8421 xl (2006)
After building the 8421 set, I decided to extend the set with the parts I already had. The crane is based on the original Liebherr 1160 (180t).
To make this extension available to other 8421 set owners I did draw the crane into the MLcad program... which took quite some time.
The specifications of the 'xl' version
* 4 wheel steering (3 front, 1 back)
* 2 wheel differentials, powered by a V12 engine
* 4 double pneumatic boom lifting mechanism
* boom extension powered by LEGO® chains, instead of original wires
* manual extension of the contra weight (battery pack) added
* side mirrors added at the driver cabin
The dimensions of the 8421 xl are:
* Length: 62 cm
* Width: 15 cm
* Boom height: 100 cm
* Boom length: 104 cm
* Number of parts: 2840 (original set: 1882)
* Weight: 3 kg
Boom extension by LEGO chains:
The original set uses wires to extend the 3rd boom. When extending the boom, it was clear that the original wires won't fit. Another complication was that wires will not be powerful enough to drive the extension of the 3rd boom. Therefore, I used the LEGO® chains to drive the extension. The chains are mounted on the 3rd and 1st boom by using the ''technic link thread', as can be seen on the picture.
Boom lift mechanism:
The original model uses 2 pneumatic cylinders to lift the boom. For the 8421xl model, this was replaced with a 'double' 2 pneumatic cylinder lift mechanism.
However, still one pneumatic pump can do the work.
Contra weight extension & Double
* Contra weight:
After finishing the 8421 xl model, it appears that the original contra weight was not really enough the keep the crane unit stable during operations.
This was solved by making the 'battery pack' (acting as contra weight) extendable.
* Double differentials:
By added more wheels to the 8421 xl I decided to apply the engine force to more then one 'wheel differential unit'. A second wheel differential unit was designed and connected to the first one. This was quite a precise exercise, because there was not that many space left for all the technic gears.
Side mirrors at driver cabin:
A small modification is made at the driver cabin, by mounting side mirrors. This makes the model more 'real looking'.
Another modification was made to the roof of the driver cabin. Due to the fact that chains are used for the 3rd boom extension, the boom rest upon the chains in 'driving position'. To overcome this, the boom support bars were modified.
The 8421 xl is made up of several sub models, because the model is to big to edit as a single ldr file. All the files are zipped with WINrar.
MLcad files zipped with WINrar
The following MLcad files are used:
Truck.mpd (Truck unit.ldr)
MLcad unofficial part list
Please navigate to the 'MLCad parts library' page on this website if you having trouble with the correct reflection of the *.mpd and/or *.ldr files within MLCad or LDview.
Probably you do miss some (or all) unofficial parts I did use within the model.
Upgrade 8421 to 8421 xl (additional part list)
People frequently asked me if there exists an additional part list inventory, needed to upgrade the 8421 to a 8421 xl. Well, here it is. Notice that MLcad parts do not always have the same number compared to the Peeron inventory (parts catalog). Example: Technic liftarm 1x2 is known under item 169 or 41677. Therefore, I do not claim that the Excel comparison is 100% correct.. but it is certainly above the 95%.
Building instructions in Adobe PDF.
Although I never made building instructions for the 8421 xl myself, a fellow AFOL 'LEGOlijntje' did generated the building instructions. These instructions can be downloaded in 2 parts. Please notice that I'm not the creator of these instructions, so I can not help you if problems occur.
MLcad building instructions:
The following information is useful to build the 8421 xl.
1) Technic models nowadays uses frequent 'mounting axes' which must be 'pushed' into a sub-model part which was build separate (see page 72 of the 8421 building instructions; i.e. mounting the outrigger). Within the MLcad files, these mounting axes are already in 'pushed' position. Keep this in mind when you want to mount individual sub models.
2) The installation of the 'crane mounting unit' will be easy and without enforcing the LEGO® parts when you slightly turn the outrigger mechanism into the 'out' position. As such, the crane mounting unit will drop smoothly over the technic knob wheels.
Version 3.0 of LDview will give the correct 3D views of the 8421 xl. Previous versions had problems with multiple ldr files loaded into one mpd file.
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