Wright writes.....

[Jol Wilkinson]

Care to work out if I got this right Tony?

(Joy valve gear on an LNWR Teutonic).

 

[Compound2632]

24 minutes ago, Jol Wilkinson said:

 A Joy to Behold!

[t-b-g]

53 minutes ago, Jol Wilkinson said:

Care to work out if I got this right Tony?

(Joy valve gear on an LNWR Teutonic).

 

 

After battling with some inside Joy motion for a 7mm LNWR Prince of Wales, Vincent Worthington came to the firm conclusion that it should be called "No Joy" valve gear.

[Ian Rathbone]

Further to the valve gear discussion, as well as the rebuilt Bulleid Pacifics Maunsell’s N, N1, U, U1, W & Z  classes all had ‘backward leaning’ return cranks. These are the only examples of British locomotives that I know of. The other difference with the Bulleids is that the radius rod attaches to the combination lever below the valve rod.

 

Of course all Tony’s 3 cylinder engines should have their opposing cranks set at 120 deg rather than 90, but I won’t go there.

 

Ian R

[LaScala]

25 minutes ago, Ian Rathbone said:

Further to the valve gear discussion, as well as the rebuilt Bulleid Pacifics Maunsell’s N, N1, U, U1, W & Z  classes all had ‘backward leaning’ return cranks. These are the only examples of British locomotives that I know of. The other difference with the Bulleids is that the radius rod attaches to the combination lever below the valve rod.

 

Of course all Tony’s 3 cylinder engines should have their opposing cranks set at 120 deg rather than 90, but I won’t go there.

 

Ian R

We all know Tony dislikes DCC, or Dumb Crank Connections

[Tony Wright]

44 minutes ago, Ian Rathbone said:

Further to the valve gear discussion, as well as the rebuilt Bulleid Pacifics Maunsell’s N, N1, U, U1, W & Z  classes all had ‘backward leaning’ return cranks. These are the only examples of British locomotives that I know of. The other difference with the Bulleids is that the radius rod attaches to the combination lever below the valve rod.

 

Of course all Tony’s 3 cylinder engines should have their opposing cranks set at 120 deg rather than 90, but I won’t go there.

 

Ian R

Good evening Ian,

 

I will go there!

 

The LNER three cylinder Pacifics should have their cranks set at 180 degrees, as you so rightly state. However, since no modeller I know is a chameleon, then the fact is academic. Another thing, if, say, I used friction-fit drivers instead of Markits (which can only be set to 90 degrees, or 180! Yes, at one Missenden a guy had set his cranks to 180. It took me ages, and much in the way of bad language, before I figured out why his chassis didn't work!) and set them to 120 degrees, would the model actually work? 

 

Our electric steam-outline locos are essentially 'one-cylinder' machines, with only a single 'thrust'. A real three cylinder steam loco has six positions in a rotation where each crank is actually having pressure applied to it.

 

I could have got this completely wrong (having taught art hardly qualifies me as an 'engineer'), but I'm sure the rods would bind at some point in the rotation. 90 degrees gives the best turning moment, doesn't it? 

 

As for 'leaning-back' return cranks, didn't the LMS Garratts have them, and the Fowler 2-6-2Ts? 

 

Regards,

 

Tony. 

Edited January 3 by Tony Wright
to add something

[30368]

42 minutes ago, Ian Rathbone said:

Further to the valve gear discussion, as well as the rebuilt Bulleid Pacifics Maunsell’s N, N1, U, U1, W & Z  classes all had ‘backward leaning’ return cranks.

 

I would add the Maunsell re-builds of the LBSCR Baltic Tanks - the N15X 4-6-0 to this list.

 

Kind regards,

 

30368

[Nicktoix]

52 minutes ago, 30368 said:

 

I would add the Maunsell re-builds of the LBSCR Baltic Tanks - the N15X 4-6-0 to this list.

 

Kind regards,

 

30368

Also LSWR C14.

Generally trailing return cranks imply inside admission usually with slide valves. Piston valves are generally outside admission.

Nick

[St Enodoc]

9 hours ago, Tony Wright said:

The lean is wrong on this side of this Hornby rebuilt West Country.

Is there a general rule for the differences on locos with different cylinder arrangements (2/3/4 cylinders, slide/piston valves, inside/outside admission, different crank angles, etc.)?

