Model Railway Forum banner
1 - 8 of 8 Posts

·
Registered
Joined
·
43 Posts
Discussion Starter · #1 ·
I have a Bachmann 9f (the weathered version) and whilst it runs fine on the straights it comes to a grinding halt on curves (unless I run it flat out!).
With my layout only being 14' in length, double track, I have to use set track curves. I have radius 2 on the inside line & radius 3 on the outside.
Does anyone know if the 9f's wheelbase is too long even for radius 3 curves? Has anyone else experienced this problem? If its because I'm using set track and the curves are too tight for it then its going to have to spend its life parked in the depot! Or have I just got a duff loco? I do find that some of my steam locos do slow down considerably on the curves whereas diesels do not.
 

·
In depth idiot
Joined
·
7,681 Posts
Not a duff loco, just the mechanics of a long coupled wheelbase having to be got round a curve. The diesel chassis have considerable flexibility with a pair of independent short wheelbase bogies with centre gear coupled wheels. On the steamers the powered wheelbase is usually longer, and the coupling rods create binding as the wheels move laterally in the chassis for the curve: every additional pair of flanged wheels makes the effect worse, so your 9F will be worst of the lot. If you have not done so already, check that all the 9F's wheels have unconstrained sideplay and that all the coupling rod pins are lubricated, as this will help.

It may interest you to know that I loco motorised the original tender drive Triang Hornby 9F when it first came out, and that ran on a layout with mostly set track curves. Despite attending to the lubrication this loco wore through the coupling pin holes in the rods after a few years operation, and had to have them rebushed.
 

·
Registered
Joined
·
43 Posts
Discussion Starter · #3 ·
Hmm, thanks for that. Ah well I might have to consider selling it as its a shame not to use it. What your saying sounds spot on as my smaller steam locos are fine on the curves but the bigger they get the more they slow down.....or stop in the case of my 9f....
 

·
In depth idiot
Joined
·
7,681 Posts
Just one question about the 9F. On the straight, if you snap the power off (or even better run it into a dead section), from full power; how far does it coast on the flywheel?

The examples I have would all coast three to four feet when tested on DC ahead of decoder fitting. If yours doesn't coast that well there may be some tightness in the gear train, and that won't help when drag from a curve kicks in.
 

·
Registered
Joined
·
43 Posts
Discussion Starter · #5 ·
Not sure as I have never tried it but will try tonight & see what it does. If it does not coast and there is tightness in the gear train, will a long period of running at a fairly high speed slacken things off a bit? I guess its had less than 30 minutes use since I have bought it due to its inability to negotiate curves.
 

·
Registered
Joined
·
43 Posts
Discussion Starter · #7 ·
Ok well I have tested it, run at full speed & then shut the power off - it coasts for about 12 inches! I guess a good hour running at mid to high speed is the next step to see if that cures it.......

It may well be that the tight set track curves are not really suitable for steam locos, my K3 struggles a bit also and so do my others when hauling lengthy trains.
 

·
Registered
Joined
·
182 Posts
Of all the large steam locos I have tried, my Bachmann 9F Evening Star struggles the most on setrack curves, even radius 3,
it does not actually stop, but it does slow significantly.

I am in the, perhaps fortunate, position of being about to construct a new layout after a house move, I will still need to use setrack curves, but in the past year both Peco and Hornby (I think) have released radius 4 setrack curves, so I am thinking of using these for the outer mainline.

It depends on how 'finished' your current layout is as to whether a move to radius 4 curves could be accommodated with minimum disruption.

I have to say that, despite the problem, I am generally quite impressed with the 9F, the flywheel makes a big improvement to the general running characteristics.

Good Luck
Ashley
 
1 - 8 of 8 Posts
Top