Con rod issues

[T30RRA]

So got the chassis wired up and wheels turn fine. Added the con rods and now it won't budge. It's like it's seized up. It's a DJH 03 kit.

 

Is this a quartering problem? Wheels are slaters and I've gone for right hand lead.

 

Thanks.

[DCB]

Quartering or maybe the rods are the wrong length or maybe on the wrong way round. Usually there is a tight spot rather than the whole lot seized

[N15class]

Is there any movement at all?

 

Best place to start is right from the beginning.

1. Are the coupling rods and axle bushes at the same centres. And the coupling rods identical to each other.

2. Are the wheels mounted 90° to each other.

3. Are the crank pins square to the wheels in all directions.

4. Are the coupling rods a nice free fit on the pins, not sloppy.

5. are the crank pins long enough that when the nut is tight the coupling rods will still rotate.

 

With all the above correct it should rotate quite freely. But if it does bind you can find out why and where by gentle wriggling the coupling rods and look to see which side the pin is within the hole. It can generally be cured by easing one of the holes, but sometimes needs the axle bushes moving as the spacings may not still be quite right.

[Simond]

And one to add to Peter’s list that caught me - are all the wheels identical? Many years back I was building a kit, and I had an axle & wheels with a different crank throw to the others. That caused issues...

 

And if they are Slaters wheels, the boss of the wheel may catch on the rods, you need a washer or two between the rod and the wheel to provide clearance.

 

Are the rods jointed? What you have is effectively an 0-8-0, and it will be easier to break it down to smaller units.

 

Start be checking your wheels as above. Then without rods, confirm that all the wheels and the flycranks rotate freely.

 

Mark your rods with a felt tip to remember right & left. Keep them the same way round

 

If the rods are jointed, take them off two of the axles and try to run it (under finger power) as an 0-4-0. If the rods are not jointed, take out two of the axles. If it doesn’t run freely, try to find out why. You may have to open the holes in the rods slightly, but beware over doing this.

 

When the 0-4-0 works, you can try adding an axle (or the flycranks), and check that works, adjust only the fit to the latest axle, and when that works, add the final axle.

 

HTH

Simon

[doilum]

Try assembling without crankpin bushes. This will give you an idea of what is going on as you rotate the wheels slowly by hand.

[T30RRA]

Thanks for all the suggestions. I took the rods off altogether and it definitely turns without but the nuts were quiet tight. I've drilled the bosses again to clear out the solder from laminating and reassembled one side and left the nuts slightly looser than before and it now goes. Hopefully it will be ok when I refit the rod on the other side.

 

If all goes to plan I will just need to adjust the wiper pick ups. They on their own cause some reliability issues at present even just testing it.

[Michael Edge]

If you tighten the nuts on Slater's crankpins all the bushes move off centre, resulting in random out of quarter effects. To avoid this back all the nuts off about a quarter turn and secure with Loctite - this has been my routine with this crankpin system for many years. Loose bushes are a bit of a nonsense on crankpins, have a look at full size ones if you don't believe me.

[T30RRA]

Thanks Michael.

[Simond]

Better still, tap the Slaters bushes 10BA, and file flats on the flange, and fix 10 BA screws in the wheels, onto which you can screw the tapped bushes. See my Duchess thread for piccies.

 

http://www.rmweb.co.uk/community/index.php?/topic/129812-second-hand-duchess/?p=3115553

 

I have done this with every loco I’ve built, (20 or so and counting) it’s robust, accurate and reliable.

 

If you fix the screws in the wheels, don’t ever use Loctite as if you do, the bond may be stronger than the epoxy holding the screw to the wheel, and if you try to undo it, it will tear the wheel, which will necessitate a machining job (or replacement) to fix. If the nut comes undone, fix the cause, which is likely to be a binding crankpin/coupling rod journal. At most, use a tiny drop of nail varnish to stop any particularly irritating cranknuts coming undone, you can at least soften this with acetone, should you need to remove the nut.

