Locomotive Motor Tips
Prior To Installing
DCC Decoders

This all started because we had a clinic on decoder installations planned for our Nottawasaga Model Railroad Club (NMR) members. 

Fellow club member, Bill Payne, did a clinic on correct soldering techniques and followed that with a clinic on servicing DC motors prior to decoder installations. 

We have several older Athearn locomotives at the club that will be used for demonstration purposes to show how to "hard wire" in a decoder. 

The first rule is "if the engine doesn't run well on DC, it's not going to run any better on DCC"

The first step is to get the engine working better to begin with. So here are Bill's locomotive motor tips and his Engine Servicing 101 Course. 

How engines get power from the track
and how to make them move

Some terms to understand:

  • Wheels: Pick up voltage from the track. May have wipers or shoes from chassis rubbing on track.
  • Wipers: May rub on tread or on back of wheel. Lighted cars and tenders may have wipers on axles.
  • Wires: Carry voltage from the wipers to motors.
  • Motor: Converts voltage to rotating motion. 
  • Universals: Allow minor misalignment and movement between motor and gearbox.
  • Gears/Gearbox: Provides a means of changing rotation of motor 90° and gear reduction (depending on gear type). 
  • Axles: Provide a means of connecting final gear (in gear reduction) to wheels.
  • Bearing Blocks: Provide a means to seat and lubricate axles to reduce friction between axle and gear housing.
  • Thrust Washers: Spacing washers often found next to bearing blocks to reduce horizontal movement.
  • Fly Wheels: Keep the motor rotation going over dead spots (momentum) and add weight.
  • Wheels Again!: Transmit rotating motion to track to make the locomotive move.

A few locomotive motor tips: Older Athearn locomotives have sintered wheels. This is a process of making the metal. The metal is actually porous and has oil in it. The recommendation is to replace the older wheels with steel ones. These can be obtained from Northwest Shortline or through a hobby shop. 

Prototype railroads use sand to help adhesion when starting, stopping or on grades to overcome slippage. We can't do that with our models. There is a product called Snot that acts like a traction tire. I've never used it. I'd rather double head locomotives. That's easy to do with DCC.

 However, steel wheels provide better pickup and don't pick up as much crud from dirty track. The wheels are a press fit on the plastic axle with the gear.  

In our experience, some Proto 2000 axles were faulty and split. This caused a cogging effect as the gear slipped. Replacements are available. 

Often you can use axles from Athearn locomotives because the tooling was the same.  

You can often buy some used, old Athearn locomotives at train shows and auctions and salvage parts from them such as the axles, motor springs and the carbon rods (brushes) that press on the commutator.

Motor Types

You can find information on the Internet. That's where Bill Payne found this. To help you avoid hunting for it, here's what he found: Most motors used for model trains are skew wound, even Athearn open frame motors. Open frame means you can look inside the motor and see the windings and other parts.

A can motor is constructed so that you can't see inside.  

An exception to skew wound are the older Pitmann motors that Bowser used in steam engines. Some brass engines also used similar types. 

If you rotate the shaft with your fingers you can feel the hesitation as the magnets in the motor pull at the windings. 

A skewing of the armature helps to overcome this cogging effect to provide for smoother starts and stops.

Should you want to replace an open frame motor in an older Athearn, good motors are made by Cannon, Buehler (for Athearn Genesis, Stewart, Atlas and Overland. Micromark has a Mashima clone). 

Another make is Mabuchi. These are mainly desinged for slot and R/C cars.

Diesel replacement motors should typically be in the 10-12,000 rpm range for diesels with 12:1 or 14:1 gear ratios. Steam engines may require motors in the 6000 to 8000 rpm range.

Incidentally, steam engines use larger gear reductions because the driving wheels are much larger. Diesels generally have 40, 42 or 44 inch wheels. 

Be careful when replacing wheels sets that you get the correct size otherwise your coupler height may be off or the wheels will bind against the chassis.

Axles on can motors are often 2mm. The old Athearn open frame motors have a much larger shaft. You will probably need to change the universal couplings to go from the new motor to the gear tower that turns the axles. 

A Vernier caliper can be used to check the sizes. If you are unsure the Northwest Shortline catalog is extensive and they, or a good hobby store, can help you get the right couplings and wheel sets.

Some modellers have used fuel lines for model airplanes as a way to connect the shafts. This can cause slippage and wobbling. Correct universals are a better solution.

Motors can be mounted with silicone sealant or you can make new seats from styrene. The motor has to be insulated from the chassis for decoder installations. That's another story.

More about motor types

The most common types for model trains are the conventional iron core motors and newer coreless motors. The can motor is made from formed steel. 

They are known as permanent magnet DC motors and have an armature wound on a core of iron. They are relatively cheap.  In larger scales such as O scale the motors are generally iron core can motors. 

A coreless motor doesn't have an iron core. Thw windings are held together by plastic. That's why you have to be careful not to overheat a coreless motor because the plastic can melt.

Coreless motors are more efficient than cored motors but you sacrifice the heat sinking ability. Coreless motos can be found in smaller scales. If overloaded with current they will fall apart internally.

