About 12 months ago when I wrote my first post on the Eureka 50 class http://philipscreek.blogspot.com.au/2015/09/eureka-50-class-early-impressions.html
I noted that the front pony wheels derailed on a few occasions. At the time, I thought the derailment was due to a track problem but the derailments have continued at various locations and I note that James McInerney reported a similar problem in his review in the June issue of AMRM.
James removed the spring which applies a downward pressure on the wheels, relying instead on the weight of the wheel assembly to prevent derailment. I also removed the spring but also opted to add a little extra weight to the wheels. I superglued two pieces of lead flashing onto the pony truck. The piece folded on the top was beaten thin to allow room for lateral movement.
The final challenge is one that I haven't not been able to resolve, specifically, the clicking noise in the drive mechanism. For my locomotive, the sound only occurs when travelling in reverse. A comment from Jim on my earlier post identified that the sound came from the second pair of driving wheels when counted from the front. From my investigations, Jim's observations are correct. I noticed that, unlike the other three driving wheel sets, the second pair allows some vertical movement as if the holes through the chassis was too large or a pair of bushes was missing. I have also noticed that the noise only occurs when travelling in reverse. The noise may be a consequence of the loose wheel set being realigned and slipping on the driving gear as connecting rods move through their arc.
However, all of this speculation does help resolve it and frankly, I can't see a solution beyond a significant dismantling of the drive assembly, something that is well beyond my skill set particularly without any drawings or schematics. Maybe instead, I should invest in a sound decoder that will mask the non prototypical noise with traditional steam locomotive sounds.