Bachmann Class 205 Thumper DEMU

[James Walters]

I have just placed an order for a Bachmann Thumper DEMU which will of course require conversion to P4.
Has anyone any experience of these? I don't have the unit yet, but am hoping to be as forewarned and forearmed as possible for the conversion work.
Any advice would be much appreciated.

Thank you and best wishes,
James

[ChrisMitchell]

Hi James

It is not something I have dine, but maybe that the drive system is similar to the various Bachmann DMUs in which case the Branchlines conversion set may suit.

There is also this thread about conversion of Bachmann split axle bogies that may be relevant

viewtopic.php?f=22&t=6817&sid=bab34fbfa638e22b8440425a84e5350d#p73046

Regards, Chris

[Philip Hall]

I have one of these to do, and the mechanism is similar (identical?) to the various Bachmann EMUs. I have obtained some of the replacement bogie stretchers for the EMUs that were available many years ago to convert the trailing bogies, but I'm not sure that those are still available. As I recall the bogies are too narrow for P4 wheels as they come, but since I now realise that slightly narrow P4 wheelsets (say 1.8mm) will run perfectly, it may well be that with some machining I will not have to do the widening, unless cosmetically they are too narrow..

One other problem (which yours may not have) is that the leading end of the power car is a touch too high and the body does not sit level. This was obvious even on some review samples, and it didn't get spotted but was obvious in photographs. I understand the cause was flash on the top of the power bogie casting or the lower edge of the mounting, but I have yet to investigate. On mine I also want to replicate the inter-vehicle buckeye and pullman rubbing plate so that the plates actually touch. Maybe that's making life difficult for myself.

Philip

[James Walters]

Thank you both for your helpful replies

Best,
James

[bécasse]

On mine I also want to replicate the inter-vehicle buckeye and pullman rubbing plate so that the plates actually touch. Maybe that's making life difficult for myself.

The inter vehicle buckeye/rubbing plate coupling was a distinctive feature of these units (cf comparable electric units which had single buffer/link couplings) and is well worth replicating. My inclination would be to make up the pair of rubbing plates and buckeyes as a single fixed unit articulated to each of the carriages - perhaps one with a bolt and one with a simple pin.

[Philip Hall]

Thank you David, that's an interesting idea. I had it in mind to spring each rubbing plate and have working (possibly not automatic) buckeyes in the buffer beams. I am fortunate to have a minimum of 4'6" radius curves so buffer to buffer contact etc is not difficult.

Philip

[davebradwell]

Chris Pendlenton covered Pullman gangways comprehensively in MRJ200. Would suggest you look at the "Wakefield" type which is part of the same piece. No point in re-inventing the wheel.

DaveB

[Philip Hall]

Thanks Dave, I'll have a look at that article. I'm thinking it will be a bit tricky since there is no gangway, just a rubbing plate. Plenty of time to think as it's a way down the 'to do' list.

Philip

[James Walters]

I have fitted my Hornby Maunsell stock with home-brew Buckeyes. The Buckeyes themselves are held onto NEM plugs using magnets so can be swiftly disconnected to split a rake, or separated conventionally, although the hinged jaw is fixed and they need to be split vertically - hence the magnetic element. I'm working on a MK2 version which will drop down when not in use. They provide very close coupling, and work well with Hornby's kinematic NEM system. I shall try something similar with the Bachmann Thumper, although I shall try to make improvements to the corridor connections as mentioned above.
Photo 1: Shows the buckeye fitted.
Photo 2: Shows a pair of the couplings and the magnet which connects to the NEM pin (not shown).
Photo 3: The coupling set-up and a big improvement on the tension lock gap. A thin piece of foam inserted in the gap seems to disguise this well as a quick interim fix.

Best,

James

[Philip Hall]

James, that's very neat. You have demonstrated an understanding, lost on some, of the fundamental requirement of the close coupling system in that the bar between vehicles has to be rigid and not flex in any way. Using ordinary Kadees, for example, will allow the connection to flex and the vehicles will not be pushed apart as much on sharp curves. Your fixed heads solve that one.

The German firm of Rowa was the first that I remember to offer this design and they were subsequently absorbed into Roco, who then used it on freight stock and engines as well as coaches. I guess it was the expiry of patents that led the likes of Hornby and Bachmann to take it on, but in doing so tinkered with the design that made it less effective, or at least Hornby did; I haven't seen a recent Bachmann example. The difference is that Rowa used a large round spring hooked between the bogie and the mount on the underframe to centre the coupling whereas Hornby use a small coil spring along the centre line. Roco/Rowa also did not have (at least in the early examples) the slot in the underframe which a hook on the top of the coupling engages in, ostensibly to take the pulling force; they used the large spring instead, so that vehicles were actually held in contact on the straight, and subtly began to open up on curves. The 'slot in the chassis and the weak spring' means that on curves with a heavy train the gap between carriages on a curve opens up a bit more.

I am using the Hornby couplings, with a slightly stiffened coil spring and with the coupling turned upside down (I remove the uncoupling pins), on my Maunsell stock along with the original Roco coupling heads (available from Howes I think) to bring vehicles together with the gangways touching as in the photo. A pipe either side can disguise the coupling bar. It is also possible to shorten the coupling pockets by approximately 1mm and use the supplied Hornby coupler heads, pinned into the pockets. The gangway cover plates are removed between vehicles and the coupling pockets adjusted so that the vehicles have to be slightly lifted to engage the couplings and they are held in ever-so-slight tension. There is no need for any gap on the straight. Your magnetic couplings will be able to achieve the same effect. With touching gangways it is possible to traverse 18" radius reverse curves, even in P4.

Philip

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