Why repower? To improve running characteristics to suit your needs and desires. These may include changing speed, increasing drawbar pull, improving appearance, replacing poor components or drivers with the correct size. But before running off in the wrong direction, you must EXAMINE AND ANALYZE the starting conditions very thoroughly and then decide how to achieve the desired results.

The ideal goal should be an optimum coordination among the motor, gear train, driver size and range of control. All locomotives have a maximum speed at 12v and a minimum startup voltage with or without a load. A common example is a switcher that hits over 100 SMPH at 12v and starts at 4v. This gives an operating range of 8v. Common power packs have a throttle knob rotation of 270 ° and a possible maximum of 16v. Only half the rotation is usable for speeds from 0-100 SMPH. If the top speed of the switcher is 25 SMPH only 1/4 of the half turn is usable for 1/8 of the full rotation or about 33 °. This yields very touchy control. Repowering for a top speed of 25 SMPH at 12v will raise the control range to 1/2 turn, permitting finer adjustment. This comparison applies to all types of powerpacks including "digital". Repowering is suggested.

Probably difficult to locate, a replacement motor, at 1/4 the original RPM, would help at the high end, but might raise the starting voltage and degrade low speed operation with torque loss and cogging. Only a good marriage of gear train and motor may suffice. See MOTOR EVALUATION for some comparisons.

Another possible reason for repowering is poor drawbar pull. Using a SENSITIVE AMMETER, determine whether drivers slip at a current less than the motors continuous rating and why. Often auxiliary truck springs tend to reduce weight on drivers. Removing a few coils or bending wire springs, to the point where trucks still stay on the track safely, can help. Maybe adding some weight and balancing are what is needed. Balancing is necessary to assure that all drivers have nearly equal and sufficient weight on them. Mounting a higher torque motor will only aggravate the situation unless sufficient weight is added. For more details see: WEIGHTING LOCOS.

If noise reduction is your goal, find the source. Gear trains generally contribute far more vibration noise than motors. Excess play in bearings, including motors, and gear slop or tight mesh can cause vibration, clicks and squeals. Loose shells or parts may amplify any vibration audibly. Soft or heavy masses tend to absorb vibrations.

Determine the frequencies of the noises. Very high pitches are very often caused by motor brushes, poor worm mesh, misaligned or dry bearings on higher RPM shafts. Motors can be isolated to determine their culpability. Lower frequencies may be generated by shaft endplay. Bronze shim thrust washers can reduce this in most cases excepting can motors. A MOTOR TUNE-UP and proper lubrication can drastically reduce noise level.

Do not overlook your power source. Pulses of any type cause vibration. Various pulse rates can effect specific motors or mechanisms quite differently. DCC is no exception. Even those far above audible frequencies can produce lower mechanical vibration frequencies in devices. Vibration also produces heat, since heat is a molecular vibration.

Again I repeat, know what you have, why it requires change, where and how to change it and with what. A thorough ANALYSIS can save a lot of wasted effort.

Several options may be available: use a KIT OR DEVICE; REMOTOR , REGEAR or a combination. Is adding a FLYWHEEL worth the effort? Choice is dependent on several factors, most importantly, the SKILLS, TOOLS and cost required. The job may require only a screw driver and some soldering or it could necessitate a full machine shop. Before opting, a good estimate of results could eliminate costly mistakes. Not every case can be ideally resolved with the limited variety of devices, motors and gears available. A clear perception of all power train functions and characteristics is very beneficial. These will be covered as thoroughly and explicitly as possible in related sections to help avoid the pitfalls of hype and misguided info through knowledge.

Thorough LOCO TESTING is absolutely necessary from start to finish.

Know and analyze the original SPEED , motor, gear train, weight, current and other running characteristics before ripping everything apart. Don't fix something that doesn't need fixing.

Examine and measure the cavity available for new installation to help determine what may fit. Measure the inside of the shell including any mounting bars. Often in brass diesels and electrics, the desired can motor will not squeeze past these, requiring surgery. Often exterior details have lugs, wires and solder joints that require cleanup to provide clearance. There may be internal bracing as at the front end of a fire box or at cab ends. Examine the frame for required mounting surfaces, driver clearance and any possible new screw holes.