 

Best

Simon

Edited November 11, 2018 by Simond

[N15class]

Do not slacken the nuts off. Find out why they can't be done up tight. Could be a burr under the crank pin around the screw, or screw not square to the wheel. Or the crank pin too short.

 

As Simon says clear nail varnish is a good nut lock.

 

Be careful using a drill to enlarge the hole. A 2 fluted drill will make a triangular hole. A broach or tapered ream are better. Or if all else fails a round needle file rotated backwards (this stops the teeth snagging, and a smoother finish). Work very gently from both sides, taking the minimum off each time until all is working smoothly.

Edited November 11, 2018 by N15class

[doilum]

Too late to help this time but for future kits?

Several kit instructions I have come across leave the fitting of con rods/ valvegear until it is almost an afterthought. Most scratch builders complete at least the con rods as they assemble the frames and perform the initial fitting of the wheels. This avoids complications from pick ups and drive gear. The chassis must sit squarely on all six wheels and whizz freely with the con rods in place.

[Michael Edge]

Do not slacken the nuts off. Find out why they can't be done up tight. Could be a burr under the crank pin around the screw, or screw not square to the wheel. Or the crank pin too short.

 

As Simon says clear nail varnish is a good nut lock.

 

Be careful using a drill to enlarge the hole. A 2 fluted drill will make a triangular hole. A broach or tapered ream are better. Or if all else fails a round needle file rotated backwards (this stops the teeth snagging, and a smoother finish). Work very gently from both sides, taking the minimum off each time until all is working smoothly.

 

The reason is that the bushes are a loose fit on the screws, tightening the nut moves the bush relative to the screw centre resulting as I said in random variations in crankthrow. Loctite threadlock comes off quite easily if heated a little and I lock the screws into the wheels very securely by countersinking the back of the wheel and filling with epoxy from the back.

[Simond]

I too make efforts to ensure the screws are well fixed, but I’ve seen the results of something applied to the nuts, might have been superglue, of course, but I’d guess loctite. David Smith did a very good set of posts on use of a dividing head & milling machine to recover a set of wheels where the pins had broken off, and as you may have seen, I had the same issue with a couple of pins on the Duchess, though I was able to get them out without recourse to heavy machinery.

 

I agree that the bushes can be fixed in a “circle of uncertainty” which can throw the quartering (and throw) out, if they are simply clamped to the wheel with a 12BA screw & nut, I don’t like that approach at all, though many respected modellers have used it for years, and don’t seem to have issues. I much prefer the 10BA screw, it’s stiffer & stronger,and has much more gluing area than the 12BA, and provided you’re careful tapping the bush, it’s pretty much going to be, and stay, concentric with the pin.

 

I think the key point is that if the nut or bush unscrews itself, there must be a reason, and it’s best, in my view, to fix the reason, rather than gluing the nut on, which addresses only the symptom.

 

Best

Simon

[T30RRA]

Thanks every body. As I imagined one problem solved another created....

 

The con rods don't seem to be an issue now and I have had it going in a stop start fashion but this is because I've now got wiper pickups to sort. I don't seem to be able to get reliable power through them from the backs of the wheels.

 

Should they sit flat against the tyre?

[Simond]

You can pick up from the tyres, but you’ll certainly pick up dust & fluff too. Backscratchers are pretty reliable (split axles are better) if set up properly. You need sufficient flexibility to ensure that the friction when fully compressed does not stop it running, and when fully extended still touches with enough force to transmit the necessary current.

 

Tyres, wheel backs and track needs to be clean enough too.

 

You might want to use phosphor bronze strip, Slaters sell it. Others use phos bronze wire. Otherwise I have used floating spring pickups, which can move from side to side with the wheel free play. Again, my Duchess thread.

 

HTH

Simon

[doilum]

Isn't the 03 a perfect candidate for plunger pickups?

[Michael Edge]

Thanks every body. As I imagined one problem solved another created....

 

The con rods don't seem to be an issue now and I have had it going in a stop start fashion but this is because I've now got wiper pickups to sort. I don't seem to be able to get reliable power through them from the backs of the wheels.

