[aaronoxford77]

Greetings all. I have a problem. I'm the owner of the Dapol 2D-007-000 class 66 number 709 MSC livery and I've discovered that it derails on every curve on my model railway, but the thing is, only in 1 direction! Now I have had a look at it numerous times, and nothing seems to be visible that would be causing it. I've checked gauging, and it's fine. Do any of you know what the cause might be? I'm considering just withdrawing it, replacing it with something that works properly. It's been back twice for rectifying and it's not working. Help! Thanks.

 

[34C]

There are two very likely independent possibilities for the cause of the problem described:

Limitation of bogie movement, both rotation and pitch, such that in one direction the mechanism cannot adjust to the track curvature. Such limitation can be caused inside the body shell, as well as externally by such as fouling of a coupler on body work or detail limiting movement.
The derailment is only in one direction, is this with respect to the track or the loco?
Does the derailment only occur with either of the A or B cab leading, or is it only in one direction on the layout, whichever cab leads?
What happens if you trial the mechanism with the body removed?

Then there is the track, does the derailment always commence at one location?
If so observe that location very closely.


And then there is 'interaction'
If this loco is the longest six axle model you operate, and all other traction and vehicles are derailment free, then you may be looking at a subtle track alignment problem which just pushes the larger unit 'over the edge'.
You may need to test independent of the layout to see if the loco is problem free on the same radius curve; and if it is then re-lay the track in the problem location of layout. Many of us have been there, it's not uncommon to discover a problem with the track with the introduction of a larger vehicle on the layout...

HTH

 

[aaronoxford77]

There are two very likely independent possibilities for the cause of the problem described:

Limitation of bogie movement, both rotation and pitch, such that in one direction the mechanism cannot adjust to the track curvature. Such limitation can be caused inside the body shell, as well as externally by such as fouling of a coupler on body work or detail limiting movement.
The derailment is only in one direction, is this with respect to the track or the loco?
Does the derailment only occur with either of the A or B cab leading, or is it only in one direction on the layout, whichever cab leads?
What happens if you trial the mechanism with the body removed?

Then there is the track, does the derailment always commence at one location?
If so observe that location very closely.


And then there is 'interaction'
If this loco is the longest six axle model you operate, and all other traction and vehicles are derailment free, then you may be looking at a subtle track alignment problem which just pushes the larger unit 'over the edge'.
You may need to test independent of the layout to see if the loco is problem free on the same radius curve; and if it is then re-lay the track in the problem location of layout. Many of us have been there, it's not uncommon to discover a problem with the track with the introduction of a larger vehicle on the layout...

HTH

Thanks for the response. This is the only locomotive that does it, and it is only one end regardless of the direction of travel, we have many locomotives, and indeed many that are longer than the 66 (70, 9F etc) and we have no problem with others. At first I thought it may be the bogie was over tightened, so I loosened it slightly but nope, wasn't that. So I decided maybe the wipers were causing it, nope wasn't that. I thought maybe it was a wheel out of gauge, nope wasn't that either. Tried swapping the bogies around, but it was the same end with the "good" bogie. Could it possibly be a slight twist in the chassis? I'm literally at a loss.

 

[34C]

Right, so you have done a lot of good 'poking around' to try and sort out cause.

Rather than a 'twist' in the chassis I'd first look for some concealed fouling of a bogie against fixed structure, which produces the same effect as a twist when it is acting. I don't know this model construction at all, not having looked at any N gauge for over a dozen years: but the 66 has some assymetry in its underside, which means the inside end of one bogie is always very close to underside fixed structure; this caused some problems on Bach's OO model. I would want to look at that before diving deeply into construction to determine if there is a built in twist on the chassis.

All the best with it, and when you nail the problem post your findings!

 

[aaronoxford77]

Well folks, I've tried everything and then some! Decided to perform a total strip down and discovered that the frame at 1 end is indeed warped. To add to the problems, the motor then decided to perform what I can only describe as the Dapol dance and completely burnt out. So, the only thing I can do with it is to remove the motor, use it for the time being, as a dummy locomotive, until such time as I can source another chassis and motor. Thanks for the help and, never know, I may get the thing working again when I can get the parts.