Binding Coupling Rods on CSB chassis for 4mm DJH Duchess

[gaf2u]

Hello

Haven't posted for a long time, but frustration is driving me to seek pointers or advice on this chassis.

 

I am building a 4mm DJH Duchess kit, and decided that I wanted to convert it to a continuous spring beam type per the CLAG protocol. This is my first attempt at this as all previous chassis have either been uncompensated, or done per the Sharman flexichassis 3-point principle. Used the CLAG excel calculator (there's no sketch for a Duchess chassis layout in the templates at present) to determine fulcrum positions, and the new High Level CSB jig to mark them onto the chassis.

Fitted High Level hornblocks (standard on two axles, and space savers on rearmost driven axle) which are a dream. Worked out fantastic, and chassis rolls really smoothly when wheeled up with no motion gear fitted- I'll do all future chassis this way I think.

 

I have now encountered a bit of a hurdle though. I split the coupling rods and reformed into two pairs for left and right sides, having laminated Gibson universal coupling rods to the rear of the DJH ones supplied. Fettled as required, fitted crankpin bushes, and got everything to roll nicely with coupling rods fitted. Inserted a North Yard 36:1 2-stage box (this seems to be the only one narrow enough to fit a DJH chassis with hornblocks) and powered up via a temporarily mounted Mashima motor.

 

Problem - runs perfect in one direction (reverse as it happens) and is very snatchy in the other. I put this down to the gearbox first, and fitted an internal bush to eliminate the considerable float in the drive / worm shaft, and lubricated everything well. No better! Removed coupling rods and the gearbox plus drive axle runs smoothly in both directions. Fettled crankpin bushes some more and got a slight improvement. Noticed one crankpin was slightly out of true, remedied this, and it improved a little more. It is still quite snatchy though in the forward direction, and seems to have a tight spot, despite the fact that the chassis rolls easily when the gearbox is removed.

 

Any ideas??? Is it time to make up a new set of coupling rods. I'm afraid to take any more out of the crankpin bushes in case they get too sloppy and lock up under power.

 

See images below. I've also included a piccie of a Gibson Crab I have nearly finished - lovely kit, and an old K's Jubilee that is in the works and has a Comet chassis fitted. There's quite a bit of Miliput filler on the body to try improve the finish for painting.

 

 

This is the left side of the chassis, with gearbox in place, and coupling rods in-situ.

 

 

The Crab - stalled now until I get enough together to merit a painting stint

 

 

The Jubilee, with Comet chassis and tender. Motion fitted temporarily, awaiting painting too!

[3 link]

Is there much side play ( 9 o clock to 3 o clock position ) between the blocks and the guides, sometimes this can cause a bind. It's quite hard sometimes in the smaller scales to find a happy medium, also the bushes do look a bit tight on the rods which looks nice but also do not leave much tolerance, so maybe a little bit of opening up of the holes on the rods with a broach might do the trick.

 

Martyn.

[John_Hughes]

Really you need no play at all between the blocks and the guides; they need to slide freely, but have no side-to-side movement at all. And I'd be leery of opening up the holes for the crankpins to give more than perhaps 3 or 4 thou of slop or perhaps a little more, though as everyone who's ever checked out a Hornby or Bachmann chassis will know, it's possible to get smooth running with a lot more slop than that!

 

If you're absolutely certain that the rods and the axle-spacings are precisely matched (I use the good old Percy jigs for this) and equally certain that the wheels are quartered exactly the same on each axle, then I'd be inclined to check the crankpins, which can be an unsuspected source of trouble. Are the all exactly perpendicular to the wheel-face? And exactly the same distance from the axle centre?

 

Easing out this sort of binding is a job that can take ages, working one step at a time, and more than once I've felt like throwing a recalcitrant chassis at the poor blameless cat! They always sort in the end, though!

