DCC Loco Conversions - 40 - Tri-ang Hornby Hymek R.758 1968

Installation of a decoder is straightforward as there is plenty of space, modifying the power bogie to insulate the original brush holder takes a little longer. Providing extra power pickup axles and increasing the overall weight of the loco makes for a much better runner.

Very Important - the power bogie was modified as in article 39, failure to do so can destroy a decoder.

https://platform1mrc.com/p1mrc/index.php?threads/dcc-loco-conversions-39-tri-ang-hornby-power-bogie-x-3710-x-337-x-213.6116/

This early version of the Hymek is quite robust compared to its Hornby successor, it relies on weight and traction magnets for traction rather than tyres which harden, create dirt, wear out, and reduce the number of wheels available for power pickup. However the traction magnets are of no use on nickel silver rail but traction can be regained by adding weight.

The decoder is to be fitted at the opposite end of the loco to the power bogie to simplify the wiring in the spacious bodyshell of the loco. Connections between wheels, motor and decoder were to be centralised.

First I prepared the wiring before connecting the motor, decoder and pickups together.

Power Bogie

Two holes were drilled in chassis moulding that surrounds it, one for wires carrying track power and the other to carry motor drive power.

PTFE insulated multi-strand wire (30 AWG 7/38) was chosen for this loco as it has a thin tough insulation which makes it easier to route around a loco like this whilst having a very good conductor cross sectional area for its diameter.

The contact plates at the commutator end had already lost the retaining pips when I bought this loco, drilling to replace them with self tapping screws failed as there is little material there and the housing plastic is brittle. So I tied them down with nylon cored lacing cord.

Wires were then attached to the power bogie, ensuring they were long enough to allow release of the power bogie from the chassis for maintenance without having to disconnect them.





Extra Pickups

I consider this as essential for DCC, one 4 wheel bogie is not enough so I replaced the original wheelsets fitted to the unpowered bogie with Hornby 12.6mm disc metal wheelsets so that all four wheels could be used for power pickup.

The power collectors are made from phosphor bronze strip attached to single sided Vero pins which are soldered into a piece of Veroboard and reduced in height once the pickup strips were fitted.

The board is held to the bogie with double sided sticky pads, normally I would use self tapping screws but the plastic parts on this loco are a little fragile.

Wires for each pickup are routed up through the tubular rivet retaining the bogie and emerge from under the factory fitted ballast weight via a useful gap between the weight and chassis.



Central Wiring Connections

Another piece of Veroboard with 4 single sided pins soldered to it provides the centralised connection point, this is fixed with a longer than original weight retaining screw with some insulation material (yellow) salvaged from an old H&M controller to stop the pins shorting against the metal weight. The tracks of the Veroboard have sections removed such that none can be shorted by the weight retaining screw.

The wires from the extra pickups were first attached to the pins, followed by the motor bogie wires, note that each connection on a pin is kept discernable from another and individually removable, do not try and solder them all as one as you run the risk of big blob bad joints.



Fitting a RoS-218 Decoder

As there is plenty of space in the body shell I have used the bulkier RoS-218 decoder which is supplied with a harness mounted 8 pin connector, physically larger with even more functions I do not need but easier to connect and the same price as the RoS-6D.

Necessary wires, red, black, orange and grey soldered to the top of the centralised pins, surplus wires have been sprung from the connector housing.



Extra Weight

As the traction magnets will be ineffective on nickel silver rails I have increased the chassis weight in two places, two blocks of lead in the power bogie cab end, and strips of lead formed into a rectangular U shape in the centre of the chassis. This has been wrapped in Duck tape for easier and cleaner handling later as a single block, additionally the tape helps to gently wedge it into position.





The gross weight of the loco is now 334 grams, distributed 238g over the power bogie and 96g over the unpowered bogie, there must be sufficient weight on the unpowered bogie such the pickup strips can be set to make good contact without the wheels skidding.

The crudely fitted British Trix couplings were replaced with Bachmann 36-026 couplings which spring fitted into position on the spigots originally for Tri-ang Mk3 tension lock couplings, Hymek was finally ready for layout testing in earnest.

On test I was not sure whether the Hymek was suffering from wheel slip on the 1:48 grade of my mainline circuit (folded figure of 8) with the test train of 6 re-wheeled British Trix coaches and two brake vans (Dublo & Wrenn) used for coupling conversions.

Running light engine the speed setting CVs were adjusted for a top speed of 70mph on step 28, this was timed at 90 seconds, repeated with the test train attached, same timing! The BEMF feature of the decoder working well with this motor.

So for my layout the extra weight was spot on, traction good, slow speed crawl was smooth, shunting quality even across pointwork, remember that DCC ready diesel locos are often very heavy, generally have all wheel pickup and drive. Vintage locos need to be guided to this.

Summary

A straightforward DCC conversion even with the additional work of increasing the number of wheels to collect power and additional weight to increase traction and improve power collection. The result is a smooth and strong vintage Hymek that will easily outlive a certain current DCC ready model.


Discussion always

Jim

Return to Index

 

Thanks Chris.

If you can, why not write them up and post them on here, admittedly it takes longer to do the conversion, but I am sure there are other modellers who would be interested.

My postings are just UK outline.

Jim