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Front Pony Truck problem on Bachmann Crab and Hornby 8F


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  • RMweb Gold

Having a bit of a problem with front single axle trucks on a couple of models - a Hornby 8F and a Bachmann Crab - and I wonder if anyone can offer a tip that might help the riding characteristics please. The 8F and another model, the Bachmann Ivatt 2-6-2T, initially displayed poor running with the front bogies jumping the track when entering the curve (L or R) on Peco code 75 points. I don't have any similar problems with a whole range of other locos and I don't think there is a problem with the track laying.

 

The initial problems on the 8F and 2-6-2T were quickly cured by adjusting the bogie wheel back to backs. However, even after sorting that, the Crab bogie still regularly jumps on the points and also on tight curves - it seem the bogie is very light and possibly lifting slightly. Although it is not normally run on those it does seem to indicate there is a problem - it is not fouling the steps or cylinders. It seems that the springing arrangement does not really push down much to keep the truck on track. The 8F is now not as bad as the Crab and will run forward over the points very smoothly but still does not like pushing wagons forward when shunting. As the layout operation requires some use of these locos to run forward pushing wagons over the points so the added resistance naturally increases the likelihood of derailing as the load increases. I have no problems with any of the locos with 2 axle bogies.

 

I think that adding some weight to the bogies seems to be the best fix and I wondered if someone could offer any suggestions on the easiest, neatest way to do this (or, of course, any alternate solution). Thanks in advance.

 

Don

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The Bachmann pony truck should have a flat spring bearing on it to keep it stable. I don't have this particular model, but do operate the Bachmann BR stds 4 and 9,  Ivatt 4MT, Fairburn 4MTT,  K3, O4, O7, V2; all with leading pony trucks of the same basic design on a mixture of code 100 and 75 streamline, and various code 75 kit points, with complete success.

 

The only time they have given trouble is when as received the spring is exerting little to no loading, (or the spring is out of position and not engaging the truck frame: which typically means it was exerting little to no loading) and then the pony truck will bounce off the road all over the place. Bend the spring so it loads the pony truck and stays engaged, problem cured.

 

The Hornby 8F has the 'two pivot' truck design. I feel this is bad news as a design. It seems to be somewhat unpredictable, I had two identical 8Fs, same batch, bought at the same time. On one the thing fell off the road whenever it could, the other was stable; the skewing of the 'bad' pony truck on exiting curves was very marked and it would go awry very readily on a network of facing points. I also didn't like the fore and aft slack of about 2mm between forward and reverse, a visual nonsense when operating.

 

Couldn't detect 'the difference' that must have existed, but simply converted both to single pivot by hacking off all the two pivot tackle, drilling a pivot hole in the bogie frame, and using a small self tapper to create a new pivot in the keeper plates. Completely reliable, the weight of the rather lumpen Hornby casting is more than adequate for roadholding, even with some of the extraneous forward parts cut away for better appearance. (The otherwise delightful Hornby L1 is in the same case, likewise all converted to single pivot; interestingly on the Hornby O1 there is no fore and aft slop on my example and it behaves perfectly: however butchery awaits on the first inkling of misbehaviour.)

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I had exactly the same problem with my Bachmann Crab, and the answer is as set out above - adjust the spring to increase pressure downwards and make sure it is seated properly. The seating is important, and its very easy for the spring to be out of place. I seem to remember something similar with one of my Bachmann 9F's as well.

 

John.

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  • RMweb Gold

The Bachmann pony truck should have a flat spring bearing on it to keep it stable. I don't have this particular model, but do operate the Bachmann BR stds 4 and 9,  Ivatt 4MT, Fairburn 4MTT,  K3, O4, O7, V2; all with leading pony trucks of the same basic design on a mixture of code 100 and 75 streamline, and various code 75 kit points, with complete success.

 

The only time they have given trouble is when as received the spring is exerting little to no loading, (or the spring is out of position and not engaging the truck frame: which typically means it was exerting little to no loading) and then the pony truck will bounce off the road all over the place. Bend the spring so it loads the pony truck and stays engaged, problem cured.

 

The Hornby 8F has the 'two pivot' truck design. I feel this is bad news as a design. It seems to be somewhat unpredictable, I had two identical 8Fs, same batch, bought at the same time. On one the thing fell off the road whenever it could, the other was stable; the skewing of the 'bad' pony truck on exiting curves was very marked and it would go awry very readily on a network of facing points. I also didn't like the fore and aft slack of about 2mm between forward and reverse, a visual nonsense when operating.

