Building Engines and rolling stock cars: construction tips

This document describes how to build engine and crank cars, and shows details of parts, approximate part costs and suppliers.   A typical engine or drive motor car will cost less than $300 to construct; a passive car less than $100.  

The picture below shows my “original engine” yellow coal car design which pushes a passive orange engine and pulls passive passenger cars.  The key to low cost construction is using available 24-36 V 350-500 watt scooter motors and motor controllers, and using lawnmower wheels instead of premade metal flanged wheels.  This train is remotely controlled by an adult operator using a simple car door opener key fob with 100 foot range.   A “new engine” design is also described that allows a 200 lb adult to sit on the engine and drive the train (assumes filling pvc tracks with sand for more rigidity, which is not necessary if only small children ride the train).



Making flanged engine drive wheels train wheels:

A 6 inch wheel would use a 7 inch cutoff wheel to create the ½ inch flange.  Larger flanges (i.e. 7 inch flanges for drive wheels to be described below) can be cut with a band or jig, saw rather than hole saw.  Drive wheels do not rotate on their axels; they are attached firmly to the axel to drive or rotate the axel.  The usual method is to use a drive wheel hub.  I could not find inexpensive wheel hubs for ½ diameter axels, so made wheel hubs from inexpensive 4.5 inch diameter V belt Chicago pulleys.   See pictures below.

Drill through holes through the pulley, polypropylene flange and lawn mover wheel to create a train drive wheel. 


The wheel connects to the D shaped axel via an allen screw.  Pulleys and D axels can be bought on line from McMaster Carr (see parts list).


Original engine construction tips:


In my original train, the coal car was the motor drive pushing the passive engine .  The passive engine uses the same 2 truck design as caboose; the 2 large white drive wheels are for show and do not contact the tracks.  The motor driven drive wheels are in the rear truck of the coal car above.  This “drive truck” uses 6 inch lawn mower wheels instead of roller skate wheels.  These “drive” wheels have to be solidly attached to axels via wheel hubs, with axels supported and attached to the truck frame by wheel bearings.    I could not find inexpensive wheel hubs for ½ inch axels, so I constructed them from inexpensive zinc pulleys.  The pulley also allows driving a second axel using a pulley belt as shown below (4 wheel drive).   The pulley has an allen set screw that can grab the axel. A  “drive train wheel” can be created by drilling through the relatively soft zinc pulley, and bolting a 7 inch diameter polyprophyline disc  flange and  lawn mower replacement wheel to the pulley.  With 8 inch wide tracks, there is precious enough space to fit the motor.  Note that the 500  watt, 36 volt razor scooter  motor I used was discontinued.  Many replacements exist (see parts list).  However, make sure the motor you choose fits in this confined space; and is less than dimension E.  I now use 24 volt, 250 to 500 watt motors.

This drive truck mounts under the decking of the rear of the “coal car” shown in the picture above.  The coal car is filled with weights (3, 12 V heavy lead acid batteries, plus cinder blocks) for traction.  Without a lot of weight, the traction wheels will slip.   This problem does not exist in the “new engine” design, where the adult driving the engine sits over the drive wheels to provide traction; shown later in this document.

Dimensions:  a = 3.5 in.     b= 9.75 in.   e=    4.5 in.   c=v belt tension pulley (1.5 in diameter) 

Crank engine and Thomas “new motor engine” design construction tips

Compared to my original engine, this design uses a wider platform that is big enough for adults to sit on.  It also  places the chain drives in the center away from little fingers (original design has chain somewhat exposed).   The weight of an adult driver, sitting over the drive wheels, eliminates the need for adding weight for traction.  Because the 6 inch wheels are rated for only 35-50 lbs each, I used 6 wheels to support me, the car and batteries (I weigh 200 lbs).   The middle passive wheels can be eliminated if you are a lighter weight adult.   

To make a hand crank engine, cut down a bike to preserve the pedal and crank gear, and back bike wheel supports.  Mount this on the deck so that the back wheel supports are bolted to a 2 by 4 block of wood to allow movement to adjust the chain tension.   



Dimensions:    a=10.25 inches inner width,    b=  distance between drive wheel axels 16 inches                c=  length of 2 by 4 frame 34 inches    d=   distance between flanges is 6 7/8 inches

The new engine uses the same wheel and axel design as the “original” engine.  However, the 12 inch long axels are supported by the McMaster Carr wheel bearing on the outside of the wheels, rather than between the wheels (shown in the next picture). Note in the picture below, a crank car was converted to a motorized engine. 

The same McMaster Carr wheel bearings as in the original engine were used, now mounted below the wood frame skeleton. The motor used here is a 350 watt, 24 volt gear reduced motor for standard, no. 40 bike chain (see parts list).   The box between my legs in the photos above house the 2, 12 volt batteries, and motor controller and throttle. 

