ago shany Level 3
    can someone please add a link where I can buy this crane? from some reason, I couldn't find by my self.. thanx
    • 6 years, 9 months ago theskirrid Level 30 MOC Designer ADMIN
      Should be available from July-August depending on your country, this was a pre-release set... I can't wait either :-)
      • 6 years, 9 months ago shany Level 3
        wow, such a quick answer! it's nice to know we r not waiting alone :-)
  • 6 years, 9 months ago alwin Level 5
    thanks 4 the review. i pre-ordered mine a few weeks ago. still have 2 wait 4 it 4 a few weeks, sadly. i do not agree with the comment that a large scale lego set will not sell... i have the big scale millenium falcon for excample, which costed eur550, excluding mail taxes, eur35, delevered 2 me in the netherlands,straight from the factory in danmark. i do not think that was a lot of money 4 something i really wanted, and i knew it was coming for almost a year before release... google around these days and one will see the same set, when complete, will do eur1200 or more... mine is not 4 sale by the way. did anyone notice that usually the lego boxes contain a lot of air? the mf did not: it was comletely stacked, weighing a lot, duh, almost 5200 peices, but compact: only slightly bigger (higher) than the unimog. i would like 2 see more bigger and detailed sets from the company any day, the sooner the better. google around and you will see a lot of great stuff being build. try rebrickable.com for start...
  • 6 years, 9 months ago h.ymin Level 3
    Great review!Full of humor and I must admit that I also have misrecognize the gray and black beam all the time as you did:-)Greeting from China!Forgive my poor English grammer- -And after this review,I'd say I want this set badly!Now I'm restoring health(a chinese statement in "saving money"),because it's a big fortune for most of Chinese```
  • 6 years, 9 months ago teaandbiscuits Level 4
    This is a great looking model, and despite only recently buying the 8053 mobile crane I'll probably get this too.

    I would love to see some even larger models though. I know the price and marketability is a huge factor for Lego, but I would love to see more models at the same scale as the Unimog. A crane at that scale would be a monster! Yes please.
    • 6 years, 9 months ago theskirrid Level 30 MOC Designer ADMIN
      Agreed, a monster set would be great but:- <br>
      1. It would cost a fortune, and not sell in large amounts<br>
      2. Would have a box the size of a Dacia Sandero™<br>
      3. Would weigh more than me [quite a bit]<br>
      But I still want a set on the scale of Sariel's missile carrying truck. :-)
  • 6 years, 9 months ago msx Level 19 MOC Designer
    very accurate review, thanks :) i can safely say that i want this set badly.. i hope some day i'll be able to get it
  • 6 years, 9 months ago FilipeR Level 3
    You seem to have little exprience with technic flagship sets.
    Other than that, great review! Lots of details and useful info.
    • 6 years, 9 months ago Nathan Level 28 Site Admin ADMIN
      I admit I don't (8258, 8043, 8070 are the largest I have). I'm just wondering what makes you say that though? Is there a rookie mistake I'm making :)
      • 6 years, 9 months ago FilipeR Level 3
        No, you simply failed to build this set. You bent an axle 16, the "Crunch of Death".

        But overall, it was a great review! :)
  • 6 years, 9 months ago MG1 Level 5
    'nobody tosses a dwarf'... :)

    Can't wait for this set...it looks awesome!
  • 6 years, 9 months ago Bachaddict Level 15 MOC Designer
    Looks like 8421 still beats it on turning circle and proportional arm extension!
  • 6 years, 9 months ago Pjefferson Level 10
    Great review Nathan. Full of interesting facts and humour (I have experienced similar problems in the past).

    Only problem is now I want one really badly!
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