GENERAL NOTE: The Sang Cheng locos as supplied suit the Gauge One Standard set of wheel standards. They are free running with excellent sprung axleboxes. The couplings are quite a loose fit on the pins which may contibute to their free movement and lack of binding.
COUPLING ROD PINS. The pins are threaded to M2. As supplied they are hex headed bolts threaded in from the outside, screwed down tight to the brass sleeves.
They can be replaced with M2 screws countersunk from behind the wheels for extra tightness, with a nut on the front if preferred.
NOTE: Where locos have short coupling rod pin throws, (such as the GWR Pannier tank) screwdriver assess to the back of the wheels is prevented by the axle boxes and original screws fitted from the outside may be best.
Where locos have longer coupling rod pin throws, (such as the Class 03 Deisel) screwdiver access is possible past the gearbox after fitting if necessary.
Use 10 mm countersunk screws for the 03, with the original pin sleeves.
AXLES. Sang Cheng wheels are not modelled particularly closely to the prototype as far as the hub height is concerned and the axles may need modifying or replacing.
Class 03 Deisel. The prototype wheels have the hub slightly short of the tyre rims, so the Original San Cheng axles can be used, but need to be shortened from 52.0 to 51.4 mm. The bearings are press fitted so rather than attempt to remove them to for shortening in the lathe, I file 0.3 mm off each end by hand without removing the bearings.
GWR 57xx Pannier tank. The original wheels lack the raised hubs of the prototype and axles are too short. I machined new axles from Stubs precision ground silver steel. This is tool steel and quite hard so use a smaller cut and a high enough speed (at least 1000 rpm.).
Sang Cheng axles are made with 4.5 mm dia (3/16" is o'k but needs to be skimmed to 4.5 to fit the drive pinion wheel). Dia through the wheel is 3.0 mm, the end sections are 2.95 mm dia.
HUB INSULATION. I bore the hubs to 4.5 mm dia. The Delrin bushes are made with an overall dia of 4.85 mm, and bored to 2.9 mm for press fitting to the Sang Cheng 3.0 mm axles.
TIGHT AXLEBOXES. Check for free vertical movement of the axles boxes in the slots in the sideframes - if they are tight it helps to
scrape away some of the paint at the edges of the sideframe cut-outs.
CURRENT COLLECTORS. These need to be extended to reach the wider b-b of scale wheels. Unsolder the wires and remove the collectors. Cut them in half. Be careful to remove any protruding solder
from the original
wire connections to prevent shorting to the frame. Make new holes though the plastic tube to reveal the brass collector body at its inner end using a 3.0 mm milling cutter. Make sleeves to rejoin
the tubes (eg from Delrin) 5.9 mm i/d, 7.9 mm o/d x 15 mm long, and inner spacing plugs (Delrin) 5.9 dia x 3 mm long. Insert one half back into the body from the inside with the sleeve
(containing the plug) on it, insert the other half through the side of the frame. At this stage the parts are loose and can be slid into position, then apply glue. Solder the wires to the brass
collector bodies through the new holes, further away from the metal frame.
PAINT. For 2-rail electric locos remember to leave the backs of the tyres unpainted for current collection.
AXLE SIDE PLAY. This can be reduced by fitting brass spacers between the wheels and the axleboxes on the outer axles. Eg. 5.0 mm round brass rod, bored to 3.0 mm dia x 2.0 mm long in addition to the
0.8 mm top hat rim at the base of the insulating bushes.
If fitting spacers to intermediate axles make sure that they remain with enough side play for model curved track.
Class 03 FLY CRANKS. Insulate the fly crank rod pins just in case a coupling rod should happen to touch a live wheel rim and causing an electrical short.
Keep the original screws but replace the brass sleeve with plastic (Delrin), with a top hat rim one end and an insulating washer on the other. The length through the rod can be reduced to 2.0 mm
to reduce the amount of side play and improve the clearance of the bolt heads.
QUARTERING: the Sang Cheng loco comes with the coupling rods quartered with the left side leading. The fly cranks have to be requartered to match the wheels if they
are mounted with the right side leading.
LOCOS WITH OUTSIDE CYLINDERS: in these locos you will need to insert insulating bushes into the wheels, and thread them for the coupling rod pins.
Revised 9 June 2023 following conversion of a GWR 57xx and some BR class 03 Diesels.