Hornby Railroad TTS class 31 modifications

Recently I bought one of these locos to see what sound was like on a small home layout of the shunting plank type. With an original style body using headcode discs finished in the plain green livery and sold at a bargain price for a sound fitted loco it seemed too good to resist.

I thought a few posts on how I changed it a bit here and there might be of help and use to anyone else wanting to do similar things, the basic idea being as usual to do this at minimal cost.

The model is fairly accurate being based around the exLima mouldings - there are some issues - but cannot represent the original 20 locos as built because the engine room doors have the grills fitted to later batches which were retro-fitted when they were re-engined. So for an early as-built version a number from the later batch ones also without headcode boxes needs to be chosen of which D5551 is one.

Unfortunately the TTS sound doesn't match up to the body for those that will know the difference (which I wouldn't), being of the later EE engines rather than the original Mirrlees and needing the exhaust ports at 90 degrees to those on the model. Since the loco livery represents a Mirrlees engined class 30 I have chosen to leave them alone.

I started by stripping the loco down and converting it to P4 as until this proved possible any other work wouldn't be undertaken. One aspect not mentioned so far is that compared to earlier models of class 31's this is quite accurate in respect of the bogie wheel arrangement, with the middle carry wheels being smaller than the outer ones, 12.5mm & 14.5mm respectively. Some past models have either had all the wheels the same size, or with some motor bogies no real carry wheels at all, just representations cast onto the bogie side frames.

Although this is an exLima loco in general respects to both the body and chassis mouldings, the newer design of Hornby Railroad motor bogie is now used instead of the older Lima pancake type, with the metal weights fitted into the fuel tank area of the plastic chassis to provide some weight to the model and aid traction. Two of the power bogie driving wheels - one on each axle - are also fitted with traction tyres. Electrical pickup is to all wheels on both bogies, powered and non-powered, even those with traction tyres.

Both bogies plug into the chassis and pivot on these plugs. They cannot be removed completely without un-soldering the wires to the pickups and motor. However, the wheels can be taken out by removing the keeper plate on the non-driven bogie, and the combined side-frames/keeper plate on the motor one. Both clip into place but neither remove particularly easily, the motor one having clips on the insides which are difficult to access, and the non-driven one moulded wedges on the inside ends which make it a very tight fit. I nearly gave up in despair at one stage trying to remove it and trimmed these wedges back with a scalpel for easier fitting and removal in future times.

My first thoughts were to simply replace the wheels with standard P4 coach and wagon types of 3'7" and 3'1" size. However, I then discovered that the wheels use 2.5mm diameter axles rather than the normal 2mm, with one wheel being all-metal, the other having a centre plastic insulating bush, so it was a case of machining the wheels to suit P4 track as I normally do, using the little lathe I have, and bearing in mind the use of traction tyres.

It did proved possible, but with one slight problem. The Hornby wheels have narrow but very deep flanges - about 1.1mm - and I reduced this to the standard 0.5mm depth I use. However, I had not allowed for the traction tyres, which tend to sit above the tread level in order to grip the rail. In practice this meant that at times the loco derailed, the wheels being lifted above the flange depth. Oh dear.

The traction tyres were thus ditched and rings of flat brass made which sat into the tyre grove. These were subsequently soldered into the wheel, the treads cleaned up, and all is now okay. Replacement wheels without traction tyres for the non-driven bogie are available as spares and getting a set and replacing the traction tyre wheels, these being the same as the powered ones save for the lack of gears, may be an option for anyone wanting to rid themselves of the traction tyre wheels whatever gauge they use.

You will see from the two shots of the wheels back in the non-powered bogie that there is nothing fancy about the construction, the axles just running in the plastic mouldings, no bearings etc. The PB current collectors bend easily to press on the wheel backs and pick up power and it all works fine.

This applies to the powered bogie as well. The motor is very powerful but with the rather low 16-1 gearing slow speed performance isn't perhaps all it could be, especially for a shunting plank, but you can't always have everything can you ?

Having got it running on the layout the fun could begin......

Izzy