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Help, loco "waddling" side to side Bachmann 4MT


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  • RMweb Gold

Hi,

 

I've been bought a Bachmann 31-105 BR Standard 4MT 4-6-0 which wags violently from side to side when running in either forward or reverse.

 

I've had a look at the motion and valve gear, which all seems to be in order, and I've even tried removing the connection rods to see if it was those which were bent, but it still does it.

 

When not on the track, the wheels seem to be straight, and vertical, and move freely from side to side as they are supposed to.

 

As far as I can tell it is the rear set of driving wheels which cause this, although it could be the fronts, it's a bit hard to tell, although it definitely seems to pivot about the centre driving wheels.

 

Before I strip it down any further, has anyone come across this issue before, and anyone know the cause, and how to fix it?

 

Thanks very much,

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Sounds like a miss aligned axle or the back to back needs checking, I had an airfix tank that done the same and found a wheel wobble to be the cause.

Power it up upside down and you may get a better idea what`s happening

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Another vote for look at it running while inverted. Could be something really simple like a pick up or other bit of chassis hardware like a brake shoe or sandpipe catching on a driven wheel and displacing it sideways: that usually leads to an audible click though, and you haven't reported that. A wheel not properly seated on an axle, bent axle or crankpin, damage to a driven wheel tyre, bent coupling rod, one wheelset out of quarter, these are all possibilites.

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  • RMweb Gold

Thanks for the replies.

 

Yes, I will have to try running it upside down, but there is nothing immediately obvious.

 

Anglian, although new to me, it is I believe quite an old model - I think it's one of the "split-chassis" models.

 

34....B&D (i'm not typing all that!) no there's no click.

 

I thought I had read somewhere that this was a known problem with certain Bachmann models of that age, but I did a search before posting and couldn't find the thread referring to it.

 

It's a shame, as it's a lovely loco.

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I had this problem a few years ago with the same loco and asked the same question. A number of answers were all very similar.

 

These models didn't have all-metal wheels, they had plastic spoke inserts, and these had bowed outwards slightly with age, causing the coupling rods to foul them. The answer was to remove the coupling rods etc., prise out the inserts and then glue them back into place and press them flat until set. Refit coupling rods etc. and job done.

 

Hope this solves your problem

Keith

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Have a look at the plastic wheel centres, are they flat across the wheel face?

I have a couple of these and a couple of B1s about the same vintage and for some reason, I suspect reaction between the plastic wheel centre and (factory applied) lubricant, the centres have bulged outwards and are pushing the coupling rods or wheels sideways. It seems to be particularly bad on the rear driver, for some reason. Another B1 I came across was so bad it was locked up solid. These locos have spent almost all their lives in boxes, no home layout and the club one is taking rather longer to build than expected. They have never had any other lubricant applied. Doesn't seem to happen with any other locos.

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...I think it's one of the "split-chassis" models...

 Ah, that explains all. Completely normal for the type. Could be the bulging inserts mentioned, could be a split axle assembly breaking up, or both. Or something else yet again. This design of chassis is just a time bomb of potential problems which will progressively surface and need repair. They deteriorate left unused, the plastics used are unstable either of themselves or with assistance from the lubricants. It is a short life constructon. My best advice:  use the model as set dressing on a layout (as a loco on shed day for example).

 

Just call me 34C, that's what I wanted to be, but the system refused...

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  • RMweb Gold

Thanks again to all of you.

 

bizmad and great central, thank you both, that's the explanation I remember reading but couldn't find today.

 

34C (thank you) I think I'll investigate a bit further now I know what I'm looking for, but if as you suggest the loco is beyond saving then I might weather it up as a non-runner, and buy a more modern replacement. I think I'm right in saying that Bachmann did a later re-chassised version of the Standard 4MT which was DCC ready, so I will keep an eye out for one.

 

Cheers,

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...if as you suggest the loco is beyond saving ...

 When they were the only game in town for RTR models of certain key types, I went to the trouble of keeping them going. Aralditing together the driving wheel insulators and half axles into solid wheelsets, removing those wheelface inserts, trimming them and gluing back in place, and several other tweaks and repairs. They required at least annual service to clean out the bearing surfaces to maintain efficient current collection. And then the plating wears through on the tyres, stub axles and chassis bearing surfaces, conductivity becomes very flaky: the chassis is effectively all used up. It is possible to make reliable runners out of these things, but they require a servicing progamme to do it, and if operated regularly then wear out completely.

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  • RMweb Gold

 When they were the only game in town for RTR models of certain key types, I went to the trouble of keeping them going. Aralditing together the driving wheel insulators and half axles into solid wheelsets, removing those wheelface inserts, trimming them and gluing back in place, and several other tweaks and repairs. They required at least annual service to clean out the bearing surfaces to maintain efficient current collection. And then the plating wears through on the tyres, stub axles and chassis bearing surfaces, conductivity becomes very flaky: the chassis is effectively all used up. It is possible to make reliable runners out of these things, but they require a servicing progamme to do it, and if operated regularly then wear out completely.

 

Yeah, having looked more closely, the surface of the wheels is pitted, all the driving wheels are catching on the connection rods at certain points of rotation, and if it tries to go round a bend (radius 3) then it locks up solid.

 

I think it will be retired.

 

Thanks for all you help and advice.

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There are issues with all Bachmann split chassis engines.  With time (even when the engine is kept in a cabinet!) the nylon joiners that connect the driving wheels together will fatigue and split allowing the wheels to loose their quartering and spread - catching the adjacent rods. If you go to the Bachmann web site you can order replacement joiners at a much lower price than from another well known spare parts retailer on eBay.  The nylon spacers / gears are a simple push fit onto the wheels - no glue just a force fit.

 

If the engine is good cosmetically then buying replacement spacers is a cheap option.

 

Good luck

 

Ray

 

http://longsheds.blogspot.co.uk/

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