The number of magnetic "poles" also affects how the motor operates. Can motors generally have 3, 5 or 7 poles. The more poles, the smoother they'll operate. More poles are slightly less efficient. 

R/C cars often have only 3 poles because low speed isn't usually a factor.

More poles decrease the room for windings. Larger scale trains usually have 5 pole motors. LGB G-scale engines sometimes have 7 poles for smoother operation. 

If a motor is "skew wound" like the Athearn motors, you will see gaps between the armature poles and they are slanted compared to the fixed poles in other motors.

As mentioned earlier, this reduces cogging and improves low speed performance.  You pay for what you want!

Reference: www.trainweb.org/girr/tips/tips5/motor_tips.html.

Bill Payne's Diesel Locomotive
Service Guide 101

  • Poor Performance: Look for dirt, dust, hair, crud. Check wheel treads and between wipers and the back of wheels.
  • Sparking/Smoke: Too much oil and/or grease.
  • Tight/Worn: Broken or missing parts. Check carbon brushes and springs.
  • Alignment: Wheels may be in gauge but misaligned front to back. Universals may be misaligned.

Listen to your engine and make notes. Locomotives often run better in one direction than the other and will be noisier in one direction. 

Check slack around thrust washers. Make sure wheel treads are clean. 

Some modellers use a Dremel brush while the engine is running on its back. Others, for DC, can use the Kadee wire brush. Alcohol is the best cleaner. Use 70% isopropyl alcohol.

Smoke can also be caused by a motor overheating due to tight parts or other problems. Remove the couplings so you can run the motor free of connections to make sure it's not the motor.

Listen for clicking in the drive train. This can be a bit of flash on a gear or even a speck of metallic ballast that's been picked up. Commercial ballast is usually free of magnetic debris, but if you used real dirt it could have iron in it, especially if it's that lovely rust colour!

If the locomotive is jerky there could be a tight part. A steam engine could have binding in the siderods. A diesel could have less than enough play in the drive train. Jerkiness can also be caused by poor electrical contact.

Check the wipers. On Athearn locomotives, check the seating between the trucks and the chassis. The electrical pickup relies on a mechanical connection at this point. Polish around the king pin that the truck swivels on and the surfaces where they make contact.

If speed is inconsistent it may be a bad "u" joint or loose tubing if that has been used for coupling to the driveshaft.

Dead crossing unpowered switch frog: Turn engine over and check coninuity with a meter. Are all wheels picking up? (Wiper shoes can be added, Taurus Products make track slider pickups for HO scale.)

Commutator (open frame motors): Clean with alcohol on a "Q" tip. (Any loose fibres will burn off). Gently clean out gaps beside the poles with a needle or tip of an X-Acto blade.  Use wet/dry emery paper to polish the commutator. Do not use sandpaper. Check for wear. 

Is the carbon brush still intact or is it the spring that is making contact and wearing down the commutator?  If you think there's a dead spot use a meter to check continuity.

If you still have it, check the owner's manual for frequency of lubrication. It depends on how much running the engine does, layout dustiness, or how long the engine has been on the shelf.

Some modellers make it a habit to do this once a year. I'm not that organized. I usually wait until a locomotive is acting up or I need to do some other work on it. I do clean the wheels quite often.

A very little oil goes a long way. Most modellers overdo it. if you don't have a syringe type dispenser such as the ones Labelle makes, put a drop of oil on a scrap piece of plastic and dip a needle or pin in it to pick up a tiny drop. 

I use Labelle 108 lubricating oil and Labelle 102 lubricating grease. There are other brands.

Oil around the shaft where it enters the motor. Keep the oil off the commutator otherwise you're going to get a lot of smoke burning it off. 

Apply also to the bushings. if there's an oily film on the gears you don't need more grease. If there's a lot, wipe it off. 

Again, alcohol can be used to clean the gears before applying new grease.

it's not necessary to disassemble the locomotive. A drop of grease on the axle gear will be distributed throughout the drivetrain as the engine runs.

Run it in a cradle if you have one, on its back, or on the layout.

OK, now that your engine is performing better you can move on to install a decoder.  Many of the newer DC locomotives now have drop-in decoders that makes installation easy. You just plug them into the existing electronic board.

However, if you have old Athearn or Atlas engines like I have, you will probably need to hard wire them or install plugs. You can see what I did for two installations by using the links below. 

I'll also post a page after we do the decoder installation clinic at our club.

Our club layout and mine are HO scale. Most of the above also applies to other scales. I don't have much experience with N scale locomotives. 

If you're into O scale trains you might also like to check out  O scale maintenance.

I hope you've found these locomotive-motor-tips useful.

Return from "locomotive-motor-tips" to DCC overview.

Go to decoder installation in an Athearn locomotive.

Go to decoder installation in an Atlas RS-3 locomotive.

Go to brass engine decoder installation in an Alco RS-18.

Go to phosphor bronze wire for all wheel pickup.

Return from "locomotive-motor-tips" to my Home Page.

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