Rebuild Merchant Navy Class, Cilinder layout?

[RJdeVries]

Hi Everyone,

 

I've recently bought a 2nd hand model here in the Netherlands of a

Hornby rebuild Merchant Navy class, the model is pretty nice and I

am preparing it to use it on my layout, prior it will need a sound chip

fitted, ESU loksound 5 with a Hall sensor to controll the chuffs, for that

realistic chuffing sound.

 

Now, the Hornby model has the wheels set to an offset of 90 degrees and

that doesn't seem right for a 3 cilinder, should this not be 120 degrees?

 

Or is there something else up with the real 1;1 locomotive that I am not

aware of, I did search the internet and did sadly not really get an answer.

 

 

Hopefully someone can help, that would be great!

 

Regards,

 

Robbert Jan.

[Mallard60022]

Go online and look at the info about Walschaerts Valve Gear...….http://en.wikipedia.org/wiki/Walschaerts_valve_gear

There you should find the diagram(s) and also the position for the Eccentric Crank (& Rod) that 'leans back' at bottom dead centre, rather than the conventional 'leans forward'. It is possible to adjust the position of the Crank IIRC.

Hope this helps.

Phil

This diagram does not help much as the top shot shows the rods in mid position but you should be able to see how the crank would be leaning back at bottom dead centre?

Edited September 15, 2019 by Mallard60022

[Right Away]

The cranks on the prototype are 120° apart. However, whether Hornby replicate this with accuracy on their outside cranks with respect to the middle engine is another thing. 

 

 

[RJdeVries]

I've also been concluding that there is a 120° offset between

the cranks, however this is probably not a great offset for a

model, rather using a steady 90° offset for ease of use.

 

I will try to make it work, the model was cheap so no harm

in a bit of experimentation, I did already place 6 magnets

behind one wheel to trigger the Hall sensor, spaced 60°

apart.

 

Thanks for the usefull help, sorted!

 

Regards,

 

Robbert Jan.

[Mike Buckner]

Well, I suppose you will usually only be looking at one side of the loco at a time...

[Michael Edge]

Rebuilt Bulleid Pacific's have outside admission, not the usual inside admission illustrated above.

[RJdeVries]

Mike Buckner, 

 

That is indeed correct and it would normally not bother me at all, but since the loco will have an

accurate output of the chuffs due to a sensor and 6 magnets (spaced 60deg apart) viewing the

loco from one side will be allright, the other, not so much since it will be slightly off.

 

I know, what a hassle, thats true and I will not lie that it is a bit of a strange habit of mine, like 

seeing a pavement with 2 oddly placed pavers, it sometimes gets to you

 

 

Regards,

 

Robbert Jan.

[RLWP]

Gresley pacifics have an irregular crank spacing, something like 120/115/125 degrees*

 

I wouldn't change the loco you have, chances are it will run badly if you do. At 120 degrees you'll exaggerate the free play in the chassis and connecting rods, making it more likely one wheel will get itself out of sync locking up the chassis

 

Richard

*There's a good reason for this

[34theletterbetweenB&D]

 

12 hours ago, RJdeVries said:

I've also been concluding that there is a 120° offset between

the cranks, however this is probably not a great offset for a

model, rather using a steady 90° offset for ease of use...

None of the OO manufacturers have ever tried the correct 120° crank offset for three cylinder simple locomotive models, even though it is the most common multicylinder arrangement on the UK's railways, and applies to the majority of the ever popular pacific locomotive classes. It will work in model form, but as you suspect and Richard mentions, does demand significantly greater precision than the 90° crank setting. Small chance of any OO manufacturer inclined to take this risk.

[Michael Edge]

It will work perfectly well at 120 (I've tried it before out of curiosity) but you'll never see the difference, you can't see both sides at once. My comment was really about which way the return crank should lean, in this case backwards fro outside admission valves.

[PhilH]

8 hours ago, RLWP said:

Gresley pacifics have an irregular crank spacing, something like 120/115/125 degrees*

 

 

 

As do Bulleid pacifics, 120/114/126 deg.

 

Edit. this was discussed here which might or might not be of interest to the op.

 

Edited September 16, 2019 by PhilH

[RLWP]

55 minutes ago, PhilH said:

 

As do Bulleid pacifics, 120/114/126 deg.

 

Master and pupil

 

Richard

[DCB]

I suspect at least one preserved Bulleid has 120 crank spacing as I have heard a noticeably lop sided beat as it pulls at slow speed obviously with separate valve gears it doesn't actually matter the valves will still be in phase with the pistons..

Gresley / Holcroft 2:1 gear can only work at 120 degrees between power strokes, that is why Gresleys have to have the offset crank pins to allow for the angle of the inside cylinder vis a vis the outside ones,  Properly set up it gives a beautifully even beat, see Sir Nigel herself on the NYMR.   Such a shame the old time fitters never did seem to get the hang valve setting until Cook of the GWR turned up on the ER and made the Gresleys run like, well like GWR locos.

[Dunsignalling]

On ‎16‎/‎09‎/‎2019 at 16:37, Michael Edge said:

It will work perfectly well at 120 (I've tried it before out of curiosity) but you'll never see the difference, you can't see both sides at once. My comment was really about which way the return crank should lean, in this case backwards fro outside admission valves.

On a finescale chassis, with its inherently tighter clearances, It should indeed work.

 

On a typical r-t-r mech incorporating a load of slop to help it cope with dodgy r-t-r track, I'd expect the thing to tie itself in knots fairly quickly.

 

John

 

 

Edited September 18, 2019 by Dunsignalling

[Mallard60022]

On ‎15‎/‎09‎/‎2019 at 23:13, Michael Edge said:

Rebuilt Bulleid Pacific's have outside admission, not the usual inside admission illustrated above.

Mike, the top diagram shows the outside admission position but not with bottom dead centre (BDC) to illustrate the simple crank lean that you need to do on a model loco such as the Bulleid Modified Pacific. As Mr Wright would suggest, just loosen the nut and tweak the crank to lean back a tad at BDC; just needs to look that way but hardly noticeable really unless you stare at it from close range.

The actual * of angle for this isn't critical as to be the angles mentioned above.

ATB

Phil

[RLWP]

3 hours ago, DavidCBroad said:

 Such a shame the old time fitters never did seem to get the hang valve setting until Cook of the GWR turned up on the ER and made the Gresleys run like, well like GWR locos.

 

Which no doubt Churchward learnt on his visit to Crewe works (his signature is in the visitors book)

 

Or some other similar shite

 

Richard

[DCB]

1 hour ago, RLWP said:

 

Which no doubt Churchward learnt on his visit to Crewe works (his signature is in the visitors book)

 

Or some other similar shite

 

Richard

Wrong CME  Collett brought accurate measurements to Swindon following his apprenticeship and background with I believe Maudslays and sons who were not railway engineers but precision engineers.  K.J.Cook's book Swindon Steam is a good read, I think it covers his work on the ER briefly, as is "Top Shed" where curing the A3/ A4 heating woes with GWR inspired big end bearings is mentioned, as is the change from single to Kylchap exhausts.  Pre Cook 2 X A4s did the London - Edinburgh run amid considerable and worry the rest did relays, KX - Grantham   Grantham-  Newwcastle  Newcastle - Edinburgh etc.  Post Cook they were doing London - Edinburgh - London in a day.

 

I expect Crewe wanted to pick Churchward's brains over Walchaerts valve gear as he built around 130 ish locos with this gear before "Sir Gilbert Claughton" wheezed and clanked forth from the Hallowed portals.  I expect he told them it was marvellous  and didn't mention 95 of his were tiny railmotor power units.