Details of the design and dimensions are shown in the next several pictures.  Note the zinc pulleys are used both as wheel hubs (connection to axel), and to drive the back axel via a 35 inch V pulley belt.   The wheel bearings can mount to the wood frame with some movement, to enable tensioning the pulley belt.  I would buy a 34 inch, and 36 inch belt, just in case, or design in a pulley belt tensioning as in my original engine design (point C).   The middle wheel is non flanged and passive, lag bolted to the frame with a ½ inch diameter lag bolt, and used for extra weight support.  (optional).

Numbers are used on some figures to label parts.  Parts 1-9  are superimposed on pictures; these and more are listed on a parts list, including cost, supplier and web address at end of document)




Upside down side view


Dimension: a= 34 in  b= 16 in.   c=  3.5 in  d=  5 in

dimensions:  a =34 in   b= 13 in   c= 6.75  e= 6 in, but adjust block that holds lag bolted, non flanged middle wheels  directly over the track rail (optional unless needed for heavy weight riders).


Note that this motor also comes with a flat mount making it easy to attach to the front of the wood frame.  A slot at e was cut to allow clearance for the chain.   The final engine cover should completely cover the chain drive mechanism for safety.   A wood shim can be placed under the motor mount to adjust chain tension if necessary (not done in the picture below).



The motor used is a 350 watt, 25 volt, gear reduced electric bike conversion motor designed for standard bike #40 chain. 

Note that the 12 inch long, D shaped axel is ½ inch in diameter.  The free wheel gear was designed for a 15 mm axel, and  has a 15mm bore.  I used a cooper pipe fitting at the blue arrow (part 8) as a spacer to upsize ½ to 15 mm (approx..)   The picture below also shows details of drive wheel construction.  A 4 inch zinc V pulley is attached via 4 bolts (red arrow show one) through the 1/8 inch, 7 inch diameter flange disc to the 6 inch lawn mower replacement wheel.  An set screw on the pulley engages the D flat surface of the axel (not shown).   The free wheel gear has 2 set screws to engage the axel.  


A Thomas the tank engine body is connected to the top of the new motor drive frame.


Parts list, approx.. cost, suppliers and web links to suppliers


7. Sunlite easy off freewheel 24 tooth cost $8-20 dollars (note all costs are approx..)Source:

7. Sunlite trike free wheel adapter (you need both freewheel and adapter) cost $13



3. Low profile wheel bearing from McMaster Carr  cost $10 each



6. D axel ½ inch diameter, 1 foot length, from McMaster Carr, cost $10




8. NIBCO 5/8" x 1/2" FTG x C Copper Fitting Reducer 600-2 $1.50


5. Zinc 4 or 4.5 inch V pulleys from McMaster Carr, cost $12



5. V belts:  from McMaster Carr: length depends on particular geometry of your motor, axel wheel setup; 35 inches for my new engine design


Cost approx.: $8-15 dollars, depends on length. 


e. (old engine) V belt tensioner:  use a small, 1.5 inch Zinc pulley  cost $5


2 and 4.  1/8 for small wheels or 3/16 inch for large wheels;  polypropropylene sheet for flange wheels;  24 by 48 inches from United States Plastics corp: cost $14

(material to cut circular disc wheel flanges)



2. Metal 6 inch lawn mower replacement wheels (rated at 50 lbs), cost approx. $6 each



2. Plastic 6 inch “Arnold” lawn mower replacement wheels (easier to drill through, but rated at 35 lbs each) Cost $6-8


1. Roller skate replacement wheels and bearings for passive cars, approx. cost $40 for 8 wheels



Electric motor for new engine and crank car (uses  #40 bike chain), cost $65

24 Volt 350 Watt MY1016Z3 Gear Reduction Electric Motor with 9 Tooth 1/8" Bicycle Chain Sprocket



The Electric motor that I used for the old, original engine is discontinued.  Make sure you look

At the physical dimensions to make sure it will fit in the tighter constraints of the old engine design.

There are many options for 24-36 V, 350-500 watt, no. 25 chain scooter motors available from monster scooters, at website below

motor speed constrollers:  approx. cost  $30-50 but depends on the motor watts and voltage you choose.  Monster scooter sells motor kits with controllers at the link below:


9. Chain sprockets and chain sizing and link sections and tools:

Please note that the 80 toothed,  #25 mm sprocket used in the old, original engine is also discontinued.  You can find

Sprockets at :

#25 Chain at :

#40 bike chain:  from local bike store or anywhere on the net, including

Chain link tool to adjust size of bike chain:  Topeak 2011 Update Universal Chain Tool: cost  $14

chain link: KMC MISSING LINK II Bicycle Chain Link (7 and 8-Speed, 6-Pairs) cost $7 source:

chain tensioners (cost $7-10):



Hardware:  because the train car frame and trucks are made of wood,  most attachments including wheels, mounted wheel bearings, etc. are usually connected using appropriate diameter and length lag bolts with appropriate spacing and lock washers.   Wheel, flange, V pulley assemblies use appropriate length no 6 screw bolts, lock and spacing washers, and nuts. 

I connect small roller skate wheels to wooden trucks using 5/16 by 3 inch long lag bolts.  I use ½ inch by 4 inch long lag bolts for larger wheels (middle wheel of new engine), and truck pivot connection to car decks.