Hi,

This involves an analog layout with M track.

My Santa Fe started derailing on one particular switch (points, turnout). Other loks did not. It did not derail on other switches. It had long handled this switch smoothly. Must be the switch. Or the Santa Fe.

So I changed switches three times -- same situation. Hmmm.

So I changed the springs (yes, the correct spring) on the switches, serviced them well, and tried each of them again. Even tried a second new spring on one -- same situation. Hmmm.

Database searching turned up references to F7 loks being notorious detailers. I believed it.

I found one discussion of the importance of the lok wheels being precisely spaced. Checked and tweaked -- and the derailments continued. Hmmm.

Serviced and closely examined the lok and its wheels. Nothing I could see.

Growing desperate, I tightened the new (!) spring controlling the switch, essentially shortening it by three or four loops.

Miracle! The Santa Fe now runs through the turn time after time with no issues. Why that one lok was bedeviled by a slightly slacker (i.e., normal) spring shall remain a mystery. My conclusion is that this one locomotive simply needs an extra-tight spring.

I tell this tale in hopes that SOMEBODY can benefit by it. Altruism aside, truth be told, I'm hoping to amortize the many hours spent in diagnosis over more than one person getting an F7 to run smoothly through turns. Of course, leaving myself open to learning that I have reinvented a round wheel. lol

Smooth running,

Bill