Bunkerbarge
The story of my own Hornby Thompson L1 is a lengthy one involving an Ebay claim, a burned out DCC decoder and a whole host of other challenges however, amongst it all, was the issue that this model seems to share with a lot of other owners and that was its alarming tendency to throw itself off the track with disturbing regularity.

After sorting out all the other items I found myself still left with a loco that didn't seem to like going over points so, after the small fortune I had spent on the loco I decided that it merited a very thorough investigation.  I even filmed it going around the track and studied the video in slow motion!

After all the studying and investigation what I thought was going on was this.  The loco is fitted with an unusual front bogie pivoting system.  Rather than a single central pivot it has two curved slots on either side with a pin in each.  Quite what the reasoning is behind this arrangement I'm not so sure, whether it is to allow traversing smaller radius curves or what I am really not so sure however what I did discover was the fact that when the locomotive comes off a curve the front bogie frequently does not realign itself with the track and happily runs along the straight with the bogie not perpendicular to the track.  The next time it comes to a point the misaligned bogie catches the blades of the point and ejects the loco.

I read up a lot of forum reports about this, apparently well known, phenomenon and first of all purchased a spare front bogie for the loco.  This was adapted to do away with the pin arrangement and use a central pivot to rotate the bogie.  I actually did expect this to work as there seemed to be many reports of success with the method but, very surprisingly, it didn't for me.

What I therefore decided to do was leave the bogie in its original configuration but introduce a device that would ensure the bogie realigned itself correctly after it left a curve.  Studying the area led me to realise that there was a suitable location for a sprung arm and a corresponding location for a sliding block to be added.  I manufactured a fine spring link from some thin gauge wire, bent the end around a former to suit the front screw and loosely fitted it with the screw in place but not tightened.  I then measured up the wire and drilled a hole through a small piece of plasticard to suit with a sliding clearance.  This piece of plasticard was then glued with some cyanoacrylate glue to the front bogie.  The tricky bit was to then refit the bogie while sliding the wire through the hole in the plasticard.  When the bogie was in place the screw holding the wire was tightened, ensuring the wire was perfectly aligned with the loco centre line.

When I tried the loco I was really surprised at just how effective it is.  The bogie now always re-aligns itself when it comes off a curve and it never derails on a point.


Thompson L1 b.jpg 
Thompson L1 a.jpg 
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Julian
Neat, simple and very effective; the best solutions are almost always thus.  Thank you Richard, the solution  may well suit other front bogie problems, too.

Regards

J
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Hugh Macnaughton
Many thanks. Will be on the tools on return from short break.
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AHJAY
An elegant answer... Nicely explained and really useful.

I do this sort of thing with all of my larger brass 4-6-2 tender locos so that the bogie properly leads the loco into a curve. I also use a slight downwards pressure on the wire to ensure positive bogie tracking. Without some form of guide like this, large locos seem to visibly "tack" into the corners like a Yacht. They look much better with the guidance.

BTW - is it just the "Photo-pose" or is the rear bogie tracking a wee bit stragely? (rear axle)

I hadn't bothered doing any RTR locos yet but being prompted by this post I will start on one or two of them. Thanks

regards, Ahjay
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Bunkerbarge
Thanks Ahjay, I suspect the loco wasn't on the track properly for the picture and I hadn't noticed.  It normally works smoothly, in fact it is now one of my favourite locomotives.
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AHJAY
Deserved. I really do like the simple no-nonsense approach you took, B-all change to the loco as bought, easy for others to follow and right on the money engineering-wise too. It will encourage others which is excellent!

Ahjay
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