8851 Excavator Review and Pneumatic Upgrade Guide

I was into Technic mostly during the early to mid 90s and I was a fan of pneumatics, which got me the 8868 Air Tech Claw Rig eventually , but quite a few pneumatic sets and parts before that. In that time, when looking through an old catalog from the 80s, I saw a different pneumatic system. While I didn’t understand the difference, I knew it was an older generation and I was intrigued by it. I got lucky and grabbed probably one of the very last 8851 Excavator sets from the local toy store a bit later (could have been 1994, ten years after its initial release!). I was happy to get such an old model in a new box and for a good price (I could afford it from my pocket money, if I remember correctly), and I could finally get my hands on that old pneumatic system.

Needless to say I saw the difference when building the model and I understood the drawbacks the old system had (from a construction point of view), but the excavator itself was so cool for some reason, with its tracks – it’s still the only set I have tracks from – and rugged look, even though the design is clearly 80s-style Technic with a lot of detail missing, and very blocky. But the thing performs like a real machine which makes it all the more interesting considering its relatively small size. It also looks more realistic than the 8837 Pneumatic Excavator that came after it. Because of that, I always kept this old Technic set close to my heart.

I have only recently returned to Lego and I’m rebuilding my favorite models, so I knew I had to get that excavator built again the moment I found the old pneumatic parts and the tracks in my collection. But there was one problem: I have all the actuators and the distribution block, but the red pump is missing. Since you can’t use the new pneumatic pump with the old actuators and I didn’t want to order more old pneumatic parts just for this one model, I thought, why not upgrade the pneumatics and get rid of the flaws of the old system? But it would not be so easy with twice the number of hoses to be laid through the model’s bricks, and anyone who has built the 8851 set knows how finicky it is to get the original hoses placed…

So it took me quite some time to get it right and involved some deconstruction and correction of mistakes I made with the new pneumatics, especially considering hose length and placement. When taking the model apart, I took lots of photos to document the process in reverse and inventoried all parts needed. Now *you* can build your own pneumatic upgrade for your 8851 Excavator if you follow this building guide. I hope you enjoy it – and do post comments and photos if you find something that could be improved!

Required parts

Before you begin constructing your excavator, look at this picture and the following list to find out if you have all the required parts for the upgrade. All the pneumatic parts are listed except for the valve switches since these are already included in the set. You will not need the distribution block or any of the old actuators and pump. The other parts are for attaching things related to the upgrade. Note that colors can be varied by you and have only been picked by me because I find them fitting or I didn’t have parts in other colors (the black clamp plates, for example, could be gray). I used old (from the original 8851 set) and newer pneumatic hoses because I did not want to cut anything, so the model looks a little mixed up on the photos. Keep in mind the old hoses are more rigid and less flexible than the newer ones, which is why I used clear hoses for the switches; they seem to be the most flexible. Your mileage may vary.

pneumatics:

1x pneumatic hand pump with brick-shaped bottom (1990s)

3x large pneumatic actuators with brick-shaped or round bottom (1990s onward)

2x t-piece (original 8851 set has four, but we only need two)

2x rigid tube (Flex System), 4 cm (used on sets such as 8868 and 8837)

1x hose, 2.5 cm, clear

1x hose, 4 cm, clear

3x hose, 4 cm, gray

hoses 5.5 cm, 16 cm, 18 cm, 19 cm, 21 cm, 24 cm, 28 cm, 39 cm, black

other parts:

1x Technic brick 1x8 with holes, red

1x Technic brick 1x2 with hole, old gray

1x brick 2x4, black (optional)

1x Technic axle 10

2x Technic bushing, half-width

4x plate 1x1 with clamp on top, black (or old gray)

4x Technic pin, half-length with stud

Construction guide

Alright, let’s get started! Open the 8851 building instructions (available here), gather the parts needed for the model, and follow the steps like this…

steps 1-3:

Build as instructed.

step 4:

Ignore the instructed attachment of hoses. Do this instead:

attach gray 4 cm hose to center lug of switch

attach black 19 cm hose to left (bottom) lug of switch

attach black 21 cm hose to right (top) lug of switch

step 5:

Lead the gray hose through the third hole from the right side of the brick (where the left of the two hoses in the instructions is placed). Attach a t-piece and another gray 4 cm hose as instructed to the one hose you have.

step 6:

Attach a clear 4 cm hose to the top lug of the t-piece, similar to the instructions.

step 7:

attach clear hose from step 6 to center lug of switch

attach black 24 cm hose to left (bottom) lug of switch

attach black 28 cm hose to right (top) lug of switch

Replace the old actuator from the instructions with a new one and attach it to the axle so the lugs point to the *other* side! This will have the lugs point forward, away from the structure of the model, after the actuator is placed in it. This is very important!

