Model Railroader – September 2019

N Scale Insight

22 http://www.ModelRailroader.com

By Jim Kelly

Disassembling N scale diesels

In the 1990s, Kato pioneered

its classic, vertically split-frame

design. Since then, probably

more than 80 percent of the

N scale locomotives made,

regardless of manufacturer,

have followed (in fact, down-

right copied) that approach,

meaning that if you’ve learned

how to work on one of them,

you can work on nearly all.

Why take an engine apart?

I never disassemble a locomo-

tive unless I have to, and then

I go only as far as I must. The

first step is removing the body

shell, and sometimes this is a

considerable challenge. On

most, perhaps all, N scale

engines, you remove the shell

by spreading the sides to dis-

engage them from the nubs on

the frame that secure them.

I usually lay the model on

its back on a piece of foam or a

foam cradle and pull the sides

apart with my thumbnails

while lifting one truck with

my fingers. (This is one of

those rather simple things that

can’t help but sound difficult

when you try to explain it.)

If that doesn’t work, then

I’ll usually insert round

wooden toothpicks to hold the

sides apart while I try prying

at one end of the frame with a

small screwdriver.

That works most

of the time. While

I’m at it, I usually

file those afore-

mentioned nubs

about halfway

down so the job

will be easier the

next time.

Motor contacts.

Usually, when an

engine won’t go,

it’s due to poor

electrical contact

between the light

board or Digital

Command

Control (DCC)

decoder and the motor. One

dead giveaway is that the

lights work but the motor

doesn’t. To fix it, you’ll need

to take the board out and

clean the contact pads.

I do this with the eraser on a

common, ordinary pencil.

If the motor still won’t go,

you may have to bend the

motor leads a bit to get suffi-

cient pressure for good con-

tact. Some decoders have arms

on the sides that reach down

and embrace the motor con-

tacts from each side. You need

to be certain that both motor

contacts are under the arms.

I’ve found it’s not uncommon

for the contact extending up

from the bottom of the motor

to be tucked in improperly.

Next would be to take the

motor out and test it using

DC power and test leads.

(Actually, I’ve never had a

motor fail, although I’ve

burned out several via short

circuits that were entirely my

fault.) To pull the motor,

you’ll have to push in the tabs

that interlock the plastic

motor saddle from one side.

You should be able to test the

motor without removing it

from the saddle.

Should you remove a

motor from its saddle, say to

replace brushes or

solder DCC leads

to the brush caps,

study carefully

how the motor fits

in. Trying to get

it back together

correctly can lead

to madness.

Cleaning trucks.

I’ve ranted in this

column before

about how impor-

tant it is to keep

an N scale layout

clean, especially

in construction

zones. When a

truck starts

thumping, it’s almost always

because a tiny bit of grit or

other foreign material has

gotten into the gears and has

to be cleared out.

To remove the trucks,

carefully loosen the screws

that hold the frame halves

together until the trucks

come out. It doesn’t take

much, and you don’t want to

pull the frame halves com-

pletely apart. The first thing

I do is push the trucks back

and forth on the track to see if

they turn freely. If one doesn’t

roll, I disassemble the truck.

To do this I insert a small

screwdriver in the slot at the

end of the gearbox. Work it

in gently as far as it wants to

go, then carefully pry the

gear box cover off. Remove

the metal clips that retain the

axle ends (they’ve probably

already fallen off ) and pull

out the drivers.

A few words of caution.

Don’t even think about disas-

sembling the trucks on newer

version Kato SD40-2s. The

axle retainers are a unique

design that’s nearly impossi-

ble to get back together.

I wash all the truck parts

in warm water flavored with

liquid dishwashing detergent.

I swish them around briskly

and then begin brushing with

a soft-bristle toothbrush, get-

ting to the visible gear sur-

faces as best I can, turning

the gears with a fingertip, and

brushing some more.

Finally, I rinse the gear-

boxes under running water

and blast them with my air-

brush to dry them out and

hopefully knock out any

debris that might still be in

there. I’ve never actually seen

the culprit that caused the

thumping, but usually it’s

been dislodged by this stage.

To r e a s s e m b l e t h e t r u c k s ,

place the drivers back in their

slots, position the axle retain-

ers, and hold them together

with your fingers while

inserting them into the truck

frame. It’s easiest to insert

one end, then work your way

to the other.

Another word of caution:

Don’t assume these axle

retainers are symmetrical

when it comes to six-axle

trucks. On InterMountain

SD40T-2 tunnel motors, I

made that assumption, but I

was wrong. I learned I need

to measure.

Good luck, and keep ’em

running.

Jim Kelly took apart this Atlas N scale SD26. Two plastic

bushings separate the halves electrically. Metal screws pass

through these bushings and engage plastic nuts on the other

side to hold the halves together. Bill Zuback photo

Truck mounting points

Plastic bushings

I’VE RANTED IN

THIS COLUMN

BEFORE ABOUT

HOW IMPOR-

TANT IT IS TO

KEEP AN N

SCALE LAYOUT

CLEAN, ESPE-

CIALLY IN

CONSTRUCTION

ZONES. – JIM