Picture 1 - A foretaste: Roco's E 71 in service on a Märklin layout

The prototype entered service as a Prussian State Railways (KPEV) freight train engine in 1914. The construction prooved well, so that these engines stayed in servece until the late 1950ies. Due to a conversion for a higher maximum speed, these engnines could also used for passenger trains later on. The E71 should be one of the smallest "crocodiles" ever built. Three engines have been preserved, one in the Traffic Museum (Verkehrsmuseum) in Dreseden, one in the DB Museum in Nuremberg, and one in the German Technique Museum (Deutsches Technikmuseum) in Berlin.

The only one large-scale produced model of this engine was offered by Roco from the late 1980ies until somewhere in the 1990ies. Its detailing can still satisfy today's reqirements, however it has no flying wheel, there's no room for a decoder, an there are no NEM coupling shafts. Roco produced several versions of this model: DRG, DB, however, never any AC version. The models are often offered second-hand.

You can load the pictures in this report in their original size (only exeption: Picutre 1) - just click on the the pictures!

The requirements for my conversions are to get a model which runs smoothly and free of derailments, the appearence however, shouldn't be disturbed. My layout is partially still equiped with Märklin M-tracks, especially the curved turnouts and double-slip-turnouts are well-known for their specific demands for the wheel sets' characteristics. My experiences showed that it is impossible to use the original Roco DC wheels, even if the wheels are pressed togehter to a 14,0 mm gauge. So it is a principal duty the exchange the wheels.

Moreover, my tracks are weathered - which requires a good power take off an and good running characteristics, missing flying wheel can become problematic.

I tried the conversion of my E71 in two "steps": First I tried to keep the original motor and the lightening an fitted a decoder, which however satisfy me. During the second step, the not smoothly running  motor was replaced by a Faulhaber motor, and the lightening was isolated from the frame; finally a Kühn T145 Decoder without any interface connector was fitted.

The following conversion steps were taken:

- Creating room for the installation of a decoder

- Exchanging the wheels

- Removing the gears from one bogie and installation of a pickup shoe on this bogie

- Replacing the original Motor by a Faulhaber motor

- Isolation of the Lightening

- Fitting a decoder, complete new wiring

The locomotive has to be completely dismantled. If anybody doesn't posess the original instructions, he should follow my descriptions, because the locomotive has been assembled using many "tricks", like it is typical for Roco. Before starting, it is helpful to take some pcitures from all sides of the model, so it will become easier to re-assemble the model later on. 

We should note that both front parts are not identical, so when reassembling the model, it must be sure the right front part ist mounted on the front side. Moreover we have to regard the mismatch of the counterbalances. The unscrew the coupling rods, we need a very fine wrench.

Disassembling the locomotive is done as follows: First all seperate plastic parts of the locomotive are removed. Then we draw off the roof of the middle section upwards. Afterwards both driver’s cabs parts are spread from below and drawn off upwards. Both front parts drawn off forwards. Both plastic parts on the bottom of the locomotive between the bogies must be drawn off. The screws for the bogies are hidden in the front parts of the locomotive. We unscrew them by putting a small screwdriver through the hole beside the gearwheel in the bottom of the bogies and try then so long, until we can unscrew the screw (Picture 2). Both bogies are drawn off.

The front bogie, on which we will mount the pickup shoe, is being disassembled as follows: The plastic covering of the worm on the top of the bogie is being removed and the worm is taken off. The coupling rods are unscrewed. The bottom of the gear box is being removed, so the axes fall out. The plastic covering for the blind wheels are removed and the parts with the wheel contacts are dismantled. The metallic part of the bogies exists of two “bowls” which should fall apart now. The gears can be taken out. The rear driven part needn’t be disassembled completely. It’s enough to remove the coupling rods and the bottom of the gear box, and to take out the axles.  The holdering for the light bulb should be snipped off. The main board becomes fully visible if the bogies have been taken off. The electric connections with the bogies and with the lighting are desoldered. The board is being unscrewed and we can take off the motor. The contact spring to the motor on the board is also desoldered. The windows of the middle section of the locomotive should also be removed. Now, the locomotive has been nearly completely disassembled into its single parts  We have to pay care that no small parts get lost – to reassemble the engine later on, we need in fact nearly all parts again!