[buffalo]

A six wheel chassis with split rods and driving on the rear axle does need some care to set up whatever springing or compensation method you use. From the way you describe what you have done, it seems to me that you are working backwards. By that I mean a better approach would be to start with the rods and use them to align the axleboxes and hornguides. The High Level parts are difficult to get to be too loose but do require accurate alignment. Building the chassis first then trying to get a set of rods to fit simply by opening up the crankpin holes will never give the best results.

 

Others with far more experience than me will hopefully be able to help you retrieve the situation.

 

Nick

[gaf2u]

Martyn, John,

Thanks for the replies.

 

I've checked the hornblocks, and to be honest there's little, if any, side-play in them. That was why I included the comment about the High Level blocks working a dream. They went together very well and the blocks slide nicely but not loosely in the guides. I've had awful bother with Gibson hornblocks previously, and had to dismantle a Fowler 2-6-2T chassis before, because the sideplay was such that everything locked up once the motor started turning.

 

I've run a broach through the crankpin bushes again since Martyn's reply, but I'm loathe to take too much out. They are already quite loose (couldn't put a measure on the clearance but it is readily evident to the eye).

 

Good advice on the crankpins - already found one this evening that wasn't perpendicular to the face of the wheel, and righted that. Hadn't thought of checking the radial measurement from hub centre to crankpin centre though - will look into that.

 

The wheels are Romfords, so I am assuming the quartering is good. Not sure if it possible to adjust it if required in any case.

 

Hornblock locations were marked using the High Level jig once the original bearing holes were reamed out sufficiently. I too have a set of Perseverence axle jigs and all seemed in order using these along with the DJH single piece coupling rods when soldering hornblock guides in place.

 

What I can't understand is why everything runs flawlessly in one direction, and is only problematic in the other opposite direction!

 

As you say John, one step at a time, but after a week of little improvement I am starting to despair a little. I've no cat to target with the piece if my temper gets upper hand, only two dogs, and I don't doubt that they'd think such a rash act could only be part of a new game, resulting in much tail-wagging, yelping and slobbering, which would only rub salt in my wounded pride.

 

Darren

[craigwelsh]

Is the problem still there if you turn the shaft on the gearbox by hand? Do you have a torque link on the gearbox? I'm just wondering if going forward the gearbox is pressing down on something upsetting the CSBs..

 

If it still rolls fine ok without the box in both directions its got to be something like the above i'd have thought?

[Paul Cram]

Is it possible to remove the rods from either the fronyt or rear wheels and test the wheels in pairs? This would then isolate the area where the chassis was binding. I have a similar problem with a J21 and have managed to isolate it asd the middle wheel on one side which needs to be eased but havent got around to that yet as pickups were also too tight.

[Horsetan]

....I've also included a piccie of a Gibson Crab I have nearly finished - lovely kit....

 

Slightly OT, but on your sample Gibson "Crab" kit, did you encounter a front footplate that overhung the buffer beam like a diving board, like I did?

[billbedford]

If you have a rolling chassis, ie you can take the worm out of the gearbox, The way to check for quartering error is to set up a short length of track on a piece of wood and hold the loco on the trackt so that you are looking along the track and the axles are at about eye level. Run the loco slowly towards and away from you and watch the coupling rods. If one crank pin on either side rises or falls before the other two then the quarter on that axle is out.

But I agree with Craig. That gearbox needs at torque reaction link. The link it's self should be horizontal and free to move at both ends. More information here

[Guest Max Stafford]

Darren. To be honest I'm amazed that you've got this far with this chassis. For good running, it's essential that the axle spacing and the rod spacing match perfectly. I suspect this may be the root of your problem. It's my experience with the 4mm DJH kits that the chassis frames and the valve gear etches are made on different planets and only on the CR 439 tank have I not encountered the most extreme difficulties.

If i were you, I'd cut my losses and buy a Comet etch. Then you will have axle and rod centres that match and you should avoid the kind of difficulties you are currently experiencing.

