Converting Märklin 3171, SJ D 109, to digital with Märklin conversion set 60903 or 60923, and adding close couplers
The 3171 is weathered with snow, otherwise it is identical to the Märklin 3170, the same locomotive without snow. In other words, this conversion may also be used for 3170 and 3670. 3670 was the digital version of the 3170. One version of the 3170 and 3670, from the very nice wooden train sets 2670 (digital) and 2870 (analog), had close couplers originally fitted.
I think that the chassis in Märklin model 3170, 3171 and 3670 (SJ type D, wood body) basically is the same as in Märklin 3018, 3019 and 3030 (SJ type Da, steel body)
My 3171 after the conversion
Preparations for conversion
Unfortunately, I have no photos of the inside of the locomotive before the
conversion started, as I did not think of a documentation at that time.
The motor and the reversing unit was removed, so were all the wires, except for
the black wire from the pick-up shoe contact plate to the power source selector
switch (to switch between current from the pick-up shoe or the pantographs).
All the mechanical parts remained in the locomotive, as this was practically not
used before the conversion. It is very important that all the gears and
axels rotate freely before the new motor is installed. Oil the rotating
parts very carefully, if required.
The contact tongues for the front and rear bulbs were carefully removed from
their brown plates.
Conversion sets
Both the older Märklin conversion set 60903, with a c91 decoder, and the newer
60923,
with an mfx decoder, can be used for the conversion. The only difference
between the two sets are the decoder itself. The motors and the small
parts in both the sets are the same.
Motor
The 3171 has a Small Flat Commutator Motor (SFCM), so the motor from the conversion set, Märklin no. 60903 (or 60923), was installed. I
cannot recall any difficulties with the motor installation. Make sure that
everything rotates freely before installing the brushes in the motor cover.
I have seen reports about a small problem on these locomotives, though. They
say that the rear left driving wheel hits the motor cover, and that 0,6 mm has
to be grinded off the cover, just below the rear noise suppressor in the below
photo. I did not experience that during my conversion.
Decoder
The decoder was installed at the same place as the old reversing unit.
I left it in the original cover and glued it to the locomotive chassis with some
detachable green stuff from 3M.
The functions:
| Function | Wire colour | Connected to | |
|---|---|---|---|
| f0 | forwards | Gray | Front headlight |
| backwards | Yellow | Rear headlight | |
| f1 | Brown/red | Center interior light | |
| f2 | Brown/green | Rear interior light | |
The locomotive inside after the conversion, with the original couplers.
Front lights
I pressed two new bulb sockets, Märklin part no. 624510, into the holes
where the old bulbs used to be. The photo is from another
locomotive. Then the 22 Volt bulbs 610080 fits perfect. If I find
the light is too intense, I often use 28 Volt T1 bulbs. The sockets are
not a part of the conversion set.
Interior light
I think that it is a waste not to use all the function outputs
of a decoder, so f1 and f2 was used for interior light in the locomotive.
One small bulb holder was glued to the decoder cover, another on the
motor. 28 Volt T1 bulbs are used, to get a dimmer light than the 22 Volt
610080 would give.
Close couplers
I prefer close couplers, as they give less free play between the units. If a
close coupler holder isn't available as a spare part, I modify the original
holders. In this case I
found two couplers, identical to the original ones, in my spare part box. I did not want to destroy
the original weathered once. One version of the 3170 and 3670 locomotive have close
couplers originally fitted,
but I have not been able to find their spare part number.
The original coupler. It is a little bit high, but very easy to adjust.
The original coupler parts, disassembled:
After disassembling, I cut the coupler at the red line, or, if I want the coupler to be a little bit shorter, at the yellow line, at the center of the hole.
The modified coupler (sorry about the poor sharpness):
I cut off the "flat part" of a Märklin 363950 coupler pocket. It is also a shorter available, no difference, as the flat part is not used. The remaining pocket is glued into the modified original coupler. The "ears" that held the old coupler parts are bent in to squeeze the pocket firmly to the coupler.
An original and a modified coupler:
The final result, after some fine adjustment:
The rear end of the locomotive, the small coupler hook on the bumper beam is
missing:
From below:
Some facts about the prototype:
| Power type | Electric |
|---|---|
| Builder | ASEA |
| Build date | 1925-43 |
| Total production | 333 |
| UIC classification | 1'C1' |
| Gauge | 1,435 mm |
| Wheel diameter | 1,530 mm |
| Length | 13,000 mm |
| Locomotive weight | 80.4 tonnes (steel) 79.5 tonnes (wood) |
| Electric system | 15 kV 16⅔ AC |
| Top speed | 70, later 75 km/h (Dg) 90, later 100 km/h (Ds) 100 km/h (Dk, Du, Du2) 110 km/h (Dr2) 120 km/h (Dr) |
| Power output | 1,220 kW (Ds, Dg) 1,660 kW (Dg, later) 1,470 kW (Dk) 1,840 kW (Du, Du2) |
| Tractive effort | 141 kN (Ds) 187 kN (Dg, original) 216 kN (Dg, later) 151 kN (Df, original) 161 kN (Df, later) |