Restoring a 6990 Monorail

[Plastikean]

Hello all, this is my first post to the EB forums! I've recently unearthed my childhood collection of Lego and am doing a little refurbishment on my 6990 Monorail Transport System. Since I was pretty OCD about my sets at that age, and since my parents packed things away pretty attentively during my Dark Ages, the set is in outstanding condition. I thought I'd share some of the experiences I've had, and some questions that arose, as I've been rehabilitating it.

Parts

There was only one missing piece in the set, a simple white 1x2 plate, so no problem replacing that. Also, the set has only 7 of the large supports, enough to build the main model—but the online inventories say there should be one extra, for a total of 8. I don't recall there ever being an extra; was this included in later editions of the set? Right now I am considering the set complete with 7.

In building the set, I broke one of the white antennas because of the very tight fit of the trans-red dish onto it. Again, this was easy to replace (I got two in case the other one ever breaks.)

Other than the 8th support, I have all the various extra parts that came with the set: the different 1x1-size parts, trans-blue minifig visor, trans-red light cover, etc. I even have an extra white 1x4 brick for some reason. Was this a genuine extra part, a factory packing error, or did it just get mixed into my set by mistake?

My biggest challenge is with the electric connector wire. This set came with the rare plate-sized connector, which has small clips on the underside of its plate ends that cover the electrical solder as well as providing the clutch power for the bottom. The tab that holds this clip onto the plate itself is very tiny, and with age the plastic seems to degrade so that these tabs break off and the clip becomes loose. It will often be pulled off by the act of disconnecting this part from the battery box studs. (The same degradation results in tiny cracks forming in the plate ends, which must be why so many of these listed for sale have corners or edges missing. My part has the beginnings of these cracks, but so far the damage is minimal.) This photo shows the underside of the part, both with and without this clip:

I am currently sourcing replacements for this, but there are very view for sale and most of those seem to be in worse condition than my own. I'm wondering if I'm better off just gluing the clip back in with a plastic cement; has anyone else ever dealt much with these vintage pieces?

Yellowing

As you'd expect, many of the white and grey parts in this set had yellowed, but I've had good luck reversing this. After reading about numerous un-yellowing methods of varying complexity, I'm glad to say I've had good success with a simple 3% peroxide solution in direct sunlight—no added OxyClean or higher strength peroxide solution—and most parts have returned to white in a few hours. I'm using clear plastic containers, and I'm sure it helps that I have a white table outside to put them on. I made a quick cornstarch & peroxide paste for the battery box, since it can't be submerged, and the large baseplate, which is too big to dip.

A few parts showed more resistance to de-yellowing: the webbed radar dishes needed some extra time, and for some reason the 1x1 cones as well. The soft plastic of the flexible hoses did not respond to the treatment, but the end pieces did, so these are now a two-toned affair. I'm currently re-dipping the long Technic rack pieces; these almost look like they turned more yellow. Are they a different plastic, and should I be using a different technique for these?

Meanwhile, a couple of parts (the rack winder and the motor housing) never yellowed and are still completely bright white—they must also be a different plastic—and so I'm using them as my color comparison to the treated parts.

EDIT: One of the straight track pieces, which was significantly more yellowed than the rest of the track, ended up suffering some fading and is now a bit of a chalky white on the top and one side. I knew this was a possibility with light grey parts, but even though I was getting the yellow out within a few hours of treatment, I somehow assumed that the bleaching problem wouldn't happen that quickly. Of course, it had to be the relatively rare (and thus expensive) straight track, so it will cost I bit if I decide to replace this part. :-(

Packaging

As far as I can tell, I have the complete packaging save for the original polybags. I have the outer box top and bottom, red inner box, four plastic inlays and a plastic inlay lid. I even have the cardboard space backdrop and the original catalog that came with the set. The instructions are in excellent shape, too: only the outer leaf (cover and fold-out back page) has separated at the staples, but the booklet itself is otherwise undamaged.

Overall

Of course I checked the electrical function and everything works perfectly—although I went through three 9v batteries that I had in my drawer before realizing that every one of them was dead; it wasn't the monorail! A trip to the store and one new battery later, all was well.

I have not yet decided if I will try to sell this set or keep it in my collection. I believe I can get quite a good price for it as the condition is excellent and the set is 100+% complete. Then again, I might hang on a bit and see if the price goes up a bit over time. :-)

Thanks for reading, and I'd love to hear about others' experience restoring this set or with some of the issues I've found. Meanwhile, my next project will probably be the 6285 Black Seas Barracuda, arr!

