Finney 7 LNER A4

Discussion in 'Area 51' started by P A D, 1 October 2018.

  1. mickoo

    mickoo Western Thunderer

    Peter, can you show me the spacer issue that you had to adjust, I'm struggling to visualize where it might be.

    Your brake shaft error isn't yours, it's mine, the instructions are quite clear that the cranks go upward, my model goes downward and are now being rebuilt to correct this. At least you only did it once, I've done it wrong two out of the three builds :(

    Best MD
  2. Ian_C

    Ian_C Western Thunderer

    Different design approach to MOK but just as pleasurable to build.

    Certainly on the MOK 8F I don't think that Mr MOK completely understood the principles of compensation. With the arrangement here (and similar that on the 8F chassis) There is no effective cross compensation. You've effectively got a rigid 4 point chassis. Except on dead level track one pair of wheels will always be unloaded. Depending on the state of the track it'll be running over that may not be a problem in practice - but theoretically it ain't a good thing! And of course more of an issue in S7 than 0F. If it's any consolation the MOK 8F tender chassis makes a similar mistake with 3 axles, and I'll have to work out how to get around it when I get to that stage.

    Looking tidy though :thumbs:
  3. mickoo

    mickoo Western Thunderer

    As the rear dual beams are split left and right, I think that makes it three point does it not :confused:
  4. Steph Dale

    Steph Dale Western Thunderer

    It does, because the two rear beams aren't fixed to each other. The 'three points' are the pivot points of the beams; one at the front, two at the rear...

    simond likes this.
  5. mickoo

    mickoo Western Thunderer


    Thanks, I thought it did :cool:
  6. Ian_C

    Ian_C Western Thunderer

    No it doesn't. Hard to explain in words but...

    Think of each split beam as a single entity. All four of them are fixed to the chassis at a fixed point at a fixed height. If there's a twist in the track three of the pairs of wheels will contact the track, but the fourth pair can't accommodate because it's height relative the the chassis is fixed. Sure the beam can rotate but it can't move vertically out of the plane of the other three. The fourth pair of wheels cannot contact the track (although one wheel of the pair could but not carrying any tender weight, so effectively floating). As long as the vertical discrepancy is less than the flange depth of the wheel you'll probably be OK, otherwise re-railing gang called out.

    In a spirit of scientific curiosity I initially built the 8F chassis like this, just to check- it doesn't work! You're at the stage where you can wedge a little something under one wheel and see what happens.
  7. Steph Dale

    Steph Dale Western Thunderer


    The MOK 8F chassis has four beams, I think.

    This tender chassis has only three.

    The 'points' in each case are the pivots of the beams.

    So it's three point compensated. ;)

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  8. P A D

    P A D Western Thunderer

    Thanks for the comments on the merits (or lack of) of the compensation on the A4 tender. Applying engineering principles to models in this scale is "over engineering" in my view. I know I'm in the minority on this and a bit of a ludite,
    but it's only kit building.

    Suffice to say that when I ran my Finney A3 on the test track at the Doncaster show, the tender ran faultlessly on track that is very poor. I don't know whether the compensation is 3 point or not, but it works.

    Mick ,
    The error with the brake shaft was entirely mine. I had not noticed the error on yours when I did it . In fact I had the A3 tender on the shelf in front of me to refer to as well, but still got it wrong! :headbang:

    I'll take a photo to show you the issue with the rear brake hangers fouling the spacer and post it later.

  9. mickoo

    mickoo Western Thunderer

    You're not alone, I'm no fan of compensation beams, especially in engines when they get in the way of authentic stays and cross members or those items are compromised.

    The W1 is independently sprung or rigid, the B1 is independently sprung, rigid or compensation beams, but the beam system has alternative stays and items that were required to be compromised for that system. In short, accurate frames for springing or rigid, compromised frames for a compensation set up; the reasoning being, that if you're prepared to put great big fictional beams in there, then cut outs and mis-shaped stays are the least of your worries.

    It is a lonely path we tread, but I respect those that like it, hence it's offering in the B1, sadly the W1 was too far advanced in the design to retro fit.

    However, like you, I found the Finney7 tender set up pleasingly simple and fully functional and for those reasons have to give it 100% for functionality and effectiveness.

    If people spent half the time they do on suspensions/compensation beams/springing on their trackwork, then they wouldn't have to do the former ;)
  10. P A D

    P A D Western Thunderer

    The age old conflict between the CME's and Civil Engineer's departments!

    CE: "Your loco doesn't ride very well. Suspension's not up to much".

    CME: " I agree, it can't cope with your lousy track". :D

  11. Steph Dale

    Steph Dale Western Thunderer

    That depends greatly on the prototype; most of the stuff I'm working on can safely have both full frame and stay detail and compensation, should the builder wish it... :D

    To add to that a little, I tend to use compensation mainly on four-coupled locos where it helps greatly with haulage and pick-up - certainly as an 'out of the box' solution. In terms of other approaches, the mass of 7mm scale allows you get away with a great deal; especially in Finescale. As you both point out, that can make life a deal simpler.

