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Hornby L1 front bogie derailing


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  • RMweb Gold

One of the models I was eagerly awaiting last year was the Hornby L1. A top notch loco and mechanism - provided you ran it backwards. Going forwards (and I think only one review in a mag picked up on this?) the front bogie is far too light and easily derails going over points.

 

I think it's all down to the (all too) clever mechanism that allows it to look right in normal operation but also negotiate 1st radius curves?

 

I tried adding weight which had some success but it still wasn't perfect and had to negotiate some turnouts too slowly for realistic operation. There have been some solutions offered here and elsewhere but being quite ham-fisted was looking for something simples.

 

What I've not seen is this simple trick which I've tried and used for a few days. Quite simply take some card 1mm(ish) thick approx 24mm long and 7mm wide. It may be worth experimenting but the final dimensions probably won't be far off this. Score in the middle so you can fold into a 'V' or a pair of crocodile jaws, with the open end of the jaws towards the front.

 

The card here is white and doesn't show on my layout. You may want to use black or darken the card when you're satisfied but I left mine white for now to try and get a pic.

 

L1springa.jpg

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  • RMweb Gold

Thanks Il Grifone, you're probably right about the ageing process but as I say it's worked for a while. I don't have any PB sheet at the moment, just PB strips for pickups. Will add it to my list of bits and bobs to add to the general materials box.

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I think Hornby should recall them all and carry out a proper modification! Actually, I tried the solution suggested in an earlier thread of a phosphor bronze strip wedged through the fishtail of the front coupler and wiggled through the hole in the pony truck before being secured to the bottom of the chassis between the driving wheels - as I don't have any phosphor bronze strip I have used a bit of Evergreen 1.0mm plastic rod and it works, although I expect it will fail eventually. Must get some phosphor bronze in readiness - though I was told today that it is becoming difficult to get.

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I've three of the L1s, and as yet none of mine have derailed going forwards or backwards - however, I'm perplexed by the design of the L1 in this area. It seems to be extremely overengineered for something which was supposed to lead the driving wheels into the curves.

 

As Stewart said earlier, the pony truck doesn't have a central pivot as such - it has two pins for which the pony truck itself can slide/move around on two curved cutouts. This means it has some slack in all directions, meaning it's not actually working to a central point, with a radius of turning from left, to centre, to right, from that point, but from two points essentially and all of their turning radius along the length of the cutouts. My gut feeling is that the pony truck doesn't steer the locomotive into the curves so much as amble between the rails, and this may be partially the cause of derailments.

 

In contrast I am looking at a Bachmann O4, and it is a simple affair with a central pivot and a spring to push it down. I haven't heard any complaints in any form about the O4 derailing on RMweb (not to say it doesn't or hasn't happened) but it strikes me that this arrangement which is much simpler, will work better than Hornby's one on average, in all sorts of track conditions.

 

In short, Hornby's L1 pony truck is a strange bit of design, which I haven't had any problems with personally, but can fully understand why others are having problems. It's probably only a short amount of time before one of mine decides to jump the tracks, now that I've jinxed it...!

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When the L1 was 1st released, there was some discussion about this, and I saw one running on the Hornby demo layout at an exhibition, just prior to getting my own L1. Being aware of the problem, I watched it carefully. Every time it came out of a curve, the wheels did not straighten up! It didn't derail though....

 

Stewart

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  • 1 year later...

It does seem that Hornby have yet to fix this problem - my recently purchased L1 has the same issue on both trucks.

 

The back-to-back dimension is 13.9mm - has anybody discovered whether or not correcting this helps?

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Mine ran fine backwards but derailed tackling points going forwards. Cured mine by shoving a coil spring between the pony truck and the chassis. Seems to have been fine since.

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...The back-to-back dimension is 13.9mm - has anybody discovered whether or not correcting this helps?

 In with a chance of an improvement, bump out to 14.5mm and test. Won't cure the very silly fore and aft slop visible on reversing direction, as that is a direct consequence of the slack the mechanism requires.

 

This two pivot encumbrance is flaky: sometimes it will work, and yet a visually  identical specimen on the same design chassis is off practically every time it negotiates a diverging crossing with the pony truck leading. I first noticed this on a pair of same model number 8Fs bought together. Presumably the same batch, one ran all day with no bother, the other randomly fell off: and this on a layout with nothing smaller than the Peco medium radius point (nominal 36" radius) so it was hardly a stress test. It proved easy to lop off the two pivot tackle and fit a single pivot to the truck casting, instant cure.