Edited August 23, 2016 by Plastikean

[CP5670]

I have two copies of the set and the specific pieces you mentioned are definitely more yellow than the others (which still look white). The soft plastic they are made of seems to be more prone to yellowing. Those 1-height 9V wires are indeed fragile, which is probably why they were replaced after a few years. On mine, the plastic on top of the studs is coming off, but the plate edges are holding together. Later versions of the set (1990 onward) actually had the regular 2-height 9V wires, which fit in just fine.

There are 8 large supports but you don't really need all of them, especially on the curves.

[Plastikean]

Those 1-height 9V wires are indeed fragile, which is probably why they were replaced after a few years. On mine, the plastic on top of the studs is coming off, but the plate edges are holding together. Later versions of the set (1990 onward) actually had the regular 2-height 9V wires, which fit in just fine.

Yes, I'll keep the 2-height version in mind as a Plan B, but I would prefer to keep the set to its "original equipment", if you will.

There are 8 large supports but you don't really need all of them, especially on the curves.

Right, the official model only calls for 7, but you might need 8 if you were expanding or doing a different track configuration. But were there sets that never came with the extra 8th support, which is what I suspect I have? Or do I really need to buy another to consider the set "complete"?

[1980-Something-Space-Guy]

May I ask how the yellowing on these pieces happened to you guys? I have had one of these sets for around 5 years. It's stored in a plastic box inside my closet, so that it is exposed to no light. Is that enough?

Also, my Technic Space Shuttle suffered breaking of the rubber in the 9V wires. This happened too with some 9V wires I had stored for about 10 years. Does this happen to the cables of this set? Incidentally, does that happen to 6991 as well?

[Plastikean]

May I ask how the yellowing on these pieces happened to you guys? I have had one of these sets for around 5 years. It's stored in a plastic box inside my closet, so that it is exposed to no light. Is that enough?

For my part, I really can't be sure. When the set was new, I would have had it displayed for a few years, in the open but never in an especially sunny place that I recall—though it may have lived closer to a window than other sets I had at the time.

After that, it would have been stored away in its box for twenty years or so—in more than one location, to be sure, but never anywhere close to the sunlight or even much artificial light. And the pieces weren't uniformly yellowed, just certain pieces and on certain sides of them, as if it only affected the top layer of parts, say. I wasn't really around during this period, so I suppose it may have been subjected to some light (and maybe the plastic packaging did something to amplify the effect), or perhaps UV radiation can penetrate boxes in a way that visible lights can't. But it does seem likely that age alone can have some yellowing effect regardless of whether the set is packed away, although certainly less than if it's left in the open.

Also, my Technic Space Shuttle suffered breaking of the rubber in the 9V wires. This happened too with some 9V wires I had stored for about 10 years. Does this happen to the cables of this set? Incidentally, does that happen to 6991 as well?

I have heard of this happening, but it didn't happen to mine or any of the spares I've tried out so far. (At least one of those doesn't work electrically, but it's not due to any visible defect.) I would definitely guess that this is more likely in a part exposed to sunlight than one that is packed away.

[bonox]

Also, my Technic Space Shuttle suffered breaking of the rubber in the 9V wires. This happened too with some 9V wires I had stored for about 10 years. Does this happen to the cables of this set? Incidentally, does that happen to 6991 as well?

there seems to be a mix wire insulation; some are rubber and some are plastic. They both have the plasticisers and 'liquids' evapourate out of them over time and they become brittle and just fall apart. The rubber version in my experience is much worse than the plastic version.

You might be able to improve their life by storing them in a strange high chemical humidity environment to stop the insulation drying out, or you might be able to apply rubber protector over time, but you're probably better off just getting some practice in replacing the wire. It's not that hard to get the clips apart without breaking them, and you have the added advantage of being able to make the replacement any length you like.

[1980-Something-Space-Guy]

For my part, I really can't be sure. When the set was new, I would have had it displayed for a few years, in the open but never in an especially sunny place that I recall—though it may have lived closer to a window than other sets I had at the time.

After that, it would have been stored away in its box for twenty years or so—in more than one location, to be sure, but never anywhere close to the sunlight or even much artificial light. And the pieces weren't uniformly yellowed, just certain pieces and on certain sides of them, as if it only affected the top layer of parts, say. I wasn't really around during this period, so I suppose it may have been subjected to some light (and maybe the plastic packaging did something to amplify the effect), or perhaps UV radiation can penetrate boxes in a way that visible lights can't. But it does seem likely that age alone can have some yellowing effect regardless of whether the set is packed away, although certainly less than if it's left in the open.

I have heard of this happening, but it didn't happen to mine or any of the spares I've tried out so far. (At least one of those doesn't work electrically, but it's not due to any visible defect.) I would definitely guess that this is more likely in a part exposed to sunlight than one that is packed away.

Hmmm, well, I can only hope my parts don't get too yellow!

