DCC Loco Conversions - 3 - Worth the Effort? – Part 1 of 5

Discussion in 'DCC Control' started by Jim Freight, Jun 9, 2021.

  1. Jim Freight

    Jim Freight Full Member

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    Now I get to the primary purpose of this series of articles, examining the process of converting a pre-DCC loco to DCC operation, and ultimately is it worth the effort?

    Conversion of pre-DCC locomotives

    The issues to be assessed can be broadly grouped as follows, there is however, an unavoidable overlap between some of them as certain design features are inter-related :-

    Wheels and axles

    1) Axle tubes
    2) Wheel Bushes
    3) Steel Wheel Treads
    4) Serrated Wheel Treads
    5) Bronze or Brass Wheel Treads
    6) Rubber Tyred Wheel Treads
    7) Chrome Plated Plastic Wheel Treads
    8) Metal Plated Wheel Treads

    Chassis and Motors

    9) Pickups
    10) Wheel Arrangement
    11) Plastic Chassis
    12) Metal Chassis
    13) Weight
    14) Motors
    15) Lights

    I will now go through each of these in turn.

    Wheels and Axles

    1) Axle Tubes

    This is particularly important with locos from the 70s when split chassis design was in vogue, axles were moulded plastic tubes into which the wheels, fitted with stub axles were inserted. Over time these tubes often split whether the loco had been used or not. First indication on steam outline models can be that the wheel quartering is upset, a pair of wheels on an axle are no longer orientated rotationally at 90 degrees relative to each other. As it worsens it will cause the connecting rods between axles to jam on each revolution.

    Wobbling driving wheels can also indicate this defect, particularly when the stub axles are square, the only way to be sure about the state of the tubes is to totally dismantle the loco to inspect the axles, which is what you will have to do anyway to fit a decoder to such a loco.

    Converting split chassis locos can be fiddly so make sure those tubes are sound, no splits present or starting, if present replace them while you have the loco dismantled.

    This can also affect the gear train as at least one tube is likely to have a gear on it, a split all the way to a gear tooth root will jam the gear train as the spacing between two teeth will open up and it will no longer mesh properly with adjacent gear(s).

    This defect was most prevalent in the 1970s with Pailtoy Mainline and later the models transferred to Bachmann when Palitoy was bought out.

    Third party spares can be obtained from Peter's Spares, but note that Mainline and Bachmann derivatives often have different stub axle ends, circular or square and different gear ratios. Peter at Peter's Spare sells specific sets and will advise if you are unsure which you need.

    https://www.petersspares.com/

    2) Wheel Bushes

    Ever since model railways adopted two rail running with steel axles one wheel had to be insulated from the axle to prevent shorting out the track supply. Typically top hat plastic bushes were inserted into the rear of the wheels on one side and the assembled pair pushed onto splines at the end of the axle.

    Over time these bushes lose their flexibility, harden, and shrink, however the steel axle will not allow itself to be compressed so the bush eventually cracks and then splits completely. This results in no grip on the axle splines and wheels that can wobble and even slip rotationally upsetting the quartering.

    Older steam loco models from Tri-ang and British Trix were susceptible to this especially due to their present age. Some however still run true after 60 years, it's just luck.

    Minor looseness can be dealt with a touch of superglue providing the surfaces can be well cleaned, but that is often difficult due to oil and years of accumulated grime.

    3) Steel Wheel Treads

    The wheel tread is that part of a wheel which bears down on the rail, this can be angled or flat. Generally flat when rubber traction tyres are fitted.

    Plain steel wheel treads will need cleaning often but is tolerable, these were typical of the Tri-ang locos fitted with magnets for extra grip on steel rail, marketed as Magnadhesion. It's worth removing the magnets if possible to reduce drag on nickel silver track, otherwise leave in for extra weight.

    Also this era of wheels for Series 3 and Super 4 track will generally need their back to back increased for current Peco Code 100 points. Some may even have deep flanges that hit the sleeper chairs. I did not realise this until I had fitted a decoder to an old prairie tank that had die-cast wheels without steel tyres!

    A further potential issue is the angle of the wheel tread particularly with the Tri-ang diesel locos. Prototypically the treads are coned or better described here as tapered, larger diameter at the flange, smaller at the outer face. However I have had a few locos where the tread is either flat, i.e. no taper, or even negative such that the tread diameter is smallest at the flange. Although this does not make much difference to traction and power pickup the flat or negative treads combined with their substantial width will cause issues with some trackwork.

    I mostly use Peco Code 100 Streamline track with the occasional piece of Peco Setrack, the problem with wide flat or negative taper treads is that they bridge isolation gaps on a few items. Notably, diamond crossings both small and large, single and double slips, unfortunately these are available only as Insulfrog in Code 100. I have not noticed this issue with other Insulfrog points used in my main fiddle yard.

    This is not an issue with Electrofrog points as the whole frog is polarity switchable, the use of Code 75 track to use Electrofrog crossings may not be possible with vintage locos due to flange depth.

    It is possible to widen the isolation gap with e.g. nail varnish or similar painted on the rail surface but that may need replacing often due to wear and track cleaning. Also lengthening the non-conductive parts of pointwork becomes an issue with short wheelbase locos and diesel bogies.

    Your track layout design needs to take this into account if you intend to run vintage locos on DCC as a DCC power unit will quickly react to the monetary short circuit and shut down the track supply. A DC controller of days gone by fitted with a thermal cut out device would not trip on the momentary short, only a spark and momentary hesitation of the loco will occur as it rolls past the short.

    As an aside this shorting can also be caused by plated wheels of Wrenn rollingstock.

    Next, I continue assessing wheels, (4) Serrated Wheel Treads

    Jim

    Image: Tri-ang 3F with smoke unit (disconnected), fitted with a Hattons DCR-8PIN-HarnessMini decoder (my most frequently used decoder family).

    DSCF5733.JPG
     
    Last edited: Jun 10, 2021
  2. Dave C

    Dave C Full Member

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  3. Dave C

    Dave C Full Member

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    Jim. Interesting start.
    I have a Mainline Mogul with a split chassis and got a set of replacement axles direct from Bachmann at what I thought was a surprisingly low price (3 years or so ago now so can't remember). I admit I didn't check Peters Spares just on the basis of having phoned Bachmann and got a price below what I was expecting I didn't think it was worth checking elsewhere. However I have others to do in due course.
     
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  4. Jim Freight

    Jim Freight Full Member

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    Hi, I would prefer to get manufacturers own spares, but often they are defunct, the models just too old, or their spares department works on assembly area sweepings and returns broken down for spares.

    Hopefully the spares you received from Bachmann will fit but so far I have found spares for my Mainline Standard 4 were incompatible with the Bachmann split chassis version.

    Plenty more to come in this series of threads, please post your findings, Jim
     

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