To be fair, the DJH body castings and etches are a very good basis for further work, but how they have got away with the rubbish that passes for chassis, particularly in the earlier 4mm kits for 30+ years is frankly beyond me!

 

Dave.

[John_Hughes]

Darren, a chassis that binds in one direction only is not uncommon; it usually points to a fault in the rods / wheels, but I've known it to be caused by bits of matter in the gears, or even a misshapen gear, so check this. But then if you're getting this frustrated and things aren't getting better, it's probably a good idea to take a very deep breath and go back to first principles.

 

Strip the chassis down so that just the axleboxes are in place, then check that each of the coupling rods is exactly right; the best way to do this is with a jig like the Perseverance ones (they come up regularly and cheaply on eBay, and are well worth acquiring, but there are other makes around as well which are almost as good, or if you have access to a lathe you could make your own). But it's best, as others have said, to use these when you install the horn-guides in the first place rather than fixing problems with them later.

 

If any of the rods is too short, it can be slightly lengthened by very gently tapping it along its length with a very light hammer; this is a standard jeweller's / blacksmith's technique; if it's too long then the only cure (apart from making up or getting new rods) is to open the offending hole(s) up and then bushing them to the correct dimensions.

 

Now, about those Romfords: first, it's not unusual for the crankpins to come out slightly wonky, but they're easy enough to straighten, and in my experience the pins are indeed always set at the correct distance. However, it's not impossible for even Romfords to be slightly out of quarter, so if everything else is right you can slacken off the cheese-head nut and try twisting one wheel on each axle at a time; you may get as much as a single degree of movement, which can make all the difference between smooth running and nasty binding.

 

Another problem is that one or more wheels may not be sitting absolutely square to the axle; spin them and check that they don't wobble, as any wobble will throw out the other vital dimensions; wobble can also mean that they bind against current collectors, springs or what-have you.

 

If the chassis is right, then it ought to roll absolutely freely when pushed along a piece of cardboard; if it doesn't then - as has been suggested - take off one set of rods and try that, then move on to the other; sooner or later the bind will become evident and you can fix it; but remember that the cure is hardly ever to open up the crankpin holes, assuming that there's just enough play in the rods to let them slide smoothly on and off the pins.

 

Only when everything is perfect should you start trying to get it to work under power with jump leads; if you're lucky it will go as to the manner born, so then you can add collectors and take ten minutes off to pat yourself on the back! The dogs will love your smiling face!

[gaf2u]

One and all,

Many thanks for all of the excellent advice. I have a wealth of things to go and try, but as suggested by Craig, I think I'll be contacting Comet shortly for a couple of etches. Might try rods alone first, before splashing out on an entire chassis and hornblock set.

 

I'm not sure if I made it clear, but I did fix the hornguides in place using Perseverence axle jigs, but I'm going to seize upon Dave's experience with DJH chassis, and maybe console myself with the possibility that I was fighting a losing battle from the start. I have a few other kits on the shelf, so prudence would seem to dictate sourcing alternative chassis before investing and wasting much time and effort.

 

The rods are removable Paul, and this was how I managed to get things rolling initially. I did have a tight spot on the rear left pair of wheels. Bill's suggestion around how to check quartering is a new a welcome one to me. The simple things always seems so obvious in hindsight!

 

John - I'll try your Romford trick, and as said, I had already straightened out one of the crankpins. I'll double check for any wobbles in particular.

 

Horsetan - I'd forgotten all about that problem you mentioned, and yes, I had exactly the same issue with the front footplate proving approx 1mm longer than the valence. After much head scratching, and after having consulted many photos, I elected to simply cut off the surplus. The forward rivet line is practically over the buffer beam but, as we say over here, wild horses wouldn't notice it as they gallop past.

 

Again, thanks one and all. I'll let you know how I get on

Darren

[gaf2u]

Eureka, eureka, eureka!