Picture 2

One of the reasons, why the locomotive should be disassembled completely, is the crude procedure necessary on the metallic middle section of the locomotive, in which the room for a decoder must be filed or milled. Pictures 3 and 4 (after the assembling of the interiors with the front parts) show how the decoder was placed on top under the roof of the front control panel.

The T145 decoder is relatively narrow and low (13.9 mm x 24.6 mm x 2.9 mm), but relatively long, so that he fits just in the prepared place. Smaller decoders need of course less work.

When filing, we have to pay attention to the fact that the outside edges are not damaged - one would see this later. Other electric works were not carried out in this early conversion stage.

Picture 3	Picture 4

In my judgement, the exchange of the wheels is a key for a sucsessful conversion. For the E71, I had the advantage to posess the Roco model of the BR 93 steam engine, and comparing the the sizes of the prototypes, I found out that both locomotives' wheels had the same diameter. Moreover the small counterbalances are exactly the same. Because the BR 93 ist offered as an AC version, it was no problem to order the fitting wheels of this locomotive as spare parts.

By this time, it was already clear that the gears of one bogie had to be removed, i.e. the bogie would become undriven. So decided to equip the remainung driven bogie with four traction tires. So

Because of this, we only need the 2nd an 4th driving axle of the BR93, each twice. The ordering numbers are 106873 and 106871. The AC version of the BR 93 is offered in the current Roco programe (4/06), so it shouldn't be any problem to get the spare parts.

The old DC wheels are removed, and the new AC wheels are pressed on the axles. Please pay attention to a correct mismatch for the coupling rods - if one doesn't work precisely enough, the motor will clamp and the locomotive willrun very unsmoothly. The interior gauge must be 14,0 mm. Before the wheels are mounted in the bogie, they shold be painted with red colour (Revell matt 36), to get rid of their ugly plastic lookout. Another particularity is the axles of the blind wheel: this axle is driven, from where the driving axles are driven via gears. In the now undriven bogie, the gears have been removed. However, the axle of the blind wheel ist still so thick that it comes into conflict with the holdering for the pickup shoe. So it has to be milled off in the middle. Unluckily I don't posess a lathe, so helped myself, by clamping the axle (without the blind wheels, of course) into a drilling machine and it "milled" the middle part more thinly then with a file. Please note: the outer parts of the axles, on wich the blind wheels are mounted, musn't ne damaged - one would see that later on! Picture 5 shows the bogie with the removed gears and the milled-of axle of the blind wheels (the old motor was only put below the bogie to hold it for the photo).

Picture 5

 A little bit external-concentric another 2-mm hole was drilled, to be able to screw or unscrew the screw holding the bogie, from there. This admission plate was stuck with Stabilit glue thus into the opening of the bottom covering. When the glue has hardened, the bogie can be reassembled, however without all gear parts. Power take-off on the front bogie, however, is quite important due to the traction tyres on the rear bogie. So we have to regard that really all wheel contacts touch the wheels! It is advisable to solder the little wires for the mass contact again on the bogie. The rear bogie should keep its ground contact for asafety's sake. The originally separate contacts on both sides of the axes should be conncected with a wire.

 After assembling of both bogies and the installation of the axles, the coupling rods can be mounted. Besides, is to be noted that the drilling for the blind wheel is located a little bit external-concentric. Therefore, the coupling rods must be screwed on in such a way that the thicker side of the connection points in the blind show upwards.

The SB-Modellbau conversion kit # 28011we used can be mounted according to the matching description. In addition only the attached brass part is stuck from below with 2K glue into the middle section. Be careful with glue and don’t use too much of it. Before I went on following the instruction and glued the motor into the brass part, I soldered two connection wires to the motor, and fitted some isolation tape into the shell, to prevent the motors connections from touching the shell, which has ground contact. Decoders never forgive this kind of contacts…  Picture 6 shows the position of the motor the locomotive’s middle section. The motor itself was not changed, i.e., also the side without gears in my engine, has still its cardan bearing. After installation of the engine the main platinum can be screwed on again. Because the conversion kit uses cardan shafts instead of the Roco springs, the spring bearingt has to be removed and the cardan bearing must be pressed on the worm of the driven bogie. Like described in the instructions, we should mount the driven bogie for a test with cardan (should be screwed together on the middle section) and check the run. Should there be any jarring noise, displace the cardan bearing on the bogie. Already now, the soldered connection wires of the motor have proved, by the way, excellently.

