Hornby M7 buffer locking

[John CutlerParticipant]

I have just about finished relaying a shunting yard.
This includes an a curved B6 turnout leading into an A5 through a reverse curve (effectively a kinked crossover). The curved B6 has previously given me no end of narrow-to-gauge problems.

A Hornby M7 negotiates this crossover OK. But when pushing a wagon in reverse the buffers invariably lock. Pushing frontwards, the buffers just about survive locking.
Surprisingly I have no problem with buffer locking on a loose-heeled 1in5 turnout!

My initial reaction was to try and fit a centring (14 gauge guitar) spring to enable the rear bogie to guide the chassis through a curve. I fitted a short handrail knob to the centre of the bogie (towards the buffer beam) and 2 long knobs drilled into the mazak ashpan. This spring position precludes the fitting of the plastic Hornby brake-pull. Unfortunately 2 issues arose. Firstly the long (AG) knobs are not long enough to give a horizontal spring run; they need to be around 4mm long. In an inclined position the spring forces the rear bogie wheel down and the front one up. 4mm knobs under the ashpan will be visually obtrusive and I doubt they are obtainable anyway. I do not believe that epoxying brackets to the mazak to carry the spring would last long and again they will be obtrusive. Secondly the spring had a tendency to lever (ping!) the bottom cover of the bogie off, allowing the pickups to stray!

I cannot fathom how to fit a centring device elsewhere.
I did look at reducing the bogie side-play but the M7 needs all its existing side-play to get through the reverse curve. The problem is centring the bogie, not side-play.

Has anyone managed to resolve this issue without resorting to a new bogie build?

The solutions I see otherwise are:
1. Increase the size of the rear buffer heads;
2. Change from Alex Jacksons to a coupling with an anti-buffer-lock (Iain Rice’s Imprecise?);
3. Ban the M7 from shunting the yard;
4. Rebuild the crossover (again; Ugh!) to a gentler reverse curve. I would first try replacing the A5 with another 1in5 loose-heeled turnout.

Any thoughts are welcome!

[Paul WillisParticipant]

John,

I would choose #3.

All of the others seem to be a disproportionate amount of work or are unprototypical.

And would the prototype have been able to navigate that combination in real life anyway? Perhaps better to build a little 0-4-0 to shunt, and add some more operational interest

[Dai DaviesParticipant]

@Paul Willis said:
John,

I would choose #3.

All of the others seem to be a disproportionate amount of work or are unprototypical.

And would the prototype have been able to navigate that combination in real life anyway? Perhaps better to build a little 0-4-0 to shunt, and add some more operational interest   

I have only one thought on this, and that is to agree wholeheartedly with this post. Why make life difficult? Perhaps a B4, USA tank, or whatever?

[Nick RidgwayParticipant]

B&6 A&5 does not make a crossover suitable for an M7, or anything other than an 0-4-0T, frankly.

At the ARPS Permanent Way seminar at Armley Mills in Leeds in 1990, Peter Olver, part of HM Railways Inspectorate at that time, recommended that a double line crossover be constructed with crossings of no lower number than 10 and absolutely no lower number than 8 for passenger lines in 12in scale.

A heritage railway in England constructed a crossover in 12in scale using crossings of 6 1/2 angle. I’ve travelled over it, and it came close to seeing the wrenching of corridor connections off the ends of Mk.1 coaches, even with buckeye couplers. This crossover had been replaced since, probably in response to the above recommendation.

Peco OO/HO large radius points have a crossing angle of about 1 in 5 1/2. It did not prove possible to achieve the propelling of Mk.1 coaches through a crossover built with them without buffer locking.

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