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· In depth idiot
8,808 Posts

I hadn't noticed this thread before, nor seen any other reviews of Bachmann's 'Tibet' production, so this was interesting to read.

Regarding the running problem you write: "but it seems that the centre axle of each bogie is positioned slightly lower than the outer 2 meaning that it rocks back and forth and the 6 wheels don't seem to sit on the rail at the same time."

Looking at the pictures of the chassis in your review, the general construction looks to be in the same style as the Bachmann UK product, so it is probable that this problem which has been noted on some UK 3 axle bogie models arises from the same cause. First thing, check with your steel straightedge that your perception that the centre axles sit low compared to the outer axles is correct. If it is, then (working on the assumption that the construction is similar to that of the UK models,) remove the outer cosmetic frame of the bogie, to access the wheelsets; the brass bearing collars of which are clipped into the plastic housing at the bottom of the bogie gear tower. Try opening the diameter of the location for the brass collar of the centre axle for an easy fit; that was all that was necessary on the model I tinkered with for this problem. A minutes work with a small rat tail file, check that the wheels sit on a common plane, and you are done.

My suspicion is that is the quite tight 'clip in' action of the brass bearing collar of the centre wheelset which causes the problem. If you think about the mechanics of it you will see why: the housing is made in a fairly elastic polymer, and when the centre brass collar is clipped in the housing deforms in response, causing the ends to curve upwards.
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