 

Should they sit flat against the tyre?

 

Use phosphor bronze wire and make sure that the wheel backs are clean, pickups on the tread get dirty much quicker in my experience.

 

I too make efforts to ensure the screws are well fixed, but I’ve seen the results of something applied to the nuts, might have been superglue, of course, but I’d guess loctite. David Smith did a very good set of posts on use of a dividing head & milling machine to recover a set of wheels where the pins had broken off, and as you may have seen, I had the same issue with a couple of pins on the Duchess, though I was able to get them out without recourse to heavy machinery.

 

I agree that the bushes can be fixed in a “circle of uncertainty” which can throw the quartering (and throw) out, if they are simply clamped to the wheel with a 12BA screw & nut, I don’t like that approach at all, though many respected modellers have used it for years, and don’t seem to have issues. I much prefer the 10BA screw, it’s stiffer & stronger,and has much more gluing area than the 12BA, and provided you’re careful tapping the bush, it’s pretty much going to be, and stay, concentric with the pin.

 

I think the key point is that if the nut or bush unscrews itself, there must be a reason, and it’s best, in my view, to fix the reason, rather than gluing the nut on, which addresses only the symptom.

 

Best

Simon

This is getting a bit circular, the nut only unscrews because I've backed it off to avoid the problem. If you want to follow full size practice more closely you could cross drill the nut/screw and fit a pin through them.....

[hartleymartin]

If you put pick ups onto the backs of the wheels try rubbing a 9B pencil lead onto those areas. It acts as a conductive dry lubricant but also helps prevents muck from sticking to the backs of the wheels.

[T30RRA]

Thanks everyone. Where the rods kick out for the piece that attaches to the jack shaft, the axle bushes don't go all the way through. Is it a case of using two bushes or do they need soldering together or something?

[Simond]

Hi

 

use two bushes, put one set on the pins, put the coupling rods on, put another one on the pin, and put the connecting rods on, and then washer and nut, if you're doing it "Slaters style".

 

You may need to shorten the bushes;  Easy way:

 

Put the bush on its fat end on your bench.

Make a hole in a thin piece of card or thick paper over it - the hole needs to be snug on the thin end of the bush.  Put the card over the bush. 

Put a coupling or connecting rod over that, face down.  Make sure your rod is face down or you'll scratch it!

Hold the rod to keep the bush from moving, and file the protruding end of the bush down til it's flush with the back of the rod. 

Take off the piece of card, and it will now have a running clearance.

 

HTH

Simon

Edited November 15, 2018 by Simond

[T30RRA]

Thanks Simon.

 

I laminated all the rods together so sounds like I will have to dismantle them.

[Simond]

Don’t understand why you would do that. Once they’re laminated, and cleaned up, they’re complete, normally.

 

I don’t have a picture to go with my explanation, but to try to amplify what I wrote, you don’t need to reduce the bushes very much, typically the narrow bit of the bush is about a millimetre longer than the rod is thick, you want to get rid of most of the excess, to ensure that when you tighten the crank nuts, the bushes are locked to the wheels, but they do not trap the rods so the wheels can still rotate.

 

If in doubt, take and post some photos and I’ll try to explain when I can

 

Best

Simon

[N15class]

If you posted pictures of what you have it may be easier to see where your problem lays. It sounds like you have outside cranks. If so this adds another set of problems.

[markjj]

This may be a very silly question but have you got the rods on the right way round ? The reason I ask is because of the drive crank under the cab. The rods may be slightly different spacing at one end if this makes sense. It's also possible you may have a twisted chassis as it's formed from one piece have you checked the Conn rods line up with the axle ends with no wheels fitted.

[T30RRA]

Some photos to try and show things. I did try 2 crank bushes soldered together which has improved things (thin end to thin end and outer fat end filed down to fit inside the rod) but now they do half a turn, stick, then the driving wheel has to be rotated to free it up. Then it does the same but in reverse. The jacks and front wheels don't seem to stick at all.