 

Couldn't detect 'the difference' that must have existed, but simply converted both to single pivot by hacking off all the two pivot tackle, drilling a pivot hole in the bogie frame, and using a small self tapper to create a new pivot in the keeper plates. Completely reliable, the weight of the rather lumpen Hornby casting is more than adequate for roadholding, even with some of the extraneous forward parts cut away for better appearance. (The otherwise delightful Hornby L1 is in the same case, likewise all converted to single pivot; interestingly on the Hornby O1 there is no fore and aft slop on my example and it behaves perfectly: however butchery awaits on the first inkling of misbehaviour.)

 

I really appreciate your detailed response. Thanks.

 

I had noticed the spring on the Crab as it was originally out of position as you suggested was possible - that was when I first ran the loco out of the box - I had already positioned it correctly without adjusting as it did seem to apply some pressure. I wasn't sure about bending it to apply more pressure so I had left it which was when I wrote my post.

 

I fully accept the reasoning in your advice above and so today I removed the spring and carefully (and slightly) bent it to apply more pressure on the truck. I reassembled and tried again - no good. 2 or 3 further adjustments and no progress. The puzzling thing is that it seemed inconsistent as to where it derailed. At one point it went perfectly over the reverse curves of 2 facing points and then a following double slip but then promptly fell off the road on the straight facing part of the next point.

 

I had noticed that the truck and spring fit over a spigot to allow them to pivot when the holding screw is tightened. Examination suggested that this may be binding. As a first check I removed the spring completely. Without the spring in place the truck swiveled much more freely. Track testing then surprisingly proved perfect! I have run it up and down over all my pointwork for 20 mins without any derailment at all (so the tracklaying can't be too bad!). Finally it pushed a train of nine wagons through the points and round a tight curve without any problem at all.

 

So, it seems, against all of our applied logic that this particular Crab runs best without weight or spring!

 

It, I think, comes back to a combination of problems related to the spring itself. This one did seem to bind around the pivot somewhat and I could improve that by easing the hole. However it is also necessary to take into account the tension in the spring as if it is overdone it can stop it from lying flat when in position under the screw mount. So that when the screw is tightened down it can act like a spring washer under the truck pivot and there is a danger that it binds the swivelling of the whole bogie which is what I think is happening here. (I hope I have explained that clearly enough).

 

I fully accept that the normal solution would be to increase the spring pressure but it seems it is necessary to be aware that this does not cause an unintended further problem in this way. It is necessary to make sure that the spring lays flat around the screw under the bogie pivot. Not sure whether to bother with this now though as all seems to be OK at this moment. I am not keen on fixing what doesn't appear broke anymore!

 

Edit: Later examination of the spring under a magnifying glass shows a distinct kink around the screw hole. It appears that the spring may have been twisted in some way while screwed in place causing it to distort. This almost certainly the cause of the binding referred to above. I am confident I did not do it when I first moved the spring into its correct location and it was fully removed when I adjusted the spring pressure (gently by hand only). The fact that the model came out of the box with the spring out of position suggests to me that this problem was caused at the factory somehow. Well past warranty now though and it runs fine - I can always replace the spring with a new part.

 

On to the 8F next! Wonder what that will show. I have taken note of your comments and will look at it carefully shortly.

 

Thanks again.

 

Don

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  • RMweb Gold

I had exactly the same problem with my Bachmann Crab, and the answer is as set out above - adjust the spring to increase pressure downwards and make sure it is seated properly. The seating is important, and its very easy for the spring to be out of place. I seem to remember something similar with one of my Bachmann 9F's as well.

 

John.

 

John

 

Thanks for your response. I haven't got a Bachmann 9F although it is on the wish list so I will look out for that.

 

Please see my response above for the story so far!

 

Don

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  • RMweb Gold

 

The Hornby 8F has the 'two pivot' truck design.

 

Couldn't detect 'the difference' that must have existed, but simply converted both to single pivot by hacking off all the two pivot tackle, drilling a pivot hole in the bogie frame, and using a small self tapper to create a new pivot in the keeper plates. Completely reliable, the weight of the rather lumpen Hornby casting is more than adequate for roadholding, even with some of the extraneous forward parts cut away for better appearance. (The otherwise delightful Hornby L1 is in the same case, likewise all converted to single pivot; interestingly on the Hornby O1 there is no fore and aft slop on my example and it behaves perfectly: however butchery awaits on the first inkling of misbehaviour.)

 

Can you please advise where such small self tappers can be purchased? I realise that this one would probably be bigger than the usual screws used on 00 models but I have been looking for a source of a range of screws that can be used in place of manufacturers fittings - usually because they get lost, sometimes broken. Other times larger ones needed where the original thread has been damaged and, sometimes, like this when a new screw is needed. I have not been successful in locating such a supplier. If someone could offer a "kit" including a range of typical modelling screws then I feel it would be very useful to many of us.

