Erratic Running of Bachmann oo-gauge LMS Class 3F 0-6-0

[Coaldust]

    I purchased a brand-new Bachmann 00-gauge LMS 3F 0-6-0 tender locomotive about one year ago and noticed that it did not seem to run smoothly.  Thinking that it may have been a problem which would be solved by running-in,  I did not think too much about it at the time and after about a month I put my layout, which is portable, away and left matters for the next time.
     I have just re-assembled the layout and because the 3F was not running correctly decided to tackle the problem.  For every complete revolution of the driving wheels there was one point where some extra resistance in the motion presented itself.  At very slow speeds the loco would come to a complete standstill as the resistance occurred and for moderate speeds the loco would keep going but slow down every time the driving wheels reached the same point in the revolution.  At higher speeds there was no problem.
    I realised that the resistance must be something to do with the driving wheels or coupling rods rather than with the motor or gear train and so I decided to take the model apart.  I removed the bodyshell and took the motor out so that the wheels could be turned freely by hand.  At one point in the revolution the couplings rods were binding tightly against the crank pins on the front and centre pairs of wheels and this was the cause of  the resistance to motion.  The problem was not caused by wheel-wobble and there was nothing wrong with either the crank pins or the coupling rods. The binding was caused because the front set of driving wheels were out of adjustment on the quartering;  a quality-control problem at the manufactory.  Of course it does not matter if the quartering is not set precisely to 90 degrees so long as all three pairs of wheels are set to the same quartering angle.  For those modellers who are not sure what is meant by quartering the explanation is as follows. The crank pins on one side of a pair of driving wheels have to be a quarter turn in front of or behind those on the other side to keep the wheels running true - especially on a model loco where the driving wheels move the coupling rods rather than the reverse as on a real locomotive.
     In my case the centre and rear wheels were set to almost exactly 90 degrees, as checked visually,  but the front pair of wheels were nearly 10 degrees out in the quartering.  I found that it was quite easy to check the quartering as follows.  If  the driving wheels are rotated by hand to a position where on one side of the loco the coupling rods pass exactly over the wheel centres (imagine the piston to be at the full extent of its travel in the cylinder) quartering can be checked by eye and it is easy to see where the problem lies by checking the crank pin positions on the other side of the loco. To correct the quartering I found that it was possible to slightly rotate a driving wheel on its axle by moderate hand pressure. Quartering has to be quite accurately set on a new model.in terms of all three pairs of wheels being set the same. If the quartering is out by only 2 degrees on one pair of driving wheels on a brand new loco it will give problems.  Of course if  the problem is ignored the running will very gradually improve as wear takes place in the motion but this is never the answer.  I suppose that if I had sent the model back to Bachmann they would have been pleased to charge me for the cost of putting it right.  Unfortunately, these Chinese-produced models do not seem to be subject to the same level of quality control in manufacture as was the case when the models were produced in Britain and modellers seem to have to sort most running problems out themselves.    Progress!!!!!!!
    I can now report that the running problem has completely been cured and the model runs smoothly at the slowest speeds.  I know that, unfortunately, running problems are  not uncommon with manufactured models and hope that my own experience may be of some little help to others.