Edited January 3 by St Enodoc
Read more posts!

[mozzer models]

On 09/08/2023 at 10:29, melmoth said:

 

 

IIRC, they went from Bettabitz to 247 Developments, but I don't think they were included in the sale when 247 Developments was sold on to Brian @247 Developments  . Obviously Brian will known better than I do.

were still with Errol when i tuck over I believe there now with Squiers

[Chuffer Davies]

2 hours ago, Tony Wright said:

Good evening Ian,

 

I will go there!

set them to 120 degrees, would the model actually work? 

 

 

Regards,

 

Tony. 

Hi Tony,

I can only surmise that if a prototype works with cranks offset at 120deg then in theory a model should also work with the same offset.  As yet I have not built a model of a three cylinder locomotive but if I ever do I’ll certainly give it a go. 
I wonder if anyone on WW already attempted to do this?
Frank

[lezz01]

57 minutes ago, St Enodoc said:

Is there a general rule for the differences on locos with different cylinder arrangements (2/3/4 cylinders, slide/piston valves, inside/outside admission, different crank angles, etc.)?

I only know about 2 and 3 cylinder and I'm not crash hot on the triples I only know about the MR compounds and not that much detail. With a two cylinder inside cylinder loco the cranks are set at 180deg to the crank pin and the right hand side is 90deg advanced to that on the left as seen from the cab. The valve timing is done with eccentrics and a radius arm on a Stephenson link motion. I don't know about other types of valve gear, I can just about sort out how Stephenson link motion works in my head I don't have a clue about Joy or other types. I've never really seen them working but I could probably sort it out if I saw them working for a while. One of the eccentrics in a pair has a lead but I'm not sure which one leads but I think it's the one on the right but I don't know why and if it's the same on the left hand side or if it's a rule that the outside leads or the right hand of each pair lead. On the compound the inside cylinder works at a different pressure to the outside two and I'm not sure which is the higher and I have no idea where the inside cylinders crank is set in relation to the outside two but the logical place would be at 135deg from the other two. Given that the outside cranks have the standard 90deg lead on the right hand side the midpoint would help balance the driven axle. That's all I've got I'm afraid.

Regards Lez.         

[ndeluck]

On 02/01/2024 at 15:32, LNER4479 said:

Easy enough, Tony (for a man of your calibre). Simply remove the return crank and big end of the conn. rod to expose the main crank pin. There's a couple of notches that engage with pips on the inside of the crank pin. With a piercing saw (suggested), carefully saw a new set of notches on the end of the main crank pin - if necessary, dress / deepen with suitable needle file.

 

I've not done it on an A1 per se but have now done quite a few LMS 4-6-0s and it's exactly the same procedure.

 

If the above is unclear, I'll strip one of mine down and take some photos.

I'm no Mr. Wright but would you mind demonstrating the disassembly of Bachmann cranks for those of us who have no experience with the modern chassis toolings? I've run into issues with a few of my own and am, rightly so, a bit nervous about how to approach!

[MarkC]

9 hours ago, Tony Wright said:

 

 

I could have got this completely wrong (having taught art hardly qualifies me as an 'engineer'), but I'm sure the rods would bind at some point in the rotation. 90 degrees gives the best turning moment, doesn't it? 

 

As I see it, setting the cranks on our models at 90 degrees (+/- a tiny amount if setting friction drivers by eye, of course...) means that it minimises the possiblity of the mechanism binding due to rod position, so yes, it's to do with turning moments. Remember that we're actually operating the rods/valve gear/piston rods in reverse; the wheels are driving these components, not the other way round. The 120 degree setting on a real 3-cylinder locomotive is to do with putting power down to the wheels in a more even manner than on a 2-cylinder loco.

 

Mark

[Tony Wright]

8 hours ago, Chuffer Davies said:

Hi Tony,

I can only surmise that if a prototype works with cranks offset at 120deg then in theory a model should also work with the same offset.  As yet I have not built a model of a three cylinder locomotive but if I ever do I’ll certainly give it a go. 
I wonder if anyone on WW already attempted to do this?
Frank

Good morning Frank,

 

But, as Mark C has pointed out, it's the crankpins on our models which are 'driving' the connecting rods; the opposite of the real thing.

