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Z Scale Layout – Reviving A Marklin 8852 Krokodil

This poor thing came to me from Yahoo Auctions Japan in the first bundle'o'stuff. I threw it on the rails and it just sat there, dead as a doornail. Actually, I lie, I saw the headlights flicker once. Fortunately I paid only half the current going rate to versions showing on eBay now. Of course, that may be because this is an older variant.

The train was then thrown on the test track and still chose not to respond...

I had a quick squiz of the manual above and realised that the unit had a switch to select between catenary and rails...

But this also proved fruitless. The train was therefore stored back in its box for another day when I had the courage to try and service it. Around a week ago, that day arrived and I dismantled the loco.

Open-Train Surgery

The plastic shells come off with ease. Remove the main shell first, followed by both bogie shells.

The bogies are secured to the chassis by their axles, which are actually kept in place by the main shell. The axles hold a gear in between the bogies and main chassis which transfer the power from the worm gears.

A quick look at the motor saw that it was in need of love. I carefully extracted it and un-sprung the brushes. They looked OK, but the contacts on the armature were tarnished. Cleaning these and reassembling the brushes saw the engine come to life, but still very erratically.

At one point the motor jammed when I wasn't looking and melted the contact off a brush. I attempted to solder it back on, but I couldn't get a precise location and the motor kept stalling and melting the solder I applied!

So. I started searching for brushes and found some on eBay... Which are still crossing an ocean from Italy somewhere. The joys of European models! I then stumbled across a page indicating that these older models had an optional 5-pole motor upgrade! Of course, the motor I needed was absolutely sold out and unavailable.

A lot of emails and searching later, I did the unthinkable: I actually clicked on the second and then third pages of Google search results! I then doubled down and opened a pdf result... To only find success! Nathan's Trains in QLD had five of the motors I needed in stock! And also brushes for the old motor. I bought both and they arrived in no time. I'd personally like to thank Noel at Nathan's Trains for stocking these vintage parts and providing great service.

The new motor went in very quickly and easily, but the bogies were still jamming pretty badly. In fact, one wouldn't even complete a full revolution with the axle in, regardless if it was mounted to the chassis or not! At this point, after resoldering a few wires which had broken from twisting the components around, I went all-in and disconnected the bogies from the chassis to do a full service and alignment.

Just like the actual Lego Krok that I built (see the end of this post), these wheelsets need the driving rods at 90-degrees to operate and I had a feeling they were both out. The electrical pick-ups were also showing over the top of the drivers and not behind them, where they should have been. Trying to work on these with the chassis strung on by the wiring was proving impossible. With the bogies separated, it was very easy to then roll them on the bench top, align, roll, align, test and repeat until the were totally in-binding.

Note that there's really only one way to re-assemble these bogies. The driving wheels are permanently connected to the driving rods and the rods have a secondary 'fake' rod that makes orientation easy. If you scroll up to the pic of the side-on Krok with just the chassis shell, you can see that the bogie on the right has the drivers installed upside down. The 'extra' rod is hanging so low it hits the rails on each revolution!

I reckon I re-assembled both bogies around 10 times each. There's around 7 gears per unit and they're VERY fiddly. The electrical pickups are sprung behind the drivers and actually push them down when you're trying to force them in. Trying to align it all takes great patience! There was even a chunk of (what looked like) solder in one of the bogies that was causing the gears to jam... no wonder.

In the end, patience, grease and minute adjustments saw both bogies re-assembled and rolling smoothly on the table. The new motor was mounted in the chassis and the only real point you need to know is to push the motor ALL the way down into the chassis. It's easy to let it sit a 1-2mm too high... and if this happens, it'll fail to make proper contact with the bogies.

Finally, the wiring... It's slightly complex with the overhead caternary switch, but I re-soldered it all, failing to note how the directional headlights were wired... so... instead...

LED Headlights

It now has a 5-pole motor... the least I can do is give it a beautiful headlight. I found that the unit was really only running well in one direction (after all my hard work), so I set about removing the incandescent grain-of-wheat bulb and replacing it with an LED. I found a 3mm white LED in my box'o'junk and slapped on a 780ohm resistor. I then cut the legs ridiculously short.

The existing light housing and contacts were removed and one LED leg and the other resistor leg were soldered to the tabs on the wheel pickups. Once in the correct direction, the LED lit up when heading forward!

A little bit of adjusting saw the shell fit back on!

Internal Model Clearances

I just need to point this out, as I had a lot of trouble at the end. It turns out that the solder blobs I put everywhere were actually millimetres too high and causing the shells to not actually clip onto the frames! Easily fixed, remove the solder. I just had never thought that the clearance would actually be that low.

Above, a reference shot for your future soldering nightmare.

My Lego Krok

I eluded to this before.. and I really can't believe that I haven't featured it on here before. It's a Lego version of this locomotive and it arrived for my bday last year.

What a tiny Z-Scale loco!