    3 LINK likes this.
  12. mickoo

    mickoo Western Thunderer

    Ahh, yes, those quaint antiquated pieces of engineering south of the Thames ;)

    Anyway, it has it's place, is a tried and proved system, whether it's used is down to personal choice.

    Peter, fire away with that photo, I think I know where you mean (though I don't recall it being an issue here) but would like to make sure, and if necessary, make a correction in future instructions.

  13. P A D

    P A D Western Thunderer

    Hi Mick,
    I marked up where the spacer touches the rear brake hangers. It's where the rear part of the etch folds down (inner buffer beam) and then in between the frames (spacer).

    Here before folding, is where the hangers touch.

    I'll take a better photo when I can. Maybe, I've got something wrong, but I can't see where, as both assemblies are so simple.
    Last edited: 6 October 2018
  14. simond

    simond Western Thunderer


    I’m sure your tender will run fine, and long, without doubling the rocking beams, so I wouldn’t worry about it.

    That said, if you find it’s running a bit high (it looks like it could be, comparing the Slaters wheel screws with the holes in the outside frames), you could add the doublers and then use a thin file through the frame slots to align the edges, and shorten them to the correct ride height, two birds with a single stone!

    I completely concur that 4 axles can be 3-point compensated with a single central rocking beam supporting one pair of axles, and two independent ones close to the frames for the other pair. There are some kits which provide evidence that the designer does not understand the principle, by providing, for example a pair of independent rocking beams, and a fixed axle on an 0-6-0.

  15. P A D

    P A D Western Thunderer

    Hi Simon,
    Having bought my Finney A3 off eBay, it came with a full set of Slaters wheels, all the standard type with 3/16 axles. I decided these could be utilised, in full knowledge that on the tender, using 3/16 axles instead of the Finney type with 5/32 axles, would increase the ride height. So we are talking 1/64 inch or about 0.4 mm.

    Here is the A3 with its tender. The ride height must be "too high", but I doubt that anyone not having read the thread would know. Yes I know, but I'm a Luddite (correct spelling this time) and don't care. I preferred not to fork out for another set of wheels, that have extended axles that need cutting, and are push fit.

    Again, the Luddite in me prefers the tried and tested square axle ends with screw, that can be fitted and removed at will.

    The ride height therefore must be high on the A4 corridor tender, but I won't be trying to lower it. I would like to double the thickness of the beams and next time (on the W1, if/when I get one) I will do it in the flat. Your suggstion is of course do-able and thanks for that. However, I don't know what impact getting one slightly different to the others would have, so I won't risk it.
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  16. mickoo

    mickoo Western Thunderer

    I wouldn't beat yourself up about the ride height, the real tender height varies quite a bit between empty and fully loaded if you look at the real engines in service.
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  17. simond

    simond Western Thunderer


    The joy of equalisation is that if you get it a little bit wrong on one axle, the others will all still touch the floor! (You do have to get it level though!)

    Mick’s right though, coal & water were heavy stuff, and the springs would reflect that. The tender would start a journey right down on its springs, rise gently as the water was used, and the coal was burnt, be pressed down again as they picked up from the troughs, but the coal load steadily got lighter even as the crew picked up water and used it.

    So, even with half a coal load, it might be low on water, and thus quite high on its springs. And it might have new wheels too...

    Tim Watson likes this.
  18. P A D

    P A D Western Thunderer

    Thanks Simon and Mick,
    My thoughts exactly.
    Out of interest, I must put the loco and tender buffers to buffers, just to see what the difference is.
  19. P A D

    P A D Western Thunderer

    Somebody asked how close the pull rods are to the wheels. Near as damn it 1.7 mm on both sides. The outside ones on the A3 tender are about 1.5 mm which is what I was trying to do on the A4 tender. Not sure how I got it wrong but it looks OK so I'm leaving them.

    Here's the slots I had to make in the rear spacer/ vacuum tank mount, to clear the rear brake hangers.
    Here's a view after adding the riveted strip to the top edge of the frames. It fits under the fold down tank brackets, then the smaller brackets on the strip are folder up and then the inserts are added and soldered up. The front and rear steps have now been fitted as has the vacuum tank.

    This shows the clearance needed for the rear brake hangers and also the rear buffer beam.

    Here are the frames screwed to the chassis. Some fettling of the cross members on the frames and top edges of the chassis have lowered the ride height.

    The nuts are only screwed on as they will be soldered to the upper face of the tender running plate. This shows a better view of the buffer beam and rear steps.

    And the drag beam and front steps.

    Here are the springs, shackles and axke boxes prepped up ready for fitting. I believe these have been remastered from the originals, as the axle boxes are much better than the ones on the A3.


    Here's one of the A4 tender boxes next to the A3 tender.

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  20. mickoo

    mickoo Western Thunderer

    Not remastered, all new after measuring up at York one weekend ;)

    I will amend the instructions showing the cut out to clear the brake rigging, I honestly don't recall doing this on my three, but after inspection it looks like I must have.

    3 LINK likes this.