step 8:

Replace the distribution block by a 2x4 brick of your choice (I used black). This is optional, but will give the structure more strength than leaving it open. Lead the gray hose through the second hole from the right side of the brick.

step 9:

Attach a t-piece to the gray hose with one of its inline lugs (not the top lug as instructed). Ignore the other hoses from the instructions as we don’t use the distribution block.

step 10:

Replace the red pump from the instructions with a new yellow hand pump. Then connect the pump directly to the other inline lug of the t-piece with a gray 4 cm hose. Attach a clear 2.5 cm hose to the top lug of the t-piece and connect it to the center lug of the switch. Do not attach any other hoses yet.

step 11:

Build as instructed.

step 12:

Replace the red 1x4 Technic brick from the instructions with a red 1x8 Technic brick and put it on the plate starting from the leftmost stud (see photo). Lead the two hoses from the first switch through the rightmost two holes of the new brick and to the actuator, with the left (bottom) switch lug going to the bottom actuator lug. Lead both hoses through the valley on the right side of the structure (see photo). These will be affixed later.

step 12.1-13:

Build as instructed.

step 13.1:

Build the excavator arms as instructed, but replace the two old actuators with new ones facing the same direction. Put an old gray 1x2 Technic brick with one hole at the other end of the center arm, so the arm has one brick on each end.

Note that it says on step 13.4 to use two half-width bushings with the smooth side facing outward to fix the 4 axle to the actuator. This does not make sense because the teeth of the bushings can’t properly interlock with the plates’ teeth unless they are pushed so far onto the axle that the two other plates attached to the bucket would bend. I recommend leaving the toothed side of the bushings outward for the actuator axle and not pushing them too far on the axle to prevent bending of the plates.

step 14:

Replace the 8 axle with a 10 axle and make sure to slide it into the structure so that the two hoses of the low actuator are under it. That way the axle keeps the hoses in place.

step 15:

Lead both hoses from the second switch through the next two holes of the brick, then through the arm as instructed and finally to the actuator, with the left (bottom) switch lug going to the bottom actuator lug. Attach two half-width bushings on the ends of the 10 axle holding the arm in place.

The instructions also tell you to place an old gray 2x4 plate seemingly on top of the hoses, while the next step shows the hoses on top of the plate. Because there will be two more hoses near the current ones later, I recommend leaving the plate away as it does not seem to serve a purpose.

step 16:

Attach a black 39 cm hose to the left (bottom) lug of the third switch. Lead the hose through the next available hole of the brick, below the two hoses of the middle actuator, and up along the right side of the lower arm.

Then lead it through the first brick on the center arm, between the two existing hoses, and push it along the arm through the second brick as instructed. Attach this hose to the bottom lug of the bucket actuator.

To construct the connection to the actuator’s top lug, you will need two rigid tubes of 4 cm length as well as black hoses of 5.5 cm, 16 cm and 18 cm length. Attaching the rigid tubes is done via four half-length pins with stud as well as four clamp plates.

The assembly looks like this:

Attach the black 18 cm hose to the right (top) lug of the third switch. Lead the hose through the next available hole of the brick, below the three existing hoses, and up along the right side of the lower arm.

Put two half-length pins on the arm’s beam brick and another two on the center arm, as indicated by the photos.

Clamp the two rigid tubes to two clamp plates each so they fit with the studs on the pins, and put the clamp plates with the tubes on the studs, attaching the tubes to the arms.

Then attach the 18 cm hose you laid down earlier to the lower tube, connect the two tubes using the black 5.5 cm hose, and finally connect the upper tube to the top lug of the bucket actuator with the black 16 cm hose.

step 17:

Ignore the red 4x6 plate as it cannot be attached.

step 18:

Build as instructed. You are done!

And this should be the result:

It might be possible to lay the hoses a little cleaner, but this is the way that involves the least customization (such as with rigid tubes) and still looks good. It also works perfectly! The model really packs some punch with the new actuators and also looks more modern. Constructing it is still very much a pain after attaching the arm to the structure (who came up with the idea of putting rubber bands on it in a place as inconvenient as this?) and leading four hoses on top of each other is quirky, but it’s worth the final product. The only design choice I could criticize is the strange skeleton of a cockpit. It doesn’t even sit on top of the structure, but is attached in line with it – that just looks weird from any angle other than left! And it doesn’t even have a floor.

Still, building this piece of Technic history was a nice challenge once again and the outcome even better than expected. Thanks for reading.