 

As I mentioned in response to Ian Rathbone, during every rotation of a real three cylinder loco's wheels there would be six 'points of pressure' being exerted. This is not the case on an electrically-driven model, and I'm sure it would lead to the rods binding; though I've never tried it. As you have asked, has anyone?

 

Now, a question from a non-engineer. In a four cylinder loco, assuming the cranks are set to 90 degrees, are the two outside crankpins always set to 90 degrees from each other?

 

Regards,

 

Tony. 

Edited January 4 by Tony Wright
poor punctuation

[Bernard Lamb]

11 hours ago, Ian Rathbone said:

Further to the valve gear discussion, as well as the rebuilt Bulleid Pacifics Maunsell’s N, N1, U, U1, W & Z  classes all had ‘backward leaning’ return cranks. These are the only examples of British locomotives that I know of. The other difference with the Bulleids is that the radius rod attaches to the combination lever below the valve rod.

 

Of course all Tony’s 3 cylinder engines should have their opposing cranks set at 120 deg rather than 90, but I won’t go there.

 

Ian R

The American built S160s are an interesting mix in respect of this point, if I understand it correctly, mainly upper but one batch lower.

Bernard

[Northmoor]

8 hours ago, lezz01 said:

On the compound the inside cylinder works at a different pressure to the outside two and I'm not sure which is the higher

Whichever is the larger cylinder will be the lower pressure one, the larger bore compensating for the lower pressure to even out the force on the cranks.

[St Enodoc]

1 hour ago, Tony Wright said:

As I mentioned in response to Ian Rathbone, during every rotation of a real three cylinder loco's wheels there would be six 'points of pressure' being exerted. This is not the case on an electrically-driven model, and I'm sure it would lead to the rods binding; though I've never tried it. As you have asked, has anyone?

Assuming you mean just the coupling rods and not the whole valve gear, I think binding would only be a problem if the cranks were at 180 degrees but, like you, I've never tried.

 

1 hour ago, Tony Wright said:

In a four cylinder loco, assuming the cranks are set to 90 degrees, are the two outside crankpins always set to 90 degrees from each other?

That's a subset of what I was asking earlier.

Edited January 4 by St Enodoc

[t-b-g]

One of the reasons why Gresley liked the 3 cylinder designs rather than 2 is because the power was applied more evenly to the driving wheels. They got a "push" and a "pull" from the cylinders spaced evenly three times per revolution.

 

I recall being told that when it came to starting a heavy train, it was the best way to apply power evenly and smoothly and that the O2s were better at starting heavy freight trains than the O1s and O4s.

 

I have read of a modeller who set his cranks at 120 degrees with no adverse effects. As long as you have one rod that can pull or push the wheels around when the other is "dead centre" then you shouldn't have a problem.

 

I also record reading that 4 cylinder designs varied in that some had each cylinder set at 90 degrees and some had two pairs of cylinders acting together. As far as I know, all the outside cranks were set at 90 degrees, to reduce the additional hammer blow of two lots of coupling rods going round together.

[Michael Edge]

8 hours ago, Chuffer Davies said:

Hi Tony,

I can only surmise that if a prototype works with cranks offset at 120deg then in theory a model should also work with the same offset.  As yet I have not built a model of a three cylinder locomotive but if I ever do I’ll certainly give it a go. 
I wonder if anyone on WW already attempted to do this?
Frank

Yes, 120deg works perfectly, I've tried it a few times (mostly out of curiosity) - as Tony says, it's impossible to see it. Four cylinder locos normally have inside ones at 180deg. from the outside ones, giving four beats exactly as a two cylinder loco so they will have outside cranks at 90 deg. The best known exception is the SR Lord Nelson but one of these was modified to conventional with no discernible difference.

Incidentally inside cylinder locos sometimes have the cranks in line with the coupling rods, giving rise to much larger balance weights in the wheels, GW 56xx is an example of this.

[Michael Edge]

4 minutes ago, t-b-g said:

One of the reasons why Gresley liked the 3 cylinder designs rather than 2 is because the power was applied more evenly to the driving wheels. They got a "push" and a "pull" from the cylinders spaced evenly three times per revolution.

