Rapido USATC S160 2-8-0

[Horsetan]

Two years in the planning, Rapido have just delivered this.

The S160 has never been mass-produced in 4mm scale before (although Roco did make a very good one in HO some years ago), and I've only ever seen two scratchbuilt efforts - one in OO, and the other in EM.

There's at least eight different livery variants available, and Rails of Sheffield have plenty of stock starting at a not too terrible £230 (more if you want it in DCC with sound).

At a glance, it looks as though it might be possible to convert it to P4 - axles appear to be 2mm diameter throughout (so longer replacements will be needed), and wheels look as though they will tolerate a session on a lathe, with most material being taken off the back to thin the flanges and maybe a light skim off the tyre face.

[Mol_PMB]

Will you have to move the cylinders out too, with the re-gauge? 

I'd be interested to see some photos of how you go about the conversion of something like this.

[Horsetan]

10 minutes ago, Mol_PMB said:

Will you have to move the cylinders out too, with the re-gauge? 

No. The cylinders appear to be exactly in the right place. What Rapido have done is to insert a thick washer/bush between the coupling and connecting rods in order to fill in the difference in gauge.

Removing the bush allows the coupling rods to move outwards when P4 wheelsets are inserted; connecting rods and return cranks don't need moving out, as they're already in the correct alignment.

[Horsetan]

On 25/7/2026 at 6:35 PM, Mol_PMB said:

...I'd be interested to see some photos of how you go about the conversion of something like this.

It's turning out to be a bit more complicated, which I would expect from Rapido, after reading the exploded diagrams.

The locomotive wheels are all mounted on shouldered axles and are insulated both sides using plastic bushes - similar to the Bachmann spec, and also IRM diesels so far. Shouldered axles have some advantages in that they are good at preserving the back-to-back measurement - once you hit the stop, that's it.

This means having P4 shouldered axles specially made. Possibly Ultrascale can do this, as they already make them for their GWR 44xx driving wheels, albeit a ⅛" dia. axle turned down to 2.5mm dia. at the ends. Rapido's are a different diameter on both counts.

I also must measure the overall width of the driving wheels in particular and see if it is practical to have metal skimmed off the back to thin the flanges.

The tender wheels are very familiar if you have encountered IRM coach bogie wheels - disc wheels mounted on a 1.5mm stub axle, and kept to gauge by a central insulating tube. There are ways of moving the wheels out with press tools.

[Mike 84C]

Looking at those exploded diagrams, they should be stamped with some sort of warning, " interfere with this model at your peril".

[Horsetan]

2 hours ago, Mike 84C said:

Looking at those exploded diagrams, they should be stamped with some sort of warning, " interfere with this model at your peril".

That's surely the whole point.

Rapido began by making models that were practically impossible to convert to P4 - see the 16xx pannier they produced for Model Rail magazine. A real nightmare to convert. When I saw the trouble a fellow Scalefour member had with it, I acquired the old Sutherland/NuCast 16xx kit and the Justin Newitt-designed chassis instead.

Edited July 28 by Horsetan

[Horsetan]

I'm after opening up the chassis to have a look, and can confirm the following:

Driving axles: 2mm diameter - all axles have a serrated central section intended for gear wheels, but only the rear driven axle makes use of this.

All axles are supported by sintered square bearings, similar to those seen on the Hornby 08 shunter. 

Overall wheel width: 2.8mm. There is scope to skim off the rear, which would thin the flanges, but I suspect this will only get you to 2.3mm wide at best - good for EM, but no better.

I wonder what the spares situation is? Would it be possible to buy direct from Rapido a set of 8 new drivers and insulating bushes, turn off the tyres on a lathe, and then press the bare wheel centres into new P4 tyres?

[Galteemore]

Looks like plunger pick ups too ….do those have enough spring in them to cover P4 width?

[Horsetan]

8 hours ago, Galteemore said:

Looks like plunger pick ups too ….do those have enough spring in them to cover P4 width?

Yes, they are. I haven't pulled the wheelsets out, but I would hope that the springs behind them can be extended.

[Horsetan]

In order not to ruin the model prematurely, I have sent an enquiry to Rapido to ask if they have any spare wheelsets, bushes and axles available to buy. I think it may be easier to work with these away from the model first.

In the event of Rapido's wheels being available, there is a possibility I can have these sent to Ultrascale to have the OO tyres turned off, and the centres pressed into Ultrascale's own bespoke P4 tyres (19mm would be the outer diameter, with a preferred overall width of 1.9mm), and then commission longer shouldered axles.

[Horsetan]

Update: Rapido have been quick to reply to say that they will not sell spare parts (they only keep those for warranty claims), so there goes that idea.

To be fair, I was expecting this, so it looks like the existing wheelsets will have to be sacrificed for any new tyres.

Edited Tuesday at 13:49 by Horsetan

[Mayner]

Interesting the Rapido parts diagram reminded me of another loco manufactured by Chines factory almost 20 years earlier.

                                             

While there were issues some quality issues (mechanical) with the first batch of Bachmann locos, durability of injection moulded pony & tender trucks became a significant problem. Interestingly the loco I bough second hand almost 10 years ago is still running reasonably well approx 18-20 years since manufacture.

Edited yesterday at 10:32 by Mayner