Jinty polarity puzzle

[Silurian]

I’ve recently been working to revive some Triang Jinties. I have three of them and a diesel shunter. All the chassis are visually identical except that one of them has the later incarnation to provide for a smoke unit (although it doesn’t actually have a smoke generator) . All run well, but one of them runs in the opposite direction to the others. I can fix it by swapping the motor polarity, but I am loathe to do that without understanding why it has happened.  The chassis are isolated on the same side. The one which runs “backwards” is not the unique smoke generator chassis. Any thoughts?

[t-b-g]

The magnet in the motor may be installed upside down or may have been taken out and put back in wrongly sometime.

 

I had the same problem with a loco a while ago and taking the magnet out and turning it the other way up cured it.

 

Good luck!

 

 

Edited May 6, 2020 by t-b-g

[john new]

Agree with t-b-g, reversed magnet. Had same problem with a re-magged H Dublo 3-rail loco that had been done with backwards poles.  After I got it re-done the correct way round it was fine.

 

Edited May 6, 2020 by john new