Looks great, must have brought back some feelings of nostalgia.

tim

Nice review! This sure was/is an awesome set.

A trip down memory lane

A very nice set! I hope I can bump one sometimes

Great mod... I might actually built it myself, since I've never owned this set.. but pretty sure I have all the parts to build it.. since I have the 8862 Backhoe (and I had the 8843, when I was a child)

I've always wondered why TLG decided to design the first generation of Pneumatics in such an awkward way. The suction is very weak, and the distribution block just adds to the complexity.

I'm trying hard to think of a good reason why the '2nd gen' didn't exist first?

RB

A good update. I'm working on moderninsing/updating an old set also. I actually have those old pneumatic parts but not the set.

H

8851 Excavator Review and Pneumatic Upgrade Guide

I recommend not to use half bushings because this ruins the well done design on the right hand side of the excavator - i recommend instead to move the axle completely into the hole and put a full bush on the left and put another full bush direct to the second right red beam (ie. between the rightmost beam and the second beam from the right)...looks way better and works pefectly.

It might be possible to lay the hoses a little cleaner, but this is the way that involves the least customization (such as with rigid tubes) and still looks good. It also works perfectly! The model really packs some punch with the new actuators and also looks more modern. Constructing it is still very much a pain after attaching the arm to the structure (who came up with the idea of putting rubber bands on it in a place as inconvenient as this?) and leading four hoses on top of each other is quirky, but it’s worth the final product. The only design choice I could criticize is the strange skeleton of a cockpit. It doesn’t even sit on top of the structure, but is attached in line with it – that just looks weird from any angle other than left! And it doesn’t even have a floor.

Still, building this piece of Technic history was a nice challenge once again and the outcome even better than expected. Thanks for reading.

Thank you very much for this very very well done update of a very good old technic pneumatic set! Just finished my build an apart from my recommendation above all funtions work very well and the original character of the excavator is preserved. so IMHO a perfect MOD.

Best regards

Hey, good suggestion about the half-bushes. Yes, your idea might look better. I've taken the model apart since writing this, so I can't check it out right now. Care to post a photo of how it looks?

Very nice but is there not a later version of this set with the newer cylinders?

Also u need too trim them hoses they look way too long and in ur face.

Nice mod by the way :)

Wow that's a nice mod. While i do have all the old pneumatic parts i might try this sometime just to know how it moves with the newer parts. I wonder if there's room for a compressor.

Wow that's a nice mod. While i do have all the old pneumatic parts i might try this sometime just to know how it moves with the newer parts. I wonder if there's room for a compressor.

There may be room in the cab,the model is very compact so it may be tricky.

Great topic. I always meant to do the same thing with mine. Glad to see it requires very few extra pieces.

instead of a 10 long axle i would use a 3 long, one 6 long and a connector.the 3 long should go through the cab side, the lift arm and into the connector. the 6 long goes through the connector out to the left side of the digger (seen from behind)

sorry, what is the code of "clamp plates" and "rigid tube" in the description:

"Clamp the two rigid tubes to two clamp plates each so they fit with the studs on the pins, and put the clamp plates with the tubes on the studs, attaching the tubes to the arms."? thanks

sorry, what is the code of "clamp plates" and "rigid tube" in the description:

"Clamp the two rigid tubes to two clamp plates each so they fit with the studs on the pins, and put the clamp plates with the tubes on the studs, attaching the tubes to the arms."? thanks

On Bricklink, the "clamp plate" is called "Tile, Modified 1 x 1 with Clip"; the "rigid tube" is "Hose, Rigid" which comes in various lengths (each with its own BL entry) and can be cut.

Edited October 28, 201311 yr by Hrafn

The 8851 pneumatic excavator is a very good example for a comparison of the old (1-hose cylinders) and the new (2-hose cylinders) pneumatic system.

I have build this very good pneumatic-upgrade version posted by MadMax in this topic.

And have compared it with the original one which uses the first 1-hose pneumatic system - here is the pic of both versions (left the original, right hand side the upgrade):

Well, from a pure aesthetic viewpoint one have to say, that the 1-hose system is way better (just imagine that the hoses can still be shortened a little bit but these are the length of the BI)

But if we come to performance than first such a comparison of two identical models with different pneumatic systems demonstrates what a huge leap forward the new pneumatic system is:

- way smoother

- way more powerful

- way more flexible - with the old one you can not simultanously open two valves in different directions

BTW: With this upgrade this is a very good excavator - only the look of the cabin is still a little bit "rough"....

Edited October 31, 201410 yr by Jim
Removed link to merged topic

I like this upgrade. :)

I have merged your new topic with the old one, to keep the information in one place.

Nice modification