Picture 6

The original lighting was grounded via the shell.To avoid the flickering light resulting from this, the bulbs were isolated. I have not used the original light bulbs any longer, but the Märklin plastic holderings 604180 and the matching bulbs 610080. The openings for the old Roco bulbs must be drilled off a little bit, before we can install the #604180 holderings.

It is advisable to press together both gear parts with a small vice. Little wires were soldered to the holderings and the contacts isolated with shrink tubes. Before we shrink the shrink tube, we should bend the wires backwards, because there isn’t unlimited room below the “hoods”.

Both bogies have been assembled now, the test has been passend well, the light isolation is connected. The bogies should be already screwed on the middle section. Isolate the room for the decoder with isolation tape oder paper, to protect it from electrical contact with the metal shell. Now we can start with the electrical works. Both motor connection wires are soldered on the conatacts of the board (please note: avoid any ground contact!) The ground wires of both bogies are soldered thus on the board, that one of both fixing screws of the board functions as an electrical connection to the middle section. Now the connection wires of the decoder for the ground and the motor are cut into the right length and soldered on the board. In this state the bogies can be screwed with the the middle section. The connection wire of the decoder for the pickup shoe is threaded directly through the front bogie and is put through a hole into the pickup shoe’s holdering. I have soldered it directly on the pickup shoe; however, with an additional contact plate one could also solder it on the pickup shoe’s holdering.  The lamps are wired with the decoder, the white wire to the front lamp, yellow to the rear, the ground the violet connection of the decoder. All solder joints of the wires were protected with shrink tubings against any contact with other metal parts. Picture 7 shows the final condition.

Picture 7

A frequent problem of such conversions is the fact that the light change does not square with direction of the travel of the locomotive. In this case the motor connections must be interchanged.

 To change the lighting, would be a laborious thing with the E 71, because in addition, at least one of the bogies must be unscrewed again. So, the hole in the holdering of the pickup shoe shows its advantages soon.

 After the conversion, power take-off is only possible via the tracks, i.e. the center rail. Power take-off via catenary wire doesn’t really make sense in my eyes. If anbody wants this, nevertheless, the suitable cables must be soldered – there is no place for a manual lever!

All interiors are installed now - only the parts of the shell are still missing. Now the time for the test runs has come - before however, one should check if the decoder has been connected correctly. A good way is the programming track of the Intellibox, which is signalling short circuits. If everything is ok, the test runs can start. If there are problems - for example the model runs unsmoothly, or buckling, or something else, we proceed like described above - unluckily, a partial dismantling of the eninge becomes necessary in this case.

Pictures 8 und 9 were taken during the test runs.

Picture 8	Picture 9

At last, all parts of the shell and the extra parts, which are typical for Roco, are being mounted. We just work reversly like during the dismantling - at that time, we collected so much experience with the locomotive's structures, that the re-assembling should be done quite easily. Thanks to online programming, the decoder can be programmed already during operation. 

Allthough this is not a convesion to be done by beginners, it also isn't extremely difficult. However, many single steps are necessary to achieve the aim. During several steps, like the exchange of the wheels, work has to be done very carefully and exactly. All parts can be ordered via the model train manufacturers' spare part service. So I also recieved the wrench to unscrew the Roco screws of the coupling rods.

The largest disadvantage, however, are the high costs for the Faulhaber conversion kit, which, however, if we regard the results, offers the best solution for smooth driving characteristics and high traction power.  Using a whisper pickup shoe, there wouldn't be in fact any noises being caused by this engine.

Perhaps it's of interest, if someby else found a cheaper solution to replace the old motor by a standart motor. However, it must have a flying wheel - but we shouldn't waste time with the original motor..

The model with a lentgh of only 13,3 cm and a weight of 320 g, runs over all track combinations, turnouts, an through narrow curves and has enough traction power to haul several freight vars, or a coupke if "Donnerbüchsen", over the ramps. Because of the long time its prototype remained in service, and the large range its service, it ideal for model railroaders. Moreover, it's an eye-catcher on the layout and interesting for everybody who like old electric engines.

Picture 10	Picture 11

 Pictures 10 and 11: The E 71 in service

Disclaimer: all steps shown in this reports, are the procedures choosen by the author. Neither the author, nor the webmaster of this page, can be held responsible for any damage you do, by modifying your model railway equipment. What you are doing, you are doing it on your own risk.