Help! Wheel binding

[SJS]

Dear all - I am hoping someone can help me. I am attempting my first EM gauge loco using a High-level kits chassis and Gibson wheels. My first attempt was a disaster - lack of general skills I believe and although it looked good it didn't run at all. So I made a second go. Now it seems a lot better (doesn't look quite as nice though!) but the wheels bind when turned by hand (its a 0-4-2) so its only one set of rods. I believe they are quartered correctly but the binding continues. The odd thing is that it seems to change where it binds depending on how I try turning the wheels. I.e., if I turn the rear pair it binds somewhere different from turning the front.

 

I have looked online but being a newbie at this kind of building I am not sure what to do and in what order. I don't want to make things worse so any thoughts?

 

S.

[Spitfire2865]

Take the rods off, does it free roll freely and straight without wobble?

If it curves to one side much, thats a sure sign the wheelbase doesnt match the rods.  

[SJS]

thanks Spitfire - I took the rods off and it doesn't seem to curve although I must admit it perhaps doesn't roll as freely as it should.... 

[SJS]

OK so I took everything apart and noticed a bent crankpin - so rebuilt it. Its now much better - in fact it runs fine if I loosen one of the locknuts so the coupling rod is out of the bush. This would suggest to me that I need to loosen off that coupling rod a little? Thoughts before I do this?

 

Thanks, S.

[34theletterbetweenB&D]

Introduce the slack in the bushes if possible, as these are easily replaced components.

[Torper]

The holes in the coupling rods should not be a tight fit on the crankpin bushes. If they are, open them out a little, but not too much - the rods should slide onto the bushes without interference.  It's astonishing how much coupling rod/bush slop there is on RTR locos and they usually run beautifully although I wouldn't recommend you go quite that far!

 

DT

[SJS]

Thanks everyone - I did introduce some more slack into the rods and things are moving much better now. I think I am somewhere between a finely-crafted model and an RTR in terms of the slack!

 

Hopefully I will get it running in the next few days!

 

Thanks again, S.

[Il Grifone]

The coupling rods have to be exactly the same as the wheelbase and obviously the crank throw has to be identical on all the coupled wheels. If you have two Romford axles it is easy to lay the rods on the threaded section of the axles and check. Ideally there should be a minimum of slop - just sufficient for the rods/axles to revolve. Avoid the bodge of filing the coupling rod holes oval, especially with a four coupled mechanism.

[The Johnster]

It is vital that the centres of the crankpin holes in the coupling rod are identical to those of the axle holes in the frames.  If your High Level kit included coupling rods they should be identical as supplied, though there is a little scope for inducing 'slop' by opening out the coupling rod crankpin holes slightly.  These centres are critical and liable to inaccuracy as they do not sctually exist once the respective holes have been drilled out (!) and the drilling may have induced a bit of error especially if it was done by hand and not with a machine tool where everything is held very solidly in position.  There may also be a little error if you are using coupling rods from the original RTR model; I am not wholly conversant with what is supplied with a High Level kit.

 

The answer, as you seem to have found, is to ensure everything is square and as close as possible to it's intended position, and allow sufficient play or slop for free running.  As David says, if you do 'ease' the coupling rod holes keep them circular, and check every so often for wear if the loco is used for heavy high mileage work, though this doesn't sound like an 0-4-2T's job in general...  

 

Slop on RTR locos is often considerable but they have to be capable of running round much sharper curvature than you will usually be using on an EM layout, not to mention being designed for convenient volume production and assembly, and you can probably get your loco running perfectly well with a lot less slop than this!