 

Edit: Thinking again though, I guess that there is too big a range of screws used by the manufacturers to be able to do this. However a range of small self tappers would still be very useful.

 

Don

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  • RMweb Gold

 

The Hornby 8F has the 'two pivot' truck design. I feel this is bad news as a design. It seems to be somewhat unpredictable, I had two identical 8Fs, same batch, bought at the same time. On one the thing fell off the road whenever it could, the other was stable; the skewing of the 'bad' pony truck on exiting curves was very marked and it would go awry very readily on a network of facing points. I also didn't like the fore and aft slack of about 2mm between forward and reverse, a visual nonsense when operating.

 

Couldn't detect 'the difference' that must have existed, but simply converted both to single pivot by hacking off all the two pivot tackle, drilling a pivot hole in the bogie frame, and using a small self tapper to create a new pivot in the keeper plates. Completely reliable, the weight of the rather lumpen Hornby casting is more than adequate for roadholding, even with some of the extraneous forward parts cut away for better appearance. (The otherwise delightful Hornby L1 is in the same case, likewise all converted to single pivot; interestingly on the Hornby O1 there is no fore and aft slop on my example and it behaves perfectly: however butchery awaits on the first inkling of misbehaviour.)

 

Have now looked further into behaviour of 8F and I think you have explained everything. It seems quite appalling in the way the bogie jumps about - both sideways and backwards and forwards. I don't think I can accept it and would like to make the mod you suggested. Do I assume that it is necessary to remove the wheel keeper plate underneath the loco? I would guess that is the easiest way although a bit of a pain.

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  • RMweb Gold

I had a problem with the Hornby L1 front pony truck jumping off the tracks when going forwards.  It's a very low tech solution but you may want to try something like this first as it's stood the test of time?

 

http://www.rmweb.co.uk/community/index.php?/topic/51794-Hornby-l1-front-bogie-derailing/

 

Thanks for that reference. I will give your solution a try tomorrow.

 

I did a search on this forum to see if this problem had come up before I wrote my post but unfortunately did not locate your thread. I had not been aware that this was such a common problem on so many locos for so long and am amazed that this design continues to be used in production. It is certainly is causing rough riding on my 8F.

 

Thank you again for the information.

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 The Hornby two pivit pony truck is retained captive on the pivots between the upper and lower keeper plates. Usually only the nearest keeper plate screw has to be removed, and the lower plate flexes enough that the truck is released. Quite why Hornby persist with this poor design is a mystery. Modified to single pivot the locos still work on set track, and they have items in their range such as the 9F - longest chassis with a pony truck - that have always been single pivot and work perfectly well. Looks like it sneaked in and somehow got established  as an article of religion, and has never been properly challenged as unnecessary since.

Can you please advise where such small self tappers can be purchased? ...

I last bought a pack of 'mixed small sizes for repairs' in Mole Valley Varmers at Holsworthy, Devon. (This is a most excellent shop, where everything is dirt cheap because Varmers are all very very poor folk, who can barely afford their fifth Range Rover.) Also bought a twibble head and pickaxe helve and some steel toecap boots, and got a free harrow tine thrown in, on offer that day. Good chunk of steel which is bound to come in useful someday.

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Quite why Hornby persist with this poor design is a mystery.

For as long as I can remember they and their predecessors were chancers and still get away with it. One only has to look at the Hornby Stanier valanced Tender, Fowler drivers on a Stanier 2-6-4T and a Black Five that stands too high. The 8F pony truck looks to be on the L1 2-6-4T as well and so no doubt I too will have to tackle the problem now my layout is a roundy. The pony pivot point is too close to the axle. Didn't have any problems with the Bachmann Crab or 2-6-2T on curved points when I had the a layout based on Diggle but seeing as these points along with 24" radius points are all over the latest layout, it will be interesting to see what happens.

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  • RMweb Gold

 I last bought a pack of 'mixed small sizes for repairs' in Mole Valley Varmers at Holsworthy, Devon. (This is a most excellent shop, where everything is dirt cheap because Varmers are all very very poor folk, who can barely afford their fifth Range Rover.) Also bought a twibble head and pickaxe helve and some steel toecap boots, and got a free harrow tine thrown in, on offer that day. Good chunk of steel which is bound to come in useful someday.

 

Yes, I remember them. Visited many years ago when my folks lived in Devon - they were not Varmers though! Looked on their web site and they have some self tappers but not the ones you list. However I have now located and ordered some from Modelfixings - I didn't spot them on previous searches but they seemed to have some suitable screws and quite a good range of interesting fixings for modelling.

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