Troubleshooting vintage O gauge locomotives

After many years of repairing Lionel and other makes of classic toy trains, I’ve found that most locomotive failures are electrical in nature. Surprisingly few are the result of mechanical shortcomings.

For electricity from the transformer to do its work, it must be properly directed to the two major components – the motor and the reversing mechanism (commonly called an E-unit). The thousands of Lionel trains made during the 20th century are relatively simple machines, and the problems they develop usually aren’t difficult to ascertain and successfully repair.

In this article, I’ll address postwar and early modern-era Lionel locomotives powered by open frame (“Pullmor”) motors. Modern locomotives with sealed can-type motors and complex circuit boards usually require the services of a qualified technician. However, some of the following suggestions, such as tracing loose wires and adding proper lubrication, apply to these units as well. Let’s get started!

Open circuits

We’ll look at the most obvious difficulty first. If there is power to the track (use a test light to be sure) and your engine is stone cold dead – no lights, no hum from the E-unit, and not a spark of life from the motor – the problem is almost certainly an open circuit. This means electricity isn’t going where it should. Look for the following conditions.

Broken or loose wire. At right is a diagram of the wiring for a typical locomotive. Two wires from the reverse unit connect to the brushes. One is attached to the field of the motor, and the other connects to the pickup roller assembly. Examine each wire to determine if there is a loose connection. Most locomotives have an additional wire or wires for the headlight and/or cab light, and many diesels have a built-in horn circuit, but these wires are not involved in making the motor run. If the headlight doesn’t work, and you know the bulb is not burned out, look for a loose or broken wire to the pickup roller assembly. Also check the ground connection from the field.

Wire caught between frame and shell. This can occur when a locomotive is reassembled after servicing, and may not be as obvious as in this photo. The result is a short circuit if the insulation is cracked or torn and allows the core of the wire to touch the metal frame. The wire may even be broken inside its insulation. Check it for continuity, replace if necessary, and tuck it well inside the engine’s interior.

Distorted finger in reverse unit. Reverse units are fairly dependable devices, but these delicate parts lose their tension over time, and corrosion may weaken them. You may be able to bend a loose finger enough to restore contact. Replacement reverse units are available from your local hobby retailer or through nationwide parts dealers.

Brushes don’t contact the commutator. Sometimes dirt will cause a brush to bind in the metal brush holder. Try cleaning both the brush and the holder with a mild degreasing agent. A word of caution – be sure to avoid products such as acetone that will harm plastic. Also, the spring that presses the brush against the commutator may become dislodged or weakened.

Soldered joints on armature are broken. The arrow points to one of the soldered connections that can come loose. Check the entire armature for proper conductivity, as described under the “Loss of power” heading later in this article. You can probably resolder any loose wire, but sometimes an armature must be completely rewound, a job best left to a qualified repair shop.

Short circuits

If the transformer overload light comes on after you’ve advanced the throttle or the circuit breaker trips and cuts off power, there is a short circuit. What’s a short circuit, you ask? Any circuit in which the electricity can return to the opposite pole of the power source without passing through the device it is meant to activate. Electricity will always follow the path of least resistance, bypassing a lamp or motor when another route exists. Some of the most common causes for a short circuit are as follows.

Loose wire contacting frame. Be it the result of a failed solder joint or an excessive tug when removing a part, a loose wire touching the frame or another wire connection point will cause a short circuit. Determine where it belongs (refer to the wiring schematic on the previous page) and reattach it. This probably is the most common short circuit and the easiest to remedy.

Frayed wire contacting part. The insulation surrounding wires used to connect vintage toy train components, such as this 70-year-old reverse unit, can easily crack or dry out. In this case, the bare wire can contact with any number of locomotive parts to cause a short circuit. Wrap the offending wires with electrical tape, or replace them entirely.

Exposed headlight wire. While this problem isn’t as easy to detect, it is common on older locomotives with cloth insulation around the wires. A short circuit can occur when an exposed wire touches a metal part of the socket or other components along the wire’s path between headlight and the pickup roller. It’s best to replace any wire with worn or frayed cloth insulation.

Also, sometimes the washer inside the socket becomes bent or otherwise distorted, causing a short circuit. It should be replaced if you can’t bend it back into shape without breaking it.

Bent pickup roller. Through improper storage, rough handling, or a severe derailment, the pickup roller may become bent or dislodged to the point that it touches the frame or the back of a wheel. This misalignment is another hard-to-find, yet not uncommon source of a locomotive short circuit. If it can’t be straightened using needlenose pliers, replacement assemblies for most locomotives, even very early ones like this 90-year-old boxcab engine, are available from parts suppliers.