Removed the gearbox, did a lot of sighting through the crankpins at eye level with loco rolling as suggested, measuring all crankpins vertically off a plate glass base with lco stationary, and checked the quartering on one axle which looked a teeny bit off, so simply removed one of the two wheels and refitted it, whilst giving it a little torsional pressure when tightening the axle nut.

 

And away she flew. Running away sweetly in both directions on a rolling road now for 20 minutes and all appears to be well still.

 

I'd emailed Comet after reading all previous posts this evening and ordered a chassis pack too just in case. Won't go to waste as have another Duchess sitting on the shelf.

 

Thanks again, and I'll post some more pictures when she's fully assembled.

Darren

[John_Hughes]

Brilliant! Glad she's going now! I wish I had a quid for every set of Romfords I've seen which didn't turn out quite as easy to quarter as they look!

[Guest Max Stafford]

I always find that Romford/Markits wheels benefit from a very gentle bit of attention from a pointed file just to take any burring off the locating faces.

 

Dave.

[John_Hughes]

I always find that Romford/Markits wheels benefit from a very gentle bit of attention from a pointed file just to take any butting of the locating faces.

 

Dave.

 

Exactly! Some of them tend to be very snug indeed and need a little easing before they'll fit other than by brute force, but it's very easy to overdo it!

[Horsetan]

Horsetan - I'd forgotten all about that problem you mentioned, and yes, I had exactly the same issue with the front footplate proving approx 1mm longer than the valence. After much head scratching, and after having consulted many photos, I elected to simply cut off the surplus. The forward rivet line is practically over the buffer beam but, as we say over here, wild horses wouldn't notice it as they gallop past.

 

Thanks for confirming that. I thought it was just my sample which was flawed - but your confirmation may suggest an entire batch came out like this. I've worked out where I should saw out a section whilst still preserving the rivet line. Might also have to do something about the firebox casting on mine as the end profiles are not symmetrical.

[Captain Kernow]

A heartening story with a happy ending - good luck with the rest of the build. I have sometimes found the same kind of problem when building a chassis. Once I get everything running well, I always ensure that each wheel goes back on the same axle end and in the same configuration, if I have to strip it down again for painting etc. I normally mark up a piece of card and lay each component in it's correct place, prior to re-assembly.

[gaf2u]

Well, here's the finished article. I persevered with the DJH chassis even though I've since ordered and received a full Comet chassis pack. Took a little more work to get everything running really sweet, right down to crawling speeds. The float in the worm shaft on the Northyard gearbox is still a little concerning, but hopefully the torque link from gearbox to motor mounting eliminates any operating issues in this respect. On the other hand it was very easy to work with in that the flexible (rubber) drive linkage makes removing the motor simple, and the gearbox itself can be easily and quickly removed via the two lowermost screws on the sump plate, allowing you a rolling chassis in seconds.

In hindsight I should probably have fitted the gearbox to the centre axle and had the motor facing rearwards - this would have permitted me more space for a larger flywheel. I had forgotten how flimsy the DJH valve gear is, even though their etches are the same as Comet's at 15 thou (0.4 mm). Nothing is laminated however, which is maybe a large part of the problem.

Here's the evidence, first the completed and painted chassis.

 

A close up showing the torque link, parallel to and axially aligned with the drive shaft centreline. Per the note above, this arrangement makes motor removal very simple.

 

Finally, the assembled article. I'll not be painting the superstructure for a while as I'm living away from home for work reasons at present and airbrush etc. is still resident in my loft at home. I'm very happy with it, and will definitely employ the CSB philosophy again - takes a little bit more work but gives a smooth riding result. The wheel sets drop out on this model, once the brake assembly is removed via three retaining nuts. Took some effort but may prove fortuitous at some future time when an overhaul is required. All that it left is to fit some contacts. I fitted sprung plunger pick-ups to the insulated wheels, not realising that they would push the entire chassis over to one side when not balanced by an opposing set on the other side. I've read a number of posts here in which punters have advised against them, so I removed them and will use simple wipers instead.

