Smaller locos derailing

[Dobson]

I have a bunch of smaller postwar locos with single axels in the front (675 and similar). They always seem to derail with the smaller front wheel around turns and in switches.

Anyone have any solves for this? A new spring under the truck? Don't run them (a solve but not preferred)

Thank you for your help

[lionelsoni]

Those locomotives suffer from an incorrect steering geometry, which causes the pilot truck to oversteer and often derail on curves--the sharper the curve, the greater the effect..  If you put the locomotive on an O27 curve, you may be able to see that the pilot wheels are not parallel to the rails, but angled toward the inside of the curve.

The pilot truck should have a longer tongue and should pivot around a point midway between the pilot-truck axle and the middle-driver axle, which is about where the motor's front crossmember is located.  You may get along with a stronger spring or more weight on the truck or both; but, if you're willing, the real cure is to splice on a longer truck tongue and to create a new pivot at the correct location, as by drilling and tapping the crossmember.

[BigAl 956]

The truck spring is the first thing I would replace. The pilot truck is pushed down with a small spring. Often this spring is worn out, broken, or missing. The spring is literally a 10 cent part. Unless you already have replaced it I would change it out with a new one even if it seems OK.

I also recommend staying away from O27 track if that is what you are using. O27 turns are so sharp this type of derailment often occurs. If you use O27 make a new years resolution to move to standard O track. Your layout will thank you for it.

[TRAINCAT]

The other thing with these to check is actual wheel gauge. Some are too wide and ride up over the rail in curves. Remove the truck and set it on the rails and see where you are with width.
Roger