Bachmann Ewes 66 050

[Lurcher1]

This loco on a circular track one of the wheels usually jumps the track, it can be any of the wheels, I also have a set of points that it derails every time it passes over, I have three other Bachmann and three Hornby locos, that pass over these points with no problems, thinking of sending it to Bachmann to see if it can be fixed,
I am a club member and a couple of experienced members have looked at the points and said they are okay.
Any ideas what could be causing this loco being a serial derailer?

[Len]

What size curves are you using? While it may handle it at low speed, the wheelbase on a Class 66 loco is not going to be happy on R1 curves or turnouts.

Len

[Lurcher1]

First radius it's on a 6ft x4ft board

[Lurcher1]

Yeah have just tried it on the second radius with no problems, I usually run my passengers on the second radius and my goods on the other, so I was perceiving with it, thought it would be okay, but it looks like it will have to be the second radius  from now on.