 

 

Thanks for reading. Will be back again with more hopefully at some time in the future.

[Simond]

Resurrection of old topic!

 

I had a 7mm 1366 pannier which despite great efforts, and having done so when first built, would not run sweetly when going forwards.

 

The loco is kit built, fully sprung, with Fourtracks horns and Slaters wheels, and an ABC double reduction gearbox with a tiny (1620?) Mashima.

 

I searched the loco, and eventually RMWeb for the solution, hence finding this thread. Despite rattling up and down the track in either direction like a good 'un when given a reasonable shove, with the gearbox grub screw loosened, as soon as it was tightened, it would stop or struggle with the rods set about 5 & 2 o'clock.

 

I resisted the urge to open up the holes in the rods despite there being possible evidence that the right rear rod, and today I tried loosening the wheels and trying to requarter them per this thread. As expected, with Slaters wheels, nothing doing.

 

After much fiddling, fettling and cursing, I took the torque link off the motor and remade it. Problem solved!

 

Not sure what the issue was, as the link, which comprised a chassis mounted peg engaging in the slot between motor mounting plate & gearbox spacer rod, was not applying any obvious side loads, but it did have a little looseness between the peg (which was covered with a small length of plastic tube) and the slot in the gearbox - this allowed the motor to lift slightly when going forwards, but not moving when going astern.

 

The new peg is made from stiff wire, folded back on itself twice to fit a slightly larger diameter of plastic tube (lawn mower fuel pipe...) which fits snugly in the slot in the gearbox.

 

Hope this helps somebody!

Simon

[ScRSG]

Just out of interest as the posts don't seem to mention this, have you attempted to do this csb chassis in OO or is it EM?

[Horsetan]

Just out of interest as the posts don't seem to mention this, have you attempted to do this csb chassis in OO or is it EM?

 

It's OO.

[davefrk]

I would worry that in OO, CSB isn't the best way to go for a big loco. The frames and therefore anchor points are too close together and with a big top heavy loco like the Duchess the loco might have a tendency to 'wobble' from side to side. Okay, in EM the anchor points or if you like the wire springs, are only 2.5 to 3mm further apart but the same loco would be much more stable. I make my 0.5mm loco frames 15mm overall so the 'gap' between is 14mm allowing for CSBs, motors, gearboxes etc. 

If your Duchess is OO I would guess the DJH frames are about 11mm apart so the spacing of the CSB anchors would be very narrow.

 

Continuous Springy Beam suspension works beautifully but there are a few things to be aware of, the above one is important but as with all hornblock systems the centres of the rods matching the axle centres exactly is 'the' most important.

Just saying, in my experience of using CSBs for over ten years.

 

 

8F chassis under construction, 0.5 frames 14mm apart, good for 3ft radius curves. As seen in the CLAG, CSB gallery.

 

Dave Franks.

[ScRSG]

Mr Franks and I had a discussion on the above last night at our club, he seems convinced that in OO that the loco will wobble due to the closeness of the frames, although I could not fully grasp why this would be the case. There is only 1.7 mm difference in the gauge after all, but David thinks that the frames are up to 3mm closer together in OO and this is what would cause the problems. I look forward to hearing how you get on. We have considered using csb on small shunting locos to aid slow running and pick up etc. Our main concern was finding the right gearbox that would fit between the frames and the csb suspension parts, but you have come up with a solution to that dilemma!

Please let us all know how you get on.

[billbedford]

When in doubt follow the prototype.

 

LMS loco bogies had compensation beams between the axle boxes which made them soft in pitch and stiff in roll. They also had side bearing cups so that the loco frames were supported on the bogie frames*. This allows the bogie to control the roll in the loco frames. If you build your loco frames so that the front end is supported by the bogie side frames, then the body won't wobble.

 

* see this photo (mar11, second to bottom on page)