 

Done that on all three L1s too as none of these were wholly reliable, two derailers and one that often had the pony wheelset visibly skewed. My third - and most recent - example of another Hornby chassis with this two pivot pony arrangement though is fine, haven't needed to tinker with the O1 at all, and there's no fore and aft slop either. Past experience however suggests that it might not be so if a second O1 is purchased.

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  • 2 years later...
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Bumping this thread in appreciation of the fact that, having found it in a search, the simple (within-my-capabilities) card solution at post 1 seems to work on the front pony on my Fowler 2-6-4T - so many thanks! 

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There seem to have been a few threads on this subject, I haven't seen this one before!

 

Here's what I did:

 

http://www.rmweb.co.uk/community/index.php?/topic/87326-Hornby-l1/

 

So far I've still only done the major rebuild on one of my three (although it wasn't that difficult!); the other two are still running with my initial modification (which in principle is quite like Metr0land's) and to be honest I don't notice much difference in the running of any of them.

 

With the original design I think it's important to check that the pony can pivot freely (I think somebody mentioned the possibility that the guides could be 'pinched' so that it doesn't), and also that the back to back of the pony wheels is correct.

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...With the original design I think it's important to check that the pony can pivot freely (I think somebody mentioned the possibility that the guides could be 'pinched' so that it doesn't), and also that the back to back of the pony wheels is correct.

Actually my one O1 on which this device operates completely successfully enabled me to understand the intent of the design when operating properly. The two gherkin shaped guides in the truck body need to narrow in the middle to only just let the two chassis pivots go through: then it works, snapping back into straight ahead when coming off curves; and the fore and aft slop seen when changing direction is practically eliminated too.

 

But all this is a solution seeking a  problem. As the many products with regular simply pivotted pony trucks demonstrate, it just isn't required. The basic principle on which the prototype was typically arranged unsurprisingly works reliably in model form.

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I think the idea behind the Hornby design is ingenious, in that it is self centring when running forward on straight track, whereas a conventionally-pivoted pony has nothing to stop it 'yawing' from side to side (a bit like pushing a wheelbarrow); it's just that the execution of it doesn't always seem to be as good!  With the L1 they seem to have arranged the geometry so that the theoretical pivot point is too near to the pony axle, whereas on the O1 it is further back and probably close to where the actual pivot point ought to be.

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  • 3 years later...
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Resurrecting this topic as I have a new perspective on the L1 front pony...  It is not just a problem that requires a spring... the double-pivot arrangement causes the pony to 'crab' at an odd angle to the rails when going round curves in the forward direction.  Visually it is awful, and unfortunately also causes problems with the new Peco Unifrog turnouts.  These have an electrical break right next to the frog throat (rather than farther down the switch blades as with that manufacturers electro frog points).  Consequently, the crabbing pony wheels cause an electrical short because the back of the wheel flange touches the switch rail at the same time as the wheel tread is in contact with the opposite polarity frog.  The only solution is to either make the pony run true (either by creating a new centre pivot or using a centring spring) or to create new electrical breaks on the unifrog points farther down the switch blades, well away from the frog/throat.

 

Similar issues are encountered with Hornby's O1 and P2 which have the same double-pivot arrangement to the front pony.

 

So there are incompatible tolerances being used between Peco and Hornby here -  We really could do with some industry-wide common standards, please.

 

That said, I do question why the Unifrog is used on Peco's OO bullhead rail turnouts, rather than just make them simple electro-frogs with rail breaks as per their flat bottomed rail product.  This newer track system is surely intended for a more advanced modeller, who will be unlikely to want a dead frog option anyway?

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Eliminating the 'two pivot' design is all that is required. As I posted earlier it's a (poor) solution looking for a problem.

 

A regular single pivot pony truck with a  coned tyre wheelset operates just as well on the model as it does on the prototype. And it is easier to spring, as the neat arrangement seen on Bachmann's models with leading pony trucks well illustrates. (Bachmann of course have a predeliction for a poor arrangement on the radial trucks of 0-6-2T, but that at least is quickly and easily fixed.)

 

And Hornby themselves should realise it is unnecessary: they have had a single pivot pony truck on their 9F from its introduction to their range, and more recently their K1 2-6-0 has a single pivot pony truck, which I rather hoped marked abandonment of the twin pivot encumbrance from newly tooled introductions to their range. On which thought:

 

Wait and see what the large Prairie gets.

Will it be a doubling of joy, or of regrets?

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