Regarding the cables, believe it or not, my Space Shuttle was never exposed to the sun, nor did the cables I had stored. All I can think of is it could be humidity, since I lived in a humid place.

there seems to be a mix wire insulation; some are rubber and some are plastic. They both have the plasticisers and 'liquids' evapourate out of them over time and they become brittle and just fall apart. The rubber version in my experience is much worse than the plastic version.

You might be able to improve their life by storing them in a strange high chemical humidity environment to stop the insulation drying out, or you might be able to apply rubber protector over time, but you're probably better off just getting some practice in replacing the wire. It's not that hard to get the clips apart without breaking them, and you have the added advantage of being able to make the replacement any length you like.

This does sound like a good long-term solution, especially now that I seem to have almost no spare 9V wires... I just hope that when I am able to replace the cables, that I can find a wire that is close to being as flat as that in the set, so it can go in those small holes that the original cable used to go through.

[Plastikean]

You might be able to improve their life by storing them in a strange high chemical humidity environment to stop the insulation drying out, or you might be able to apply rubber protector over time, but you're probably better off just getting some practice in replacing the wire. It's not that hard to get the clips apart without breaking them, and you have the added advantage of being able to make the replacement any length you like.

Are we talking about the same part? I can't imagine being able to get the clips apart on my plate-height connectors; indeed, most of the connectors I've seen are already cracking and the bottom clips already broken. But I guess you're talking about the 2x2x2/3 version, huh? Perhaps those are less prone to crumbling than the 2x2x1/3!

[bonox]

i've only taken apart the 2/3 stud height version. I imagine the 1/3 model is more tricky but no different in concept. I've also modded a few of mine and chosen to solder the new wire to the insides rather than try to reuse the old knife edge insulation penetrators. Doing so gives me a much wider choice of modern wire.

[Plastikean]

i've only taken apart the 2/3 stud height version. I imagine the 1/3 model is more tricky but no different in concept. I've also modded a few of mine and chosen to solder the new wire to the insides rather than try to reuse the old knife edge insulation penetrators. Doing so gives me a much wider choice of modern wire.

OK. I wouldn't be concerned about the method, just that the piece wouldn't survive the operation, given that so many of the 1/3 height are found with edges and corners cracked and crumbling. The piece is just so brittle that I wouldn't expect to be able to do much surgery on it without pretty much destroying it.

[rodiziorobs]

I can't speak to the electrical components, but the yellowing of the parts in question isn't a matter of light exposure, but of oxidation. That's why it happens whether you display them or not (although UV exposure will accelerate yellowing).

The yellowing is actually the surfacing of bromide compounds that used to be present in the ABS mixture (I believe it was for fixing the color from when Lego sourced their plastic from Bayer), and is reversed with the peroxide treatment mentioned above.

Good news is Lego changed its recipe sometime in the 90s, so bricks from later than that do not exhibit the same oxidation yellowing.

[1980-Something-Space-Guy]

I can't speak to the electrical components, but the yellowing of the parts in question isn't a matter of light exposure, but of oxidation. That's why it happens whether you display them or not (although UV exposure will accelerate yellowing).

The yellowing is actually the surfacing of bromide compounds that used to be present in the ABS mixture (I believe it was for fixing the color from when Lego sourced their plastic from Bayer), and is reversed with the peroxide treatment mentioned above.

Good news is Lego changed its recipe sometime in the 90s, so bricks from later than that do not exhibit the same oxidation yellowing.

But modern bricks to suffer yellowing by UV exposure anyways, right?

That's really disappointing to hear. I used to think that storing the sets away from light was enough to prevent them from yellowing. I'm assuming the fix is only temporarly, and that the oxidation will happen again eventually?

[TheLegoDr]

^That is my understanding, although I don't know how long it takes to become yellowed. I've had success with peroxide in the sun. It doesn't take away any scratches, but does make it whiter in appearance for sure.

[Plastikean]

^That is my understanding, although I don't know how long it takes to become yellowed. I've had success with peroxide in the sun. It doesn't take away any scratches, but does make it whiter in appearance for sure.

Yes, and in my brief experience so far, the process is much easier and quicker than you might predict from reading about it.

Curiously, if it's due to oxidation rather than light, why would parts tend to yellow on a single side rather than all around?

[1980-Something-Space-Guy]

Yes, and in my brief experience so far, the process is much easier and quicker than you might predict from reading about it.

Curiously, if it's due to oxidation rather than light, why would parts tend to yellow on a single side rather than all around?

Well, in the case of the monorail tracks, they are made of several separately molded pieces of plastic. Perhaps coming from different batches causes different rates of yellowing.

In the case of regular parts (made of a single mold) I have never heard of yellowing only happening on a single side when it wasn't due to the sun.