Loss of power

Your locomotive may light up and move forward sluggishly, yet it seems to lack power. It may run with a jerky motion, stall completely at low voltage, or be unable to attain normal speeds. To operate properly, the motor must receive an unimpeded amount of electricity, and there must be nothing that causes the mechanism to bind or to develop unnecessary friction. Let’s first examine the electrical causes for this type of failure before we explore other possible mechanical issues.

Improper lubrication. Using the incorrect type or an excessive amount of lubrication can interfere with electrical transmission. When applying lightweight oil or grease, be sure none of it comes in contact with the brushes or commutator. Also be sure the wheels are clean and free from oil or grease. A little bit of lube goes a long way.

Dirty drum. Inspect the drum of the reverse unit for dirt or corrosion. It doesn’t take much to impede the flow of electricity. You can clean dirt from the metal parts with a mild degreaser or solvent on a cotton swab. Never use cleaning solutions or products that will harm the plastic drum, such as acetone.

Clogged commutator. Dirty brushes or a commutator that’s clogged with residue from the brushes can cause stalling and jerky operation. Clean the commutator by rubbing it with a pencil eraser. Also use a miniature screwdriver blade to clear the slots between the commutator segment. Be careful not to scratch the surfaces or disturb any of the wire windings.

Weak brush holder tension. Check the spring tension in the brush holders. After years of use, the spring tension that keeps the brushes in contact with the commutator can weaken. Insufficient pressure may cause sparking and uneven current flow. Quite often, when a locomotive performs better or runs faster in one direction than it does in the other, uneven brush spring tension is likely the reason.

Although you can attempt to adjust the tension of these springs, it’s probably best to replace this key component.

Short circuit at commutator.  Set a test meter to the ohms position, clamp one lead on the armature shaft, and touch the other lead to each of the three commutator segments, one at a time. The meter should indicate “INF” (infinity)—in other words, it should not move, indicating that there is no electrical connection (a short circuit) between the commutator and the shaft.

If you don’t have a meter, use the two wires from a transformer to test for this condition, with the throttle set at about 12 volts. There should be no sign of sparking. If there is, you can obtain replacement armatures from parts suppliers.

Open circuit at commutator. Touch one lead from the test meter to one of the segments of the commutator, and the other lead to an adjacent segment. The meter should register little or no resistance (zero or close to it). Repeat the test for the third segment.

In the absence of a meter, use two wires from a transformer with the throttle set at about 12 volts. There should be a strong spark at all three segments. If there isn’t and you can’t find any broken wires, contact a qualified repair shop or obtain a replacement armature from a parts supplier.

Friction and binding

Following are the most common mechanical problems that interfere with smooth operation. The foremost cause of poor performance is friction from lack of lubrication. Consult the instruction sheet that comes with each locomotive for the proper application of oil and grease, and lubricate very sparingly. Too much oil or grease attracts dirt and hastens the reoccurrence of these problems.

If you don’t have an instruction sheet, the following general guidelines apply.

Dry rods. Place a drop of oil on all moving parts of a steam locomotive valve gear and side rods. Make sure no oil migrates to the wheel treads. Wipe everything with a soft absorbent cloth, such as an old t-shirt, when you finish.

Binding axles and pivot points. Oil all axle bearings sparingly, including those on the pilot and trailing trucks. Also add the smallest drop of oil on each side of each pickup roller. Excess oil here will find its way onto the middle rail. Also oil the pivot points on leading and trailing trucks.

Worn armature shaft. On locomotives where the armature shaft protrudes, place a tiny dab of grease on the shaft. The bearing in which the shaft rotates can become worn, causing the armature to wobble. Replacing the bearing is normally a job for a repair shop.

Dry gears. Even just a dab of lightweight grease (use the proper formulation for plastic or metal gears) applied to the gears can improve performance. It isn’t necessary to coat the entire perimeter of each gear. The grease will migrate as the wheels turn under operation.

Dry shaft. On vertical motors with a small hole between the brushes, add a drop of oil. These motors have a ball bearing at the top of the armature shaft that should be lubricated very sparingly. Excess oil here will travel to the commutator and brushes.

Binding side rods or valve gear. If a steam locomotive seems to hesitate slightly with each revolution of the wheels, the most common cause is a bent rod or incorrectly installed rod screw. Remove the rods and valve gear, and test the locomotive on the track. If the problem has disappeared, reinstall the rods one piece at a time and test after each one is attached. When the problem reappears, the last piece you installed is the source of the binding.

Mystery metal parts. Examine the gears and wheels for foreign objects. This problem most often occurs with Lionel locomotives equipped with Magne-Traction.

Worn or wobbly gears. Finally, inspect the mechanism for gears that are worn or loose on their shafts. This problem is especially prevalent on Lionel’s postwar Alco diesel locomotives. Gear replacement requires specialized tools and is best left to a repair shop