How many times have you retired a favorite boxcar or gondola to the shelf because the *&$% thing won't stay on the track and you can't figure out why?  I'm not promising you that this article will address all your problems, but I will assure you that the following common maintenance actions might solve some of them.

CLEAN THE WHEELS!!  I have scraped dirt, hair, grease, Christmas tree tinsel, and thread off wheels that was built up so heavily that rolling around any curve caused the truck to ride up over the rail. 

CHECK THAT ALL WHEELS TOUCH THE TRACK.  Trucks can become twisted slightly causing one of the wheels not to touch the track.  This can be part of your problem.  You'll have to twist the truck until it's back in alignment.

LOOSE SIDE FRAMES.  I've found that loose staking on the truck side frames may cause the car to derail especially when negotiating an O-22 switch.  The sloppy side frames allow the wheel to move from side to side-creating trucks that are out of gauge.  Use a pair of pliers to tighten the stakes and also to bend the side frames so they are perpendicular to the axles.

CHECK THE GAUGE.  It seems that front trucks on locomotives do become misaligned and it's not always obvious.  These wheels are pressed on the axle and are not supposed to move.  However, a previous owner may have accidentally changed the gauging.  We all know that you would never do that, don't we?  Gently tap the axle with a small hammer until the distance between the wheels is correct.  Use a truck you know is good or your locomotive as a guide for the spacing.

WEAK SPRINGS.  The front and rear trucks on toy locomotives are there to make the unit anatomically correct.  They don't help guide the front of the locomotive around curves or help distribute the load as on the real behemoths.  They will bounce around and come off the track just to cause you misery.  Check the springs that help keep the wheels pressed to the track.  If they're weak or you're not sure, replace them. 

LIGHT CARS.  If you like to run long consists, and most of us do, then you may experience problems with cars derailing on the curves.  There are two ways to ameliorate the problem: move the car toward the rear of the train, or add weight inside the car.  As an example, the tender with the 1615 switcher would be difficult to relocate so you'll need to install a 6 ounce lead weight to the middle of the frame.  Moving the lightweight cars toward the rear of the train will often solve your derailing problem.  Many of the newer cars have plastic trucks and frames and consequently don't stay on the curves well if there are heavy cars behind it. 

MAINTAIN THE TRUCKS.  Make sure the wheels roll freely.  You've heard the term 'rolling stock', haven't you?  Well we don't want you to have dragging stock, so clean and oil those trucks.  You may have to remove and disassemble the trucks to adequately rid them of old grease and corrosion on the axles.  Once everything is clean, lubricate the axles at each wheel with lightweight oil.  Don't use grease, it will attract dirt and cause you future anxiety.

If you still have problems with derailments after trying the solutions suggested above, then look to your track as the possible culprit.  O-27 track is especially vulnerable to bends and twists that cause misalignment.  The dead give away is if the derailment always occurs at the same area on the track.  Who knows?  Derailments happen.