If you can't find gear info, count teeth. CALCULATE motor RPM from track speed. Measure drivers in inches and scale inches. Many brass locos have drivers about one inch undersize to improve appearance and to allow for over scale flanges. The MDC PRR E-6 Atlantic has 75 in. drivers instead of 80 and the PRR consolidation and G-5 have 65 in instead of 62 and 69 respectively. Find the weight on drivers. Measure axle center to frame mounting surface, if regearing is suggested.

Keep intelligible notes. It may be some time before you find and acquire everything needed. Use your database and drawing programs.

Look at these, if you don't know


or how:

If you know all the answers, skip the subsections and dig right in. However you may be missing something, if only the chance to DISPUTE MY FINDINGS.

Decide on your goal and determine how to get there and what is needed, including ---tools. Again, look at the associated sections before you leap. When you feel sure, do it. It's fun and rewarding.

First look around for some easy solution that may not require extensive knowledge or tools. In some cases speeds are given and most provide instructions. Success with an easier project may build confidence.

CAVEAT EMPTOR: Over the years there have been many devices with wild claims for performance improvement. Most were not attempts at fraud, but were derived from the developer's lack of knowledge and ability. These include centrifugal clutches, "super" flywheels and motors and superior slow speed devices. Simply, thoroughly analyze the hype before buying using the information found here.

Recently, One device provides a new flywheel/worm for switchers and touts tremendously improved slow speed operation. Since all operations are still limited to the lower 1/4 of the motor and throttle range, no improvement is gained in control. The "flywheel" radius of gyration and the angular velocity are too small to provide enough momentum for any useful purpose.

A second conversion for road locomotives suffers the same flywheel problems, but aggravates the condition by replacing the motor with one of considerably less mousepower and one size fits all.

In larger scales NorthWest Short Line (NWSL) offers the Magic Carpet series of mostly below the floor power units. These are essentially truck axle mounted gear-motors that can be used singly or in multiples for traction to diesels. A No. 1 Gauge power truck is also available. A wide selection of wheels is available.

In HO they also offer the PDT (Pretty Darned Tiny) series, which are actually small self contained power trucks. A variety of sizes, wheel bases and diameters are available. Mounting may require some surgery in the floor area.

Tenshodo offers the SPUD (Self Propelled Under the floor Drive units?) of a similar but generally smaller type. Mainly designed for traction, they are relatively easy to mount. A fairly wide selection of wheel bases and diameters are available.

Precision Scale has a very similar, VARIABLE WHEELBASE UNIT.

NWSL offers the FLEA , which is basically a single axle gear-motor drive to which additional geared axle may be added.

ERNST offers regear kits for Athearn to reduce speed. They a little noisier but perform well. The only problem is determining where the new gears go.

Many drop-in REGEAR KITS kits are available from NWSL for Roundhouse (MDC), Rivarossi (AHM) and some brass. Caution: Some require gear pulling and pressing and even driver quartering, covered in another section.

Mantua has RETROFIT kits and parts to replace the PM-1 motor with a larger and slower motor in some of their locos. As parts, they also offer gear boxes used on loggers and atlantics, which can be modified to accept other gears.

HOBBYTOWN of Boston offers a variety of diesel chassis for Athearn and others.

FRONT RANGE offered a variety of diesel chassis for Athearn, MANTUA (TYCO) and others.

There may be others, including some that I can not recommend, but the above HO have been tried and tested.



Once you have an idea where you would like to go, gather as much info as possible on sources, parameters, availability and cost on what you may need. Many items are advertised or found in catalogues and parts lists. Suggestions are included in subtopics. Analyze things very carefully. Mistakes can be expensive.

Look for EXAMPLES in articles, from local experts, at NMRA meets etc.. Be sure to analyze to adapt and improve, if possible. Make sketches and dimensioned scale drawings if possible. It's easier to erase a paper or computer drawing than to undo surgery. Always consider the alternatives, REMOTOR , REGEAR or both.

Know the METHODS AND TOOLS required to accomplish the job.

To end the tirade, "Make haste slowly". Have at it.

Good Luck!


Authored on the AMITHLON AMIGA


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