 

I recall being told that when it came to starting a heavy train, it was the best way to apply power evenly and smoothly and that the O2s were better at starting heavy freight trains than the O1s and O4s.

 

I have read of a modeller who set his cranks at 120 degrees with no adverse effects. As long as you have one rod that can pull or push the wheels around when the other is "dead centre" then you shouldn't have a problem.

 

I also record reading that 4 cylinder designs varied in that some had each cylinder set at 90 degrees and some had two pairs of cylinders acting together. As far as I know, all the outside cranks were set at 90 degrees, to reduce the additional hammer blow of two lots of coupling rods going round together.

Not just Gresley, this is the reason why the GCR 0-8-4T hump shunters had three cylinders.

[CF MRC]

About four years ago, I purchased a 3.5” gauge A3. After some mainly cosmetic work it became Hyperion. 

One aspect of the engine that eventually meant that I sold it on was that, like many live steamers, it had slide valves with outside admission, which meant that it had the radius rod below the valve spindle: once I realised this it niggled greatly. Its performance was also adequate, but I think it would have needed some fairly extensive work to make it sparkle. Many locos like that never get re-assembled once someone starts to fiddle. 
 

It was replaced by a 3.5” Maunsell King Arthur, which I am currently working on. This was 90% complete and has some exceedingly fine engineering in it. 

The engine has inside admission  piston valves with the correct valve gear layout. The cylinder cover sheets are not quite the correct shape at the  top by the running board: they should be flush and so are due for re-working. Might that account for some of the previous comments about the S15 cylinders?

I always set wheels in the relationship of the prototype: there is no reason not to in 2mm scale. 
 

Tim

Edited January 4 by CF MRC

[t-b-g]

37 minutes ago, Michael Edge said:

Not just Gresley, this is the reason why the GCR 0-8-4T hump shunters had three cylinders.

 

I should have had them as my first example being a GCR man!

 

The ones fitted with boosters must have been amongst a very small number of locos with 5 cylinders. I can think of the C9 NER Atlantic rebuilds and the P1s and not much else.

[Dunsignalling]

9 hours ago, lezz01 said:

I only know about 2 and 3 cylinder and I'm not crash hot on the triples I only know about the MR compounds and not that much detail. With a two cylinder inside cylinder loco the cranks are set at 180deg to the crank pin and the right hand side is 90deg advanced to that on the left as seen from the cab. The valve timing is done with eccentrics and a radius arm on a Stephenson link motion. I don't know about other types of valve gear, I can just about sort out how Stephenson link motion works in my head I don't have a clue about Joy or other types. I've never really seen them working but I could probably sort it out if I saw them working for a while. One of the eccentrics in a pair has a lead but I'm not sure which one leads but I think it's the one on the right but I don't know why and if it's the same on the left hand side or if it's a rule that the outside leads or the right hand of each pair lead. On the compound the inside cylinder works at a different pressure to the outside two and I'm not sure which is the higher and I have no idea where the inside cylinders crank is set in relation to the outside two but the logical place would be at 135deg from the other two. Given that the outside cranks have the standard 90deg lead on the right hand side the midpoint would help balance the driven axle. That's all I've got I'm afraid.

Regards Lez.         

 

ISTR reading in a volume of yore that prototype convention was for right-hand lead.

 

Apart from the SR Lord Nelsons, I think 4-cylinder crank settings were at 90-degree intervals, with each of the two outside cylinders aligning with, but on the opposite stroke, to one of the inside ones. 

 

Where it comes to 3-cylinder types, though, Tony is constrained in angular distribution by his preferred supplier of wheels and axles. 😉

 

John

 

 

Edited January 4 by Dunsignalling

[gr.king]

40 minutes ago, Michael Edge said:

Not just Gresley, this is the reason why the GCR 0-8-4T hump shunters had three cylinders.

Likewise, I assume, Raven's NER 4-8-0T hump shunters, his 4-6-2T mineral locos, and the T3/Q7 0-8-0s.

 

On the matter of crank positions, I was interested to read somewhere, possibly in a Tuplin book, that for an inside cylinder loco the orientation of the cranks for the outside rods was found to give least trouble with balance and stress if it matched the adjacent inside crank, in contrast to the instinctive approach of some engineers who had placed the outside cranks